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                       BUREAU OF ECONOMIC GEOLOGY
                   The University of Texas at Austin
                          Austin, Texas 78712
                       John T. Lonsdale, Director


                              Guidebook 2




                             TEXAS FOSSILS:
                   _An Amateur Collector’s Handbook_


                                   By
                        William H. Matthews III

                             November 1960
                      _Second Printing, July 1963_
                     _Third Printing, August 1967_
                      _Fourth Printing, June 1971_
                    _Fifth Printing, November 1973_
                      _Sixth Printing, April 1976_
                   _Seventh Printing, November 1978_
                   _Eighth Printing, September 1981_
                     _Ninth Printing, August 1984_




                                Contents


                                                                Page
  Introduction                                                     1
  What are fossils?                                                3
  The study of fossils                                             4
      Paleobotany                                                  4
      Invertebrate paleontology                                    4
      Vertebrate paleontology                                      4
      Micropaleontology                                            4
  Preservation of fossils                                          5
      Requirements of fossilization                                5
      Missing pages in the record                                  5
  Different kinds of fossil preservation                           7
      Original soft parts of organisms                             7
      Original hard parts of organisms                             7
          Calcareous remains                                      10
          Phosphatic remains                                      10
          Siliceous remains                                       10
          Chitinous remains                                       10
      Altered hard parts of organisms                             10
          Carbonization                                           10
          Petrifaction or permineralization                       10
          Replacement or mineralization                           10
              Replacement by calcareous material                  11
              Replacement by siliceous material                   11
              Replacement by iron compounds                       11
      Traces of organisms                                         11
          Molds and casts                                         11
          Tracks, trails, and burrows                             14
          Coprolites                                              14
          Gastroliths                                             14
      Pseudofossils                                               14
          Dendrites                                               14
          Slickensides                                            16
          Concretions                                             16
  Where and how to collect fossils                                17
      Collecting equipment                                        17
      Where to look                                               19
      How to collect                                              20
  Cleaning and preparation of fossils                             21
  How fossils are named                                           21
      The science of classification                               21
      The units of classification                                 22
  Identification of fossils                                       23
  Use of identification keys                                      23
      Identification key to main types of invertebrate fossils    26
  List of Texas colleges offering geology courses                 27
  Cataloging the collection                                       31
  How fossils are used                                            31
  Geologic history                                                33
      Geologic column and time scale                              33
      The geology of Texas                                        34
          Physiography                                            35
              Trans-Pecos region                                  35
              Texas Plains                                        35
      High Plains                                                 35
      North-central Plains                                        37
      Edwards Plateau                                             37
      Grand Prairie                                               37
      Llano uplift                                                37
              Gulf Coastal Plain                                  37
      Geology                                                     37
          Precambrian rocks                                       40
          Paleozoic rocks                                         40
              Cambrian                                            40
              Ordovician                                          40
              Silurian                                            40
              Devonian                                            40
              Mississippian                                       41
              Pennsylvanian                                       41
              Permian                                             41
          Mesozoic rocks                                          42
              Triassic                                            42
              Jurassic                                            42
              Cretaceous                                          42
          Cenozoic rocks                                          43
              Tertiary                                            43
              Quaternary                                          43
  Main types of fossils                                           44
      Plant fossils                                               44
          Classification of the plant kingdom                     44
              Division Thallophyta                                44
              Division Bryophyta                                  44
              Division Tracheophyta                               44
      Animal fossils                                              48
          Phylum Protozoa                                         48
      Class Sarcodina                                             48
      Order Foraminifera                                          48
      Order Radiolaria                                            48
          Phylum Porifera                                         49
          Phylum Coelenterata                                     49
      Class Anthozoa                                              49
      Subclass Zoantharia                                         50
      Order Rugosa                                                50
      Order Scleractinia                                          50
      Order Tabulata                                              50
          Phylum Bryozoa                                          50
          Phylum Brachiopoda                                      54
      Class Inarticulata                                          54
      Class Articulata                                            56
          Phylum Mollusca                                         56
      Class Gastropoda                                            59
      Class Pelecypoda                                            59
      Class Cephalopoda                                           66
      Subclass Nautiloidea                                        66
      Subclass Ammonoidea                                         75
      Subclass Coleoidea                                          78
      Order Belemnoidea                                           78
          Phylum Annelida                                         78
          Phylum Arthropoda                                       78
              Subphylum Trilobitomorpha                           78
      Class Trilobita                                             78
              Subphylum Crustacea                                 80
      Class Ostracoda                                             80
          Phylum Echinodermata                                    80
              Subphylum Pelmatozoa                                81
      Class Cystoidea                                             81
      Class Blastoidea                                            81
      Class Crinoidea                                             81
              Subphylum Eleutherozoa                              82
      Class Asterozoa                                             82
      Subclass Asteroidea                                         82
      Subclass Ophiuroidea                                        82
      Class Echinozoa                                             82
      Subclass Echinoidea                                         82
      Subclass Holothuroidea                                      85
          Phylum Chordata                                         85
              Subphylum Hemichordata                              85
      Class Graptolithina                                         85
              Subphylum Vertebrata                                86
      Superclass Pisces                                           87
      Class Agnatha                                               87
      Class Placodermi                                            87
      Class Chondrichthyes                                        87
      Class Osteichthyes                                          87
      Superclass Tetrapoda                                        89
      Class Amphibia                                              89
      Class Reptilia                                              89
      Cotylosaurs                                                 89
      Turtles                                                     89
      Pelycosaurs                                                 89
      Therapsids                                                  89
      Ichthyosaurs                                                95
      Mosasaurs                                                   95
      Plesiosaurs                                                 95
      Phytosaurs                                                  95
      Crocodiles and alligators                                   95
      Pterosaurs                                                  95
      Dinosaurs                                                   95
      Order Saurischia                                            97
      Suborder Theropoda                                          97
      Suborder Sauropoda                                          97
      Order Ornithischia                                          97
      Suborder Ornithopoda                                        97
      Suborder Stegosauria                                        97
      Suborder Ankylosauria                                       97
      Suborder Ceratopsia                                        100
      Class Aves                                                 100
      Class Mammalia                                             100
      Subclass Allotheria                                        100
      Subclass Theria                                            100
      Order Edentata                                             100
      Order Carnivora                                            102
      Order Pantodonta                                           102
      Order Dinocerata                                           102
      Order Proboscidea                                          102
      Order Perissodactyla                                       104
      Horses                                                     104
      Titanotheres                                               104
      Chalicotheres                                              106
      Rhinoceroses                                               106
      Order Artiodactyla                                         106
      Entelodonts                                                106
      Camels                                                     106
  Books about fossils                                            108
      General works                                              108
      Nontechnical and juvenile                                  108
      Collecting helps                                           108
      Reference works                                            109
      Selected references on Texas fossils                       109
  Glossary                                                       111
  Index                                                          115




                             Illustrations


  Figures—                                                      Page
  1. Sketch of a coprolite—fossilized animal excrement            14
  2. Sketch of a gastrolith—the gizzard stone of an ancient
          reptile                                                 14
  3. Dendrites—a typical pseudofossil                             14
  4. Types of symmetry in a fossil coral                          24
  5. Bilateral symmetry in fossil brachiopod                      24
  6. A brachiopod showing specimen number and accompanying label  31
  7. Two types of micropaleontological slides                     32
  8. Typical Pennsylvanian crinoidal limestone                    41
  9. Typical Texas Foraminifera                                   49
  10. Typical radiolarians                                        49
  11. Morphology and principal parts of corals                    50
  12. Two types of bryozoans                                      50
  13. Morphology and principal parts of articulate brachiopods    54
  14. _Lingula_, a typical inarticulate brachiopod                56
  15. _Kingena wacoensis_, a common Cretaceous brachiopod         56
  16. Morphology and principal parts of gastropod shells          60
  17. Morphology and principal parts of a typical pelecypod shell 65
  18. Morphology and principal parts of the pearly nautilus       75
  19. Characteristic features of the various types of cephalopod
          sutures                                                 75
  20. Types of typical fossil annelid worms                       78
  21. Morphology and principal parts of trilobites                80
  22. Two extinct attached echinoderms, _Pentremites_ and
          _Caryocrinites_                                         81
  23. Typical modern crinoid, or “sea lily,” showing principal
          parts                                                   81
  24. Graptolites                                                 86
  25. Sketches of mastodon and mammoth teeth                     104
  26. Two views of a typical fossil horse tooth                  104


  Plates—                                                       Page
  1. Geologic time scale                                Frontispiece
  2. Types of fossil preservation                                  8
  3. Silicified brachiopods dissolved from Permian limestones of the
          Glass Mountains, Brewster County, Texas                 12
  4. Dinosaur tracks in limestone in bed of Paluxy Creek near Glen
          Rose, Somervell County, Texas                           15
  5. Fossil collecting equipment                                  18
  6-8. Fossil identification charts                            28-30
  9. Physiographic map of Texas                                   36
  10. Geologic map of Texas                                    38-39
  11. Geologic range of the major groups of plants and animals    45
  12. Fossil plants—thallophytes and tracheophytes                46
  13. Fossil plants—tracheophytes                                 47
  14. Paleozoic sponges and sponge spicules                       51
  15. Pennsylvanian corals                                        52
  16. Cretaceous and Tertiary corals                              53
  17. Pennsylvanian bryozoans and Cambrian and Mississippian
          brachiopods                                             55
  18, 19. Pennsylvanian brachiopods                           57, 58
  20. Pennsylvanian gastropods                                    61
  21. Pennsylvanian and Cretaceous gastropods                     62
  22, 23. Tertiary gastropods                                 63, 64
  24. Pennsylvanian pelecypods                                    67
  25-28. Cretaceous pelecypods                                 68-71
  29-31. Tertiary pelecypods                                   72-74
  32. Pennsylvanian and Cretaceous cephalopods                    76
  33. Cretaceous cephalopods                                      77
  34. Fossil arthropods                                           79
  35. Fossil starfishes, crinoids, and holothurian sclerites      83
  36. Cretaceous echinoids                                        84
  37. Primitive armored fish, shark teeth, and conodonts          88
  38. Comparison of the dinosaurs                                 90
  39. Comparison of Mesozoic flying and swimming reptiles         91
  40. Pelycosaur, cotylosaur, and a primitive amphibian           92
  41. Swimming reptiles                                           93
  42. Phytosaur and flying dinosaurs                              94
  43. Skull of _Phobosuchus_, from Cretaceous of Trans-Pecos Texas
                                                                  96
  44. Saurischian dinosaurs                                       98
  45. Ornithischian dinosaurs                                     99
  46, 47. Cenozoic mammals                                  101, 103
  48. Tertiary mammals                                           105
  49. Cenozoic mammals                                           107

                            [Illustration: Plate 1
                           GEOLOGIC TIME SCALE]

  ERA
      PERIOD
          EPOCH
              CHARACTERISTIC LIFE
  CENOZOIC    “Recent Life”
      QUATERNARY    1 MILLION YEARS
          Recent
          Pleistocene
      TERTIARY    64 MILLION YEARS
          Pliocene
          Miocene
          Oligocene
          Eocene
          Paleocene
  MESOZOIC    “Middle Life”
      CRETACEOUS    70 MILLION YEARS
      JURASSIC    45 MILLION YEARS
      TRIASSIC    50 MILLION YEARS
  PALEOZOIC    “Ancient Life”
      PERMIAN    55 MILLION YEARS
      CARBONIFEROUS
        PENNSYLVANIAN    30 MILLION YEARS
        MISSISSIPPIAN    35 MILLION YEARS
      DEVONIAN    55 MILLION YEARS
      SILURIAN    20 MILLION YEARS
      ORDOVICIAN    75 MILLION YEARS
      CAMBRIAN    100 MILLION YEARS
  PRECAMBRIAN ERAS
    PROTEROZOIC ERA
    ARCHEOZOIC ERA
  APPROXIMATE AGE OF THE EARTH MORE THAN 3 BILLION 300 MILLION YEARS




                             Texas Fossils
                    An Amateur Collector’s Handbook


                       William H. Matthews III[1]




                              INTRODUCTION


Almost everyone has seen the fossilized remains of prehistoric plants or
animals. These might have been the skeleton of a gigantic dinosaur, the
petrified trunk of an ancient tree, or the shells of snails or oysters
that lived in the great seas that covered Texas millions of years ago.

Each year more and more people are learning that these fossils are more
than mere curiosities. Instead, they are realizing that a good
collection of fossils provides much information about the early history
of our earth, and that fossil collecting can be a most enjoyable,
fascinating, and rewarding hobby. It is for these people that _Texas
Fossils_ was written.

This publication is primarily an amateur collector’s handbook and as
such offers many suggestions and aids to those who would pursue the
hobby of fossil collecting. It tells, for example, what fossils are,
where and how to collect them, and how they are used. Suggestions are
made as to how the specimens may be identified and catalogued, and there
are discussions and illustrations of the main types of plant and animal
fossils. Included also is a simplified geologic map of Texas and a brief
review of the geology of the State.

_Texas Fossils_ is not a comprehensive study of the paleontology of
Texas. Rather, it deals primarily with the more common species that the
average collector is likely to find. These fossils are illustrated in
the plates and figures, and these illustrations should be of some help
in identifying the specimens in one’s collection. Included for
completeness, however, are sketches and descriptions of some of the more
rare and unusual fossils, and, for general interest, there are
illustrations and descriptions of many of the extinct reptiles and
mammals that once inhabited this State.

In addition, a group of selected references has been included for the
reader who wishes to know more about earth history and paleontology.
Many of these publications provide references of a more technical nature
for the more advanced or serious collector, and some of them list
excellent collecting localities.

A minimum of technical terminology has been used, but terms not commonly
found in dictionaries, or which have not been explained in the text, are
defined in the glossary (pp. 111-114).

Many people have helped in the planning, preparation, and completion of
_Texas Fossils_, and their help is gratefully acknowledged: Dr. Keith
Young, The University of Texas; Dr. Harold Beaver, Baylor University;
and Professor Jack Boon, Arlington State College, offered helpful
suggestions and information on Cretaceous fossils; Professors Richmond
L. Bronaugh, Baylor University, and Jack T. Hughes, West Texas State
College, provided information on vertebrate collecting localities;
Professor Fred Smith, Texas A&M College, supplied data on Tertiary
collecting localities and fossils which were used in illustrations; Dr.
Saul Aronow and Professor Darrell Davis, Lamar State College of
Technology; Dr. Jules DuBar, University of Houston; and Dr. Samuel P.
Ellison, The University of Texas, made valuable suggestions which have
been incorporated into the manuscript.

Special thanks are due Drs. John T. Lonsdale, L. F. Brown, Jr., and
Peter U. Rodda, Bureau of Economic Geology, who critically read the
manuscript and contributed greatly to the presentation of the material;
Dr. John A. Wilson, The University of Texas, who read the section on
vertebrate fossils and made invaluable suggestions and criticisms; Miss
Josephine Casey, who edited the manuscript; and Mr. J. W. Macon, who
prepared the maps and charts.

Thanks are due also to Dr. G. A. Cooper, United States National Museum,
who prepared Plate 3 especially for this publication, and to R. T. Bird
and the American Museum of Natural History for photographs used in
Plates 4 and 43. Plates 38 and 39 were provided through the courtesy of
Dr. J. W. Dixon, Jr., and the Geology Department of Baylor University.
The other photographs were prepared by the writer. To Sarah Louise
Wilson, Lamar State College of Technology, the writer gratefully
acknowledges her tireless and painstaking efforts in preparing the many
fine drawings which make up the balance of the illustrations.




                           WHAT ARE FOSSILS?


_Fossils are the remains or evidence of ancient plants or animals that
have been preserved in the rocks of the earth’s crust._ Most fossils
represent the preservable hard parts of some prehistoric organism that
once lived in the area in which the remains were collected.

The word fossil is derived from the Latin word _fossilis_, meaning “dug
up,” and for many years any unusual object dug out of the ground was
considered to be a “fossil.” For this reason some of the earlier books
dealing with fossils include discussions of rocks, minerals, and other
inorganic objects.

There is much evidence to indicate that man has been interested in
fossils since the very earliest times, and fossil shells, bones, and
teeth have been found associated with the remains of primitive and
prehistoric men. It is quite possible that the owners of these objects
believed that they possessed supernatural powers, such as healing
properties or the ability to remove curses.

During the earliest periods of recorded history, certain Greek scholars
found the remains of fish and sea shells in desert and mountainous
regions. These men were greatly puzzled by the occurrence of these
objects at such great distances from the sea, and some of them devoted
considerable time to an explanation of their presence.

In 450 B.C., Herodotus noticed fossils in the Egyptian desert and
correctly concluded that the Mediterranean Sea had once been in that
area.

Aristotle in 400 B.C. stated that fossils were organic in origin but
that they were embedded in the rocks as a result of mysterious plastic
forces at work within the earth. One of his students, Theophrastus
(about 350 B.C.), also believed that fossils represented some form of
life but thought that they had developed from seeds or eggs that had
been planted in the rocks.

Strabo (about 63 B.C. to A.D. 20) was another important Greek scholar
who attempted to explain the presence of fossils. He noted the
occurrence of marine fossils well above sea level and correctly inferred
that the rocks containing them had been subjected to considerable
elevation.

During the “Dark Ages” fossils were alternately explained as freaks of
nature, the remains of attempts at special creation, and devices of the
devil which had been placed in the rocks to lead men astray. These
superstitious beliefs and the opposition from religious authorities
hindered the study of fossils for hundreds of years.

In approximately the middle of the fifteenth century the true origin of
fossils was generally accepted, and they were considered to be the
remains of prehistoric organisms which had been preserved in the earth’s
crust. With the definite recognition of fossils as organic remains, many
of the more primitive theories were discarded for one just as
impractical—these remains were considered remnants of the Great Flood as
recorded in the Scriptures. The resulting controversy between scientists
and theologians lasted for about 300 years.

During the Renaissance several of the early natural scientists concerned
themselves with investigations of fossils. Noteworthy among these was
Leonardo da Vinci, the famous Italian artist, naturalist, and engineer.
Leonardo insisted that the Flood could not be responsible for all
fossils nor for their occurrence in the highest mountains. He reaffirmed
the belief that fossils were indisputable evidence of ancient life, and
that the sea had once covered northern Italy. Leonardo explained that
the remains of the animals that had inhabited this ancient body of water
were buried in the sediments of the sea floor, and that at some later
date in earth history this ocean bottom was elevated well above sea
level to form the Italian peninsula.

In the late eighteenth and early nineteenth centuries the study of
fossils became firmly established as a science, and since that time
fossils have become increasingly important to the geologist.




                          THE STUDY OF FOSSILS


The study of fossils is called _paleontology_ (Greek _palaios_, ancient;
_ontos_, a being; _logos_, word or discourse). Information gathered with
the help of paleontology has greatly increased the knowledge of ancient
plants and animals and of the world in which they lived.

Fossils represent the remains of such great numbers and various types of
organisms that paleontologists have found it helpful to establish four
main divisions within their science.


                              Paleobotany

Paleobotany deals with the study of fossil plants and the record of the
changes which they have undergone.


                       Invertebrate Paleontology

This is the study of fossil animals without a backbone or spinal column.
These include such forms as fossil protozoans (tiny one-celled animals),
snails, clams, starfish, and worms, and usually represent the remains of
animals that lived in prehistoric seas.

Because invertebrate remains are the most common fossils in Texas, this
book is devoted largely to the discussion of invertebrate fossils and
their method of collection.


                        Vertebrate Paleontology

The vertebrate paleontologist studies the fossils of animals which
possessed a backbone or spinal column. The remains of fish, amphibians,
reptiles, birds, and mammals are typical vertebrate fossils.


                           Micropaleontology

Micropaleontology is the study of fossils that are so small that they
are best studied under a microscope. These tiny remains are called
microfossils and usually represent the shells or fragments of minute
plants or animals. Because of their small size, microfossils can be
brought out of wells without being damaged by the mechanics of drilling
or coring. For this reason microfossils are particularly valuable to the
petroleum geologist who uses them to identify rock formations thousands
of feet below the surface.




                        PRESERVATION OF FOSSILS


The majority of fossils are found in marine _sedimentary rocks._ These
are rocks that were formed when salt-water sediments, such as limy muds,
sands, or shell beds, were compressed and cemented together to form
rocks. Only rarely do fossils occur in igneous and metamorphic rocks.
The _igneous rocks_ were once hot and molten and had no life in them,
and _metamorphic rocks_ have been so greatly changed or distorted that
any fossils that were present in the original rock have usually been
destroyed or so altered as to be of little use to the paleontologist.

But even in the sedimentary rocks only a minute fraction of prehistoric
plants and animals have left any record of their existence. This is not
difficult to understand in view of the rather rigorous requirements of
fossilization.




                     REQUIREMENTS OF FOSSILIZATION


Although a large number of factors ultimately determine whether an
organism will be fossilized, the three basic requirements are:

1. _The organism should possess hard parts._ These might be shell, bone,
teeth, or the woody tissue of plants. However, under very favorable
conditions of preservation it is possible for even such fragile material
as an insect or a jellyfish to become fossilized.

2. _The organic remains must escape immediate destruction after death._
If the body parts of an organism are crushed, decayed, or badly
weathered, this may result in the alteration or complete destruction of
the fossil record of that particular organism.

3. _Rapid burial in a material capable of retarding decomposition._ The
type of material burying the remains usually depends upon where the
organism lived. The remains of marine animals are common as fossils
because they fall to the sea floor after death, and here they are
covered by soft muds which will be the shales and limestones of later
geologic periods. The finer sediments are less likely to damage the
remains, and certain fine-grained Jurassic limestones in Germany have
faithfully preserved such delicate specimens as birds, insects, and
jellyfishes.

Ash falling from nearby volcanoes has been known to cover entire
forests, and some of these fossil forests have been found with the trees
still standing and in an excellent state of preservation.

Quicksand and tar are also commonly responsible for the rapid burial of
animals. The tar acts as a trap to capture the beasts and as an
antiseptic to retard the decomposition of their hard parts. The Rancho
La Brea tar pit at Los Angeles, California, is famous for the large
number of fossil bones that have been recovered from it. These include
such forms as the sabre-tooth cat, giant ground sloths, and other
creatures that are now extinct. The remains of certain animals that
lived during the Ice Ages have been incorporated into the ice or frozen
ground, and some of these frozen remains are famous for their remarkable
degree of preservation.




                      MISSING PAGES IN THE RECORD


Although untold numbers of organisms have lived on the earth in past
ages, only a minute fraction of these have left any record of their
existence. Even if the basic requirements of fossilization have been
fulfilled, there are still other reasons why some fossils may never be
found.

For example, large numbers of fossils have been destroyed by erosion or
their hard parts have been dissolved by underground waters. Others were
entombed in rocks that were later subjected to great physical change,
and fossils enclosed in these rocks are usually so damaged as to be
unrecognizable.

Then, too, many fossiliferous rocks cannot be studied because they are
covered by water or great thicknesses of sediments, and still others are
situated in places that are geographically inaccessible. These and many
other problems confront the paleontologist as he attempts to catalog the
plants and animals of the past.

The missing pages in the fossil record become more obvious and more
numerous in the older rocks of the earth’s crust. This is because the
more ancient rocks have had more time to be subjected to physical and
chemical change or to be removed by erosion.




                 DIFFERENT KINDS OF FOSSIL PRESERVATION


There are many different ways in which plants and animals may become
fossilized. The method of preservation is usually dependent upon (1) the
original composition of the organism, (2) where it lived, and (3) the
forces that affected it after death.

Most paleontologists recognize four major types of preservation, each
being based upon the composition of the remains or the changes which
they have undergone.




                    ORIGINAL SOFT PARTS OF ORGANISMS


This type of fossil is formed only under very special conditions of
preservation. To be preserved in this manner, the organism must be
buried in a medium capable of retarding decomposition of the soft parts.
Materials that have been known to produce this type of fossilization are
frozen soil or ice, oil-saturated soils, and amber (fossil resin). It is
also possible for organic remains to become so desiccated that a natural
mummy is formed. This usually occurs only in arid or desert regions and
when the remains have been protected from predators and scavengers.

Probably the best-known examples of preserved soft parts of fossil
animals have been discovered in Alaska and Siberia. The frozen tundra of
these areas has yielded the remains of large numbers of frozen
mammoths—a type of extinct elephant (Pl. 49). Many of these huge beasts
have been buried for as long as 25,000 years, and their bodies are
exposed as the frozen earth begins to thaw. Some of these giant
carcasses have been so well preserved that their flesh has been eaten by
dogs and their tusks sold by ivory traders. Many museums display the
original hair and skin of these elephants, and some have parts of the
flesh and muscle preserved in alcohol.

Original soft parts have also been recovered from oil-saturated soils in
eastern Poland. These deposits yielded the well-preserved nose-horn, a
foreleg, and part of the skin of an extinct rhinoceros.

The natural mummies of ground sloths have been found in caves and
volcanic craters in New Mexico and Arizona. The extremely dry desert
atmosphere permitted thorough dehydration of the soft parts before decay
set in, and specimens with portions of the original skin, hair, tendons,
and claws have been discovered.

One of the more interesting and unusual types of fossilization is
preservation in amber. This type of preservation was made possible when
ancient insects were trapped in the sticky gum that exuded from certain
coniferous trees. With the passing of time this resin hardened, leaving
the insect encased in a tomb of amber, and some insects and spiders have
been so well preserved that even fine hairs and muscle tissues may be
studied under the microscope.

Although the preservation of original soft parts has produced some
interesting and spectacular fossils, this type of fossilization is
relatively rare, and the paleontologist must usually work with remains
that have been preserved in stone.




                    ORIGINAL HARD PARTS OF ORGANISMS


Almost all plants and animals possess some type of hard parts which are
capable of becoming fossilized. Such hard parts may consist of the shell
material of clams, oysters, or snails, the teeth or bones of
vertebrates, the exoskeletons of crabs, or the woody tissue of plants.
These hard parts are composed of various minerals which are capable of
resisting weathering and chemical action, and fossils of this sort are
relatively common.

Many of the fossil mollusks found in the Tertiary and Cretaceous rocks
of Texas have been preserved in this manner. In some of the specimens
the original shell material is so well preserved that the iridescent
mother-of-pearl layer of the shell is found virtually intact. This type
of preservation is less common, however, in the older rocks of the
State.

                         [Illustration: PLATE 2
                     Types of Fossil Preservation]

  Figures—
    1. Internal mold of a Texas Cretaceous ammonite (×½).
    2. Internal and external molds of gastropods and pelecypods in Cedar
          Park limestone member of the Walnut clay of Comanchean age
          (×½). Specimen from quarry near Cedar Park, Williamson County,
          Texas.
    3. Internal mold of a Texas Cretaceous pelecypod (×½).
    4. Fossil worm tubes on mold of a Cretaceous ammonite (×½).
    5. Petrified or permineralized mammal bone of Tertiary age (×½).
    6. Internal mold (steinkern) of a typical Texas Cretaceous gastropod
          (×½).
    7. Carbon residue of a Tertiary fish (×¼).

At certain localities in north and central Texas the Woodbine sands of
Upper Cretaceous age (geologic time scale and geologic map, Pls. 1, 10)
contain large numbers of shark and fish teeth (Pl. 37), fish scales and
vertebrae. The remains of these vertebrates are unusually well preserved
and are prized by both amateur and professional collectors.


                           Calcareous Remains

Hard parts composed of calcite (calcium carbonate) are very common among
the invertebrates. This is particularly true of the shells of clams,
snails, and corals. Many of these shells have been preserved with little
or no evidence of physical change (Pl. 2).


                           Phosphatic Remains

The bones and teeth of vertebrates and the exoskeletons of many
invertebrates contain large amounts of calcium phosphate. Because this
compound is particularly weather resistant, many phosphatic remains
(such as the fish teeth in the Woodbine sands) are found in an excellent
state of preservation.


                           Siliceous Remains

Many organisms having skeletal elements composed of silica (silicon
dioxide) have been preserved with little observable change. The
siliceous hard parts of many microfossils and certain types of sponges
have become fossilized in this manner (Pl. 14).


                           Chitinous Remains

Some organisms have an exoskeleton (outer body covering) composed of
chitin, a material that is similar to finger nails. The fossilized
chitinous exoskeletons of arthropods and other organisms are commonly
preserved as thin films of carbon because of their chemical composition
and method of burial.




                    ALTERED HARD PARTS OF ORGANISMS


The original hard parts of an organism normally undergo great change
after burial. These changes take place in many ways, but the type of
alteration is usually determined by the composition of the hard parts
and where the organism lived. Some of the more common processes of
alteration are discussed below.


                             Carbonization

This process, known also as distillation takes place as organic matter
slowly decays after burial. During the process of decomposition, the
organic matter gradually loses its gases and liquids leaving only a thin
film of carbonaceous material (Pl. 2, fig. 7). This is the same process
by which coal is formed, and large numbers of carbonized plant fossils
have been found in many coal deposits.

In Texas the carbonized remains of plants, fish, and certain
invertebrates have been preserved in this manner, and some of these
carbon residues have accurately recorded even the most minute structures
of these organisms.


                   Petrifaction or Permineralization

Many fossils have been permineralized or petrified—literally turned to
stone. This type of preservation occurs when mineral-bearing ground
waters infiltrate porous bone, shell, or plant material. These
underground waters deposit their mineral content in the empty spaces of
the hard parts making them heavier and more resistant to weathering.
Some of the more common minerals deposited in this manner are calcite,
silica, and various compounds of iron.


                     Replacement or Mineralization

This type of preservation takes place when the original hard parts of
organisms are removed after being dissolved by underground water. This
is accompanied by almost simultaneous deposition of other substances in
the resulting voids. Some replaced fossils will have the original
structure destroyed by the replacing minerals. Others, as in the case of
certain silicified tree trunks, may be preserved in minute detail.

Although more than 50 minerals have been known to replace original
organic structures, the most frequent replacing substances are calcite,
dolomite (a calcium magnesium carbonate), silica, and certain iron
compounds.

                   Replacement by calcareous material

Calcareous replacement occurs when the hard parts of an organism are
replaced by calcite, dolomite, or aragonite (a mineral which is composed
of calcium carbonate but which is less stable than calcite). The
exoskeletons of many corals, echinoderms, brachiopods, and mollusks have
been replaced in this manner.

                   Replacement by siliceous material

When the original organic hard parts have been replaced by silica the
fossil is said to have undergone silicification, and this type of
replacement often produces a very high degree of preservation. This is
particularly true of the silicified Permian (geologic time scale, Pl. 1)
fossils from the Glass Mountains in Brewster County. These fossils are
embedded in limestone which must be dissolved in vats of acid, and after
the enclosing rock has been dissolved the residue yields an amazing
variety of perfectly preserved invertebrate fossils (Pl. 3).

Silicified Cretaceous fossils have been recovered from the Edwards
limestone of central Texas. The silicified fauna is restricted to a few
scattered localities, each of which may yield many unusually
well-preserved fossils.

                     Replacement by iron compounds

Several different iron compounds have been known to replace organic
matter. Many Texas limestones contain fossil snails and clams which have
had their original shell material replaced by iron compounds such as
limonite, hematite, marcasite, or pyrite. Certain of the fossiliferous
Tertiary sandstones of the Texas Gulf Coast area contain large amounts
of glauconite which commonly replaced organic material.

In some areas entire faunas have been replaced by iron compounds. Such
is the case in the famous “Pyrite Fossil Zone” of the Pawpaw formation
(Lower Cretaceous) in Tarrant County. The fossils in this part of the
formation are very small or “dwarfed” and have been replaced by
limonite, hematite, or pyrite. Ammonites, clams, snails, and corals are
particularly abundant at this locality.




                          TRACES OF ORGANISMS


Fossils consist not only of plant and animal remains but of any evidence
of their existence. In this type of fossilization there is no direct
evidence of the original organism, rather there is some definite
indication of the former presence of some ancient plant or animal.
Objects of this sort normally furnish considerable information as to the
identity or characteristics of the organism responsible for them.


                            Molds and Casts

Many shells, bones, leaves, and other forms of organic matter are
preserved as molds and casts. If a shell had been pressed down into the
ocean bottom before the sediment had hardened into rock, it may have
left the impression of the exterior of the shell. This impression is
known as a _mold_ (Pl. 2). If at some later time this mold was filled
with another material, this produced a _cast_. This cast will show the
original external characteristics of the shell. Such objects are called
_external molds_ if they show the external features of the hard parts
(Pl. 2, fig. 2) and _internal molds_ (Pl. 2, fig. 3) if the nature of
the inner parts is shown.

Molds and casts are to be found in almost all of the fossil-bearing
rocks of Texas, and they make up a large part of most fossil
collections. It is particularly common to find fossil clams and snails
preserved by this method. This is primarily because their shells are
composed of minerals that are relatively easy to dissolve, and the
original shell material is often destroyed.

                         [Illustration: PLATE 3
                         Silicified Brachiopods

All specimens from Permian limestones of the Glass Mountains, Brewster
County, Texas]

  Figures—
    1, 2. _Avonia_ sp., ×2. Ventral and side view of two pedicle valves
          showing long slender spines.
    3. _Avonia_ sp., ×6. Young specimen showing attachment ring at apex.
    4-6. _Muirwoodia multistriatus_ Meek, ×4. Respectively, side and
          ventral view of pedicle valve and dorsal view of brachial
          valve.
    7-9. _“Marginifera” opima_ Girty. Respectively, ventral and side
          view of pedicle valve showing long stout spines (×4) and
          interior of brachial valve showing muscle scars and brachial
          ridges (×2).
    10-13. _Aulosteges tuberculatus_ R. E. King, ×4. Respectively, side
          and interior view of brachial valve showing muscle scars;
          ventral view of pedicle valve showing brush of attachment
          spines on ears; and ventral view of a young pedicle valve.
    14. _Avonia_ sp., ×4. Ventral view of a specimen with long spines.
    15, 16. _Avonia subhorrida_ (Meek), ×2. Ventral view of a pedicle
          valve and dorsal view of a brachial valve showing spines on
          both.
    17. _Avonia signata_ (Girty), ×2. Dorsal view of a large specimen
          showing hairlike spines on brachial valve.
    18-20. _Prorichthofenia permiana_ (Shumard). Respectively, side and
          posterior view of pedicle valve (×4) and interior of dorsal
          valve (×2) showing anchor spines and interior spines of the
          brachial valve.
    21. _Heteralosia hystricula_ (Girty), ×2. Cluster of individuals
          attached to a large _Marginifera_.
      Photograph courtesy of Dr. G. A. Cooper, U. S. National Museum.


                      Tracks, Trails, and Burrows

Many animals have left records of their movements over dry land or the
sea bottom. Some of these, such as footprints (Pl. 4), indicate not only
the type of animal that left them but often provide valuable information
about the animal’s environment.

Thus, the study of a series of dinosaur tracks would not only indicate
the size and shape of the foot but also provide some information as to
the weight and length of the animal. In addition, the type of rock
containing the track would help determine the conditions under which the
dinosaur lived.

Some of the world’s most famous dinosaur tracks are to be found in the
Lower Cretaceous limestones in Somervell County, Texas. These
footprints, which are about 110,000,000 years old (Pl. 4), were
discovered in the bed of Paluxy Creek near the town of Glen Rose. Large
segments of the rock containing these tracks were collected by
paleontologists of the American Museum of Natural History in New York
City and the Texas Memorial Museum at Austin. Great slabs of limestone
were transported to the museums, replaced in their original position,
and are now on display as mute evidence of the gigantic size of these
tremendous reptiles.

Invertebrates also leave tracks and trails of their activities, and
these markings may be seen on the surfaces of many sandstone and
limestone deposits. These may be simple tracks, left as the animal moved
over the surface, or the burrows of crabs or other burrowing animals.
Markings of this sort provide some evidence of the manner of locomotion
of these organisms and of the type of environment that they inhabited.


                               Coprolites

Coprolites are fossil dung or body waste (fig. 1). These objects can
provide valuable information as to the food habits or anatomical
structure of the animal that made them.

     [Illustration: Fig. 1. Sketch of a coprolite—fossilized animal
                              excrement.]


                              Gastroliths

These highly polished well-rounded stones (fig. 2) are believed to have
been used in the stomachs of reptiles for grinding the food into smaller
pieces. Large numbers of these “stomach stones” have been found with the
remains of certain types of dinosaurs.

 [Illustration: Fig. 2. Sketch of a gastrolith—the gizzard stone of an
                           ancient reptile.]




                             PSEUDOFOSSILS


Among the many inorganic objects formed by nature there are some that
bear superficial resemblance to plants or animals. Because they are
often mistaken for organic remains, these objects have been called
_pseudofossils_, or “false fossils.”


                               Dendrites

[Illustration: Fig. 3. Dendrites. These thin branching mineral deposits
       bear a marked resemblance to plants, hence they are called
                            pseudofossils.]

Although these closely resemble the remains of ferns or other plant
material (fig. 3), dendrites are actually thin incrustations of
manganese dioxide. They are often found along the bedding planes of
Cretaceous and Paleozoic (geologic time scale, Pl. 1) limestones in many
parts of Texas.

                         [Illustration: Plate 4
  Dinosaur tracks in limestone in bed of Paluxy Creek near Glen Rose,
                        Somervell County, Texas.
     Photograph courtesy of the American Museum of Natural History.
                Permission to reproduce by R. T. Bird.]


                              Slickensides

These are striations that are produced when rock surfaces move past each
other while being fractured. Slickensides may superficially resemble
certain of the Pennsylvanian coal plants of Texas.

Since slickensides are commonly at an angle to the bedding plane and
plant remains lie parallel to the bedding plane, the two are usually
easily distinguished.


                              Concretions

Many shales and sandstones contain hardened masses of minerals and rock
that are often mistaken for fossils. These masses, called concretions,
are usually found weathered out of the surrounding rock and may assume
the shape of bones, flowers, vegetables, turtles, etc. Although these
concretions do not represent organic remains, it is sometimes possible
to find true fossils inside them.




                    WHERE AND HOW TO COLLECT FOSSILS


In fossil collecting, as in most “collecting” hobbies, the key to
success lies in knowing where to look, what equipment to use, and the
most effective methods of collecting.




                          COLLECTING EQUIPMENT


Fossil collecting is a relatively inexpensive hobby because it requires
a minimum of supplies and equipment. However, as in almost any hobby,
there are certain basic items of equipment that must be acquired.


                                 Hammer

The hammer is the basic tool in the collector’s kit. Almost any type of
hammer is satisfactory, but as collecting experience is gained it may be
desirable to get a geologist’s hammer. These hammers, also called
mineralogist’s or prospector’s picks, are of two types. One type has a
square head on one end and a pick on the other (Pl. 5): the other type
is similar to a stonemason’s or bricklayer’s hammer and has a chisel end
instead of the pointed pick end. The square head of the hammer is useful
in breaking or chipping harder rocks, and the chisel or pick end is good
for digging, prying, and splitting soft rocks.


                             Collecting Bag

It will be necessary to have some type of bag in which to carry
equipment, fossils, and other supplies. A Boy Scout knapsack, musette
bag (Pl. 5), hunting bag, or similar canvas or leather bag is suitable.


                                Chisels

A pair of chisels is useful when fossils must be chipped out of the
surrounding rock. Two sizes, preferably ½ and 1 inch, will usually
suffice. A small sharp punch or awl is effective in removing smaller
specimens from the softer rocks.


                           Wrapping Materials

Some specimens are more fragile than others, and these should be handled
with special care. Several sheets of newspaper should always be kept in
the collecting bag, and each specimen should be wrapped individually as
it is collected. Such precautions taken in the field will usually
prevent prized specimens from being broken or otherwise damaged. In
addition to newspaper, it is wise to carry a supply of tissue paper in
which to wrap more fragile specimens.


                       Map, Notebook, and Pencil

It is most important to have some method of recording where the fossils
were found. It is very easy to forget where the material was collected,
and one should _never_ rely on memory. A small pocket-sized notebook is
inexpensive and just the right size to carry in the field.

A highway or county map should be used to find the geographic location
of each collecting locality. Maps of Texas counties can be obtained from
the Texas Highway Department, File D-10, Austin 14, Texas. These maps
come in three different sizes, but for most purposes the 18×25-inch
sheets, with a scale of ½ inch = 1 mile, will be satisfactory. These are
available for all counties and may be purchased at a nominal price.


                            Magnifying Glass

A magnifying glass or hand lens (Pl. 5) is useful for looking at small
specimens and will also prove helpful in examining the finer details of
larger fossils. A 10-power magnification is satisfactory for most
purposes, and several inexpensive models are available.


                          Paper or Cloth Bags

Small bags are useful in separating specimens from different localities.
Heavy-duty hardware bags for large rough material and medium-weight
grocery bags for smaller specimens may be used. Locality data may be
written directly on the bag or on a label placed inside with the
fossils. As an added precaution some collectors do both. The more
serious collector may want to use a cloth geological sample bag (Pl. 5).

                         [Illustration: Plate 5
                      FOSSIL COLLECTING EQUIPMENT]

  GEOLOGIC HAMMER (Chisel end)
  MAGNIFYING GLASS
  GEOLOGIC HAMMER (Pick end)
  COLLECTING BAG
  SAMPLE SACK


                           Other Useful Items

The items described above are those that are most needed and constitute
the basic equipment of the fossil hunter. The serious amateur may wish
to include certain additional items which will place his collecting on a
more professional basis. Some of these accessory items are:

1. A _topographic map_ of the collecting area. These are available for
many parts of the State and are published and distributed at nominal
cost by the United States Geological Survey, Washington, D. C., and/or
Denver, Colorado. The Survey can supply an index sheet showing all such
maps available for Texas.

2. A _geologic map_ of the collecting area if one is available. The list
of publications of the Bureau of Economic Geology should be consulted to
see if a geologic report or map of the area has been published. This
list may be obtained without charge from the Bureau of Economic Geology,
The University of Texas, Austin 12, Texas.

3. The _geologic map of Texas_. Although a geologic map of Texas is
included in this publication (Pl. 10), the scale is so small that its
use is somewhat limited. For more detailed work a larger geologic map in
color (scale: 1 inch = 31.56 miles) may be ordered from the Bureau. The
sale price is 25 cents.

4. A _compass_ for more accurate location of collecting localities.

5. _Adhesive_ or _masking tape_. The locality information can be written
on the tape and applied directly to the specimen.

6. _Paper labels_ (about 3×5 inches). A properly completed label should
be placed inside each bag of material.




                             WHERE TO LOOK


Knowing where to look for fossils is a very important part of fossil
collecting. It has already been pointed out that igneous and metamorphic
rocks are not likely to be fossiliferous, but that most fossils are
found in marine sedimentary rocks. These sediments were deposited under
conditions that were favorable for organisms during life and which
facilitated preservation after death. Limestones, limy shales, and
certain types of sandstones are typically deposited under such
conditions.

One should look particularly for areas where rocks formed from marine
sediments lie relatively flat and have not been greatly disturbed by
heat, pressure, and other physical or chemical changes. If the rocks
appear to have undergone considerable folding and fracturing, there is
great likelihood that any fossils that were present have been destroyed
or damaged by this action.

Quarries are good places to look but one should be sure to obtain
permission before entering. Rock exposures in quarries are rather fresh
but have undergone some weathering. Quarries have been opened in many of
the limestone formations of Texas, and large numbers of fine specimens
have been collected in some of these excavations. Certain Lower
Cretaceous limestones are useful for road metal, building stone, or in
the manufacture of portland cement, and extensive quarrying has been
undertaken in the Edwards Plateau region of Texas (Pl. 9). Bones and
petrified wood are frequently found in sand and gravel quarries in many
parts of the State.

Particular attention should be given to all railroad and highway cuts as
rocks exposed in this way are usually still in their original position
and are fairly well weathered. Cuts made by recent construction are
usually more productive after they have undergone a period of weathering
as this helps to separate the fossils from their enclosing rocks.

Gullies, canyons, and stream beds are also good places to examine. These
areas are continually subjected to the processes of erosion or stream
action, and new material is uncovered year after year.

If there are abandoned coal mines nearby, the dumps of waste rock around
the mine shafts could be checked. A careful examination of such waste
may reveal fine specimens of well-preserved plant fossils.

Coal has been mined in several parts of Texas, and abandoned shafts or
dumps are still present in some counties. The bituminous coals of Texas
are predominantly Pennsylvanian in age, and mining has been carried on
in the following counties: Eastland, Erath, Jack, Palo Pinto, Parker,
Wise, Young.




                             HOW TO COLLECT


When a likely collecting spot has been located, the ground should be
examined very carefully to see if there are any rock fragments which
contain pieces of shell or the imprints of leaves or other organisms.

If the fossils have been freed by weathering, they can be easily picked
up and placed in the bag. Many times, however, it will be necessary to
take the hammer and very carefully remove the surrounding rock. Smaller
specimens may be more safely freed with the careful use of the proper
size chisel by gently tapping the chisel and gradually chipping away the
_matrix_—the rock that is holding the specimen. After most of the matrix
has been removed, the fossil should be carefully wrapped and placed in
the collecting bag.

Before leaving a collecting locality, one should be sure to record its
geographic location and the geologic age of the rock in which the
fossils were found. The place should be located on the map and the
locality entered in the notebook in such a manner that it could easily
be located again for additional collecting. If a county or topographic
map is available, it is wise to mark the locality on the map. The
geographic and geologic data should be written on a label placed in the
bag of fossils collected at that particular locality. In addition, many
collectors find it helpful to write the locality on the outside of each
bag of fossils.

Material from separate localities should be kept in individual cloth or
paper bags, and the collector should take every precaution to keep the
labels with their respective fossils. Remember that _a fossil without a
locality is hardly worth the paper it is wrapped in_.

The collector should _always_ ask the land owner’s permission before
entering or collecting on private property. One should respect all
property, especially livestock and fences, and leave the area cleaner
than when entered. If these precautions are observed, future collectors
will probably be welcome to return for additional collecting.




                  CLEANING AND PREPARATION OF FOSSILS


It is usually necessary to do the final cleaning and preparation of
fossils at home or in the laboratory, for most fossils brought in from
the field require considerable preparation before they are ready for
display.

Excess matrix should be carefully removed with hammer and chisel; blows
should always be directed away from the fossil. Smaller tools (needles,
tweezers, and awls) should be used in the final preparation stage, and
one should work carefully to avoid damaging the specimen. Before
starting the final cleaning, it will be helpful to place the fossils in
water and let them soak overnight. This will loosen much of the excess
rock, and most of the softer material can then be removed with a small
scrub brush or tooth brush. Mounted needles can be used to clean more
delicate specimens or around the smaller structures of larger fossils.
It may be advisable to use the magnifying glass when working with small
fossils or with delicate surface structures of larger specimens.

Broken fossils can be repaired with clear plastic household cement, and
specimens that are crumbling may be coated with pure white shellac,
thinned collodion, or clear nail polish. The latter is preferred as it
is not as likely to crack. Fragments of bone are particularly apt to
crumble upon exposure to the air. This type of fossil is normally quite
fragile and should be excavated with great care and shellaced as soon as
dry.

Dilute hydrochloric acid may be used in removing silicified fossils from
a calcareous matrix. The material to be etched should be placed in a
pottery or glass container and covered with water. Acid should then be
added to the water very slowly and until large numbers of bubbles are
given off. Each time the bubbling ceases, more acid should be added and
this process should be repeated until the fossil is free of matrix. This
procedure should be carried on in a well-ventilated place, and the acid
should be handled with extreme caution. Hydrochloric acid can cause
damage or serious injury and the fumes are extremely corrosive.




                         HOW FOSSILS ARE NAMED


In order to get the maximum pleasure out of fossil collecting, most
amateur paleontologists want to identify and classify the fossils that
they have collected. This requires some knowledge of how fossils are
classified and how they receive their scientific names.




                     THE SCIENCE OF CLASSIFICATION


The number of organisms, both living and extinct, is so great that some
system of classification is needed to link them all together. Many
fossils bear distinct similarities to plants and animals that are living
today, and for this reason paleontological classification is similar to
that used to classify modern organisms. This system, known as the system
of _binomial nomenclature_, was first used consistently in 1758 by Linné
(or Linnaeus), an early Swedish naturalist.

Scientific names established in accordance with the principles of
binomial nomenclature consist of two parts: the _generic_ (or _genus_)
name and the _trivial_ name. These names are commonly derived from Greek
or Latin words which are usually descriptive of the organism or fossil
being named. They may, however, be derived from the names of people or
places, and in such instances the names are always Latinized. Greek or
Latin is used because they are “dead” languages and not subject to
change. They are also “international” languages in that scientists all
over the world can use the same names regardless of what language they
write in. The system of binomial nomenclature has led to the development
of the science of _taxonomy_, the systematic classification and naming
of plants and animals according to their relationships.




                      THE UNITS OF CLASSIFICATION


The world of organic life has been divided into the plant and animal
kingdoms. These kingdoms have been further divided into larger divisions
called _phyla_ (from the Greek word _phylon_, a race). Each phylum is
composed of organisms with certain characteristics in common. For
example, all animals with a spinal cord (or notochord) are assigned to
the phylum Chordata.

The phylum is reduced to smaller divisions called _classes_, classes are
divided into _orders_, orders into _families_, families into _genera_,
and each genus is divided into still smaller units called _species_. A
species may be further reduced to subspecies, varieties, or other
subspecific categories, but these need not concern us in a publication
of this nature.

The following table illustrates the use of binomial nomenclature in the
classification of man, a clam, and a dog.

  Unit        Man         Dog           Clam
  Kingdom     Animalia    Animalia      Animalia
  Phylum      Chordata    Chordata      Mollusca
  Class       Mammalia    Mammalia      Pelecypoda
  Order       Primates    Carnivora     Eulamellibranchia
  Family      Hominidae   Canidae       Veneridae
  Genus       _Homo_      _Canis_       _Venus_
  Species     _sapiens_   _familiaris_  _mercenaria_

The generic name and the trivial name constitute the _scientific name_
of a species and according to this system of classification the
scientific name of all living men is _Homo sapiens_. It is obvious that
there are many variations among individual men, but all men have certain
general characteristics in common and are therefore placed in the same
species.

In a scientific name, the generic name is always started with a capital
letter and the trivial name with a small letter. Both names must be
italicized or underlined.

The name of the author (the person who first described the fossil)
usually appears following the scientific name. The date of the
scientific publication containing the original description of the fossil
is often placed after the author. For example:

             _Turrilites worthensis_ Adkins and Winton 1920

With the large numbers of plants and animals that are living today, plus
those of the past, random naming would result in much confusion. For
this reason scientists have established strict rules that must be
followed when a specimen is named. The strict application of these rules
enables scientists in all parts of the world to assign scientific names
without fear of duplication.




                       IDENTIFICATION OF FOSSILS


The beginning collector is usually content to know if his specimen is a
clam or a snail or a fern or a palm leaf. But as the collection grows,
it becomes increasingly desirable to know the scientific name of each
fossil.

When he starts to identify fossils it may be helpful to show them to a
geology teacher if a college or university is nearby. Most teachers are
glad to be of help and will probably have similar specimens in their own
collections. As all colleges do not have geology departments, a list of
institutions with geologists on their faculties is included at the end
of this section of the handbook (p. 27). In addition, many of the
science teachers in the public schools are familiar with fossils and can
give helpful suggestions as to how to classify material.

Museums are also good places from which to get help. If the museum has a
geological collection, it will be most helpful to compare specimens with
the fossils in their collections and to ask the museum personnel for
advice. In addition to the above sources of information, local
professional geologists are usually familiar with the geology of the
local area and the paleontological literature of the region.

Possibly local librarians can recommend books, encyclopedias, or other
publications that will be of help. Members of a local rock and mineral
club, if one is available, are another source of information. Many times
these collectors can pass along good ideas and tell exactly which books
to consult.

After books or journals describing the fossils of the area have been
located, the collected specimens should be closely compared with any
illustrations that are shown. Each fossil should be examined carefully,
its more characteristic features noted, and it should again be compared
with the illustrations and descriptions in the book. The phylum or class
to which the specimen belongs should be determined first. For example,
the genus and species of a certain fossil may not be known, but it looks
like a snail and accordingly it is named a gastropod (for class
Gastropoda, the snail class), and this is, at least, a start in
determining the scientific name of that particular fossil. The
descriptive material in the text of each reference will usually point
out the more detailed features which will be diagnostic of the genus or
species.

The illustrations and descriptive material in this publication will also
be of considerable help in identification. Many illustrations of the
more common invertebrate fossils have been included, but the publication
was not designed primarily for use in fossil identification. Rather, it
is intended to guide the amateur or student who is interested in fossil
collecting, and to furnish suggestions as to how collecting may be more
effectively pursued.




                       USE OF IDENTIFICATION KEYS


Fossil identification keys may be useful in helping the beginning
collector identify specimens. The collector compares a fossil with the
key description and eliminates those characters that do not fit the
specimen.

The key used in this handbook is based primarily on _symmetry_—the
orderly arrangement of the parts of an object with reference to lines,
planes, or points. The shape of the shell or body, presence or absence
of coiling, and presence or absence of body partitions are also useful
criteria in identifying fossils. To use the key the beginner should know
something about symmetry. Two major types of symmetry are used in this
key.

  1. _Radial symmetry_—the symmetrical repetition of parts around an
  axis. This is the symmetry of a wheel, and any vertical section
  through the center of the object divides it into symmetrical halves
  (fig. 4a).

  2. _Bilateral symmetry_—the symmetrical duplication of parts on each
  side of a plane (fig. 5). The plane divides the object into two halves
  that are mirror images of each other. This is the symmetry of a plank.

It should be noted that many objects may have both kinds of symmetry.
For example: A cone when viewed from the top has radial symmetry and
when viewed from the side shows bilateral symmetry (fig. 4a, b).

 [Illustration: Fig. 4. Types of symmetry in a fossil coral. (a) Radial
                   symmetry. (b) Bilateral symmetry.]

  [Illustration: Fig. 5. Bilateral symmetry as displayed by a typical
                          fossil brachiopod.]

An illustration of the use of the key on pages 26-27 follows. Assuming
that a specimen displays radial symmetry, this means that it belongs
under Part I on the key. If the fossil has a tapering, cylindrical,
cone-shaped shell (“A” on the key), the subheadings under the “A” part
of the key are examined. Should the specimen have a shell which is
round, tapering at one end, with transverse septa or sutures (number 2
under “A”), it is probably a cephalopod. This is indicated on the right
hand side of the page. Number 1 under “A” is eliminated because the
fossil did not have longitudinal radial partitions within the shell.

Some fossils display no apparent symmetry and such a fossil would be
referred to Part III of the key. If this fossil had internal transverse
partitions “A” would be eliminated. If the fossil was not a coiled
fossil “B” would also be eliminated and we would proceed directly to
“C”—uncoiled fossils. If the specimen is a branching twig-like fossil,
numbers 1, 2, and 3 would be eliminated and the specimen referred to
number 4 (Branching twig-like fossils). Should the specimen have evenly
distributed relatively large openings with radial longitudinal
partitions or septa, the specimen is probably a colonial coral (“b”
under number 4 on the key). The “a” part of number 4 would be eliminated
because the coral had large openings and radial longitudinal septa.

Once a tentative identification has been made from the key, pictures and
descriptions of this fossil group are examined to establish a more
precise identification. It should be remembered that keys are not
perfect, and the collector should not expect to be able to identify
every specimen with this key.




        IDENTIFICATION KEY TO MAIN TYPES OF INVERTEBRATE FOSSILS


(Instructions on pages 23-25 for use of key)

  I. Fossils displaying radial symmetry—symmetrical repetition of parts
          around a central axis
    A. Fossil tapering, cylindrical, cone-shaped:
      1. Fossil with longitudinal radial partitions or septa;
          cone-shaped
                                                                   Coral
      2. Shell with transverse septa or sutures; tapering at one end
                                                              Cephalopod
      3. Shell without internal septa or partitions:
        a. Shell large, heavy; usually with external longitudinal ribs.
            Occur only in Cretaceous rocks
                                                                Rudistid
        b. Shell small (usually less than 2 inches long), tusk-shaped,
            open at both ends. Rare in Paleozoic and Mesozoic rocks
                                                               Scaphopod
    B. Fossil disk-shaped or flattened dome-shaped:
      1. Fossil with radiating star pattern on top
                                                                Echinoid
      2. Fossil subconical to hemispherical, dome-shaped; base concave
          or flat; minute pits or pores covering surface; typically
          small (less than 3 inches across)
                                                                 Bryozoa
      3. Fossil small (less than ½ inch); generally disk-shaped
                                               Foraminifera (orbitoidid)
      4. Fossil disk-shaped or button-like; with longitudinal, radial
          partitions or septa
                                                                   Coral
    C. Fossil composed of segments or plates:
      1. Fossil composed of circular segments, disks, or chambers; when
          united form cylinder:
        a. Tapered shell
                                                              Cephalopod
        b. Non-tapered, segments small and of relatively uniform
            thickness with hole in center; individual columnals
            disk-shaped
                                                            Crinoid stem
      2. Fossil composed of many-sided plates:
        a. Bud-shaped fossil of 13 wedge-shaped plates
                                                                Blastoid
        b. Cup-shaped fossil of many curved plates surrounded by
            branching arms
                                                                 Crinoid
  II. Fossils displaying bilateral symmetry—symmetrical duplication of
          parts on each side of a plane
    A. Fossil coiled in a single plane:
      1. Shell divided by internal transverse partitions or sutures
                                                              Cephalopod
      2. Shell without internal partitions or sutures
                                                               Gastropod
      3. Shell small; spindle-shaped; resembles wheat grain. Common in
          Pennsylvanian and Permian rocks
                                               Foraminifera (fusulinids)
    B. Fossil not coiled:
      1. Shells or valves similar to clams:
        a. Plane of symmetry parallel to hinge; equivalved
                                                               Pelecypod
        b. Plane of symmetry (almost bilaterally symmetrical) at right
            angles to hinge line; mostly inequivalved; strongly ribbed.
            “Scallop-like” with “ears.” Rare in Paleozoic rocks
                                                               Pelecypod
        c. Plane of symmetry at right angles to hinge line;
            inequivalved; not “scallop-like” and without “ears.” Larger
            valve commonly has an opening in beak. Common in Paleozoic
            rocks
                                                              Brachiopod
      2. Fossil tapering, cylindrical, cone-shaped:
        a. Fossil with internal longitudinal, radial septa or
            partitions; cone-shaped
                                                                   Coral
        b. Shell with internal transverse partitions or sutures;
            tapering at one end
                                                              Cephalopod
        c. Shell without internal septa or partitions.
          (1) Shell large, heavy; usually with external longitudinal
              ribs. Occur only in Cretaceous rocks
                                                                Rudistid
          (2) Shell small (usually less than 2 inches), tusk-shaped,
              open at both ends. Rare in Paleozoic and Mesozoic rocks
                                                               Scaphopod
      3. Fossil heart-shaped, domed or flattened; radial star pattern on
          top
                                                                Echinoid
      4. Fossil segmented:
        a. Fossil divided into 3 lobes; may be curled up. Not found in
            Mesozoic or Cenozoic rocks
                                                               Trilobite
        b. Fossil flattened or elongate; resembles shrimp, crab, or
            crayfish
                                                              Crustacean
  III. Fossils displaying no apparent symmetry
    A. Shell without transverse internal partitions or sutures:
      1. Shell coiled like ram’s horn, low spired, opening of shell very
          large; surface has concentric ridges. Shell has two valves;
          smaller, flattened valve not often found. In Texas found only
          in Cretaceous rocks
                                                               Pelecypod
      (Note: Some Paleozoic gastropods, “2,” closely resemble larger
          valve of these pelecypods)
      2. Shell tightly coiled; most have higher spire than “1.” Opening
          of shell smaller than “1”; shell not as rough as “1” and has
          only one valve
                                                               Gastropod
    B. Coiled fossils; coiling not in one plane:
      1. Shell with transverse internal partitions or sutures:
        a. Partitions always smooth; thick shelled; loosely and
            irregularly coiled, usually in large compact masses of many
            individual shells. Occur only in Cretaceous rocks
                                                                Caprinid
        b. Partitions (sutures) usually wrinkled; relatively thin
            shelled; mostly regularly and tightly coiled; occur as
            separate individual specimens
                                                              Cephalopod
      2. Shell without transverse internal partitions or sutures
                                                               Gastropod
      3. Solid spiral ridge around central axis; resembles a corkscrew
                                                                 Bryozoa
    C. Uncoiled fossils:
      1. Fossil resembles a narrow saw blade; typically found as thin
          film of carbon. Not found in Mesozoic or Cenozoic rocks
                                                              Graptolite
      2. Fossil irregularly cone-shaped; longitudinal radial partitions
          or septa
                                                                   Coral
      3. Shell resembles a clam or oyster shell but valve or shell not
          symmetrical
                                              Pelecypod (mostly oysters)
      4. Branching twig-like fossils:
        a. Fossils covered with minute pores or openings
                                                                 Bryozoa
        b. Fossils with evenly distributed, relatively large openings
            with longitudinal radial partitions or septa
                                                          Colonial coral
      5. Lace-like fossils; occur as thin sheets or films
                                                                 Bryozoa
      6. Fossils composed of radiating masses of polygonal or circular
          tubes containing radial septa
                                                          Colonial coral
      7. Irregular fossils; typically cylindrical with rough surface:
        a. Fossil has large axial opening and thick wall; usually has
            external longitudinal ribs. Occurs only in Cretaceous rocks
                                                                Rudistid
        b. Fossil solid with no large axial opening; surface with small
            pits or pores (fewer than in Bryozoa). In Texas, occurs most
            commonly in Pennsylvanian and Permian rocks
                                                                  Sponge




            LIST OF TEXAS COLLEGES OFFERING GEOLOGY COURSES


  A.&M. College of Texas, College Station
  Amarillo College, Amarillo
  Arlington State College, Arlington
  Austin College, Sherman
  Baylor University, Waco
  Blinn College, Brenham
  Corpus Christi, University of, Corpus Christi
  Del Mar College, Corpus Christi
  East Texas State College, Commerce
  Hardin-Simmons University, Abilene
  Henderson County Junior College, Athens
  Houston, University of, Houston
  Howard County Junior College, Big Spring
  Kilgore College, Kilgore
  Lamar State College of Technology, Beaumont
  Lee College, Baytown
  McMurry College, Abilene
  Midwestern University, Wichita Falls
  North Texas State College, Denton
  Odessa College, Odessa
  Pan American College, Edinburg
  Rice University, Houston
  St. Mary’s University, San Antonio
  San Angelo College, San Angelo
  San Antonio College, San Antonio
  Southern Methodist University, Dallas
  South Texas College, Houston
  Southwestern University, Georgetown
  Stephen F. Austin State College, Nacogdoches
  Sul Ross State College, Alpine
  Tarleton State College, Stephenville
  Texarkana College, Texarkana
  Texas Christian University, Fort Worth
  Texas College, Tyler
  Texas College of Arts and Industries, Kingsville
  Texas Technological College, Lubbock
  Texas Western College, El Paso
  The University of Texas, Austin
  Trinity University, San Antonio
  Tyler Junior College, Tyler
  West Texas State College, Canyon

                         [Illustration: Plate 6
                      Fossil Identification Chart
                           I RADIAL SYMMETRY]

  A. Tapering, cylindrical cone-shaped fossils
    1. Cone-shaped with longitudinal partitions or septa
                                                                   Coral
    2. Fossils with septa or sutures; tapering at one end
                                                              Cephalopod
    3. Shell without internal partitions or sutures
      a. Shell large heavy, external longitudinal ribs. Cretaceous only
                                                                Rudistid
      b. Shell small, tusk-shaped open at both ends. Rare in Paleozoic
          and Mesozoic
                                                               Scaphopod
  B. Disc or dome-shaped fossils
    1. Star pattern on top
                                                                Echinoid
    2. Subconical small pits or pores on top
                                                                Bryozoan
    3. Small disc-shaped (less than ½ inch)
                                                   Orbitoid Foraminifera
    4. Disc-shaped or button-like, with longitudinal partitions or septa
                                                                   Coral
  C. Fossils composed of segments or plates
    1. Circular discs or chambers; when united form cylinder
      a. Tapered shell
                                                              Cephalopod
      b. Not tapered, segments small of uniform thickness, hole in
          center
                                                            Crinoid Stem
    2. Fossil composed of many-sided plates
      a. Bud-shaped, 13 wedge-shaped plates
                                                                Blastoid
      b. Cup-shaped, many curved plates branching arms
                                                                 Crinoid

                         [Illustration: Plate 7
                      Fossil Identification Chart
                         II BILATERAL SYMMETRY]

  A. Fossil coiled in a single plane
    1. Shell divided by internal transverse partitions or sutures
                                                              Cephalopod
    2. Shell without internal partitions or sutures
                                                               Gastropod
    3. Shell small, spindle-shaped; resembles wheat grain. Pennsylvanian
          and Permian
                                                  Foraminifera fusulinid
  B. Fossil not coiled
    1. Shells or valves similar to clams
      a. Plane of symmetry parallel to hinge; equivalved
                                                               Pelecypod
      b. Plane of symmetry almost at right angles to hinge; strongly
          ribbed; “Scallop-like” with “ears”, inequivalved
                                                               Pelecypod
      c. Plane of symmetry at right angles to hinge-line; without
          “ears”, not “Scallop-like”; commonly with opening in beak,
          inequivalved
                                                              Brachiopod
    2. Fossil tapering, cylindrical or cone-shaped
      a. Cone-shaped, internal longitudinal partitions or septa
                                                                   Coral
      b. Tapered, internal transverse partitions
                                                              Cephalopod
      c. Shell without internal septa or partitions
        (1.) Shell large heavy, longitudinal ribs. Cretaceous only
                                                                Rudistid
        (2.) Shell small, tusk-shaped, open at both ends, rare in
            Paleozoic and Mesozoic rocks
                                                               Scaphopod
    3. Fossil heart-shaped, domed or flattened; star pattern on top
                                                                Echinoid
    4. Fossil segmented
      a. Divided into 3 lobes, may be curled up. Paleozoic only
                                                               Trilobite
      b. Flattened or elongate, resembles shrimp
                                                              Crustacean

                         [Illustration: Plate 8
                      Fossil Identification Chart
                       III NO APPARENT SYMMETRY]

  A. Shell without transverse partitions or sutures
    1. Shell coiled like ram’s horn, low spired; shell has two valves,
          smaller flattened valve often missing. In Texas exclusively
          Cretaceous
                                                               Pelecypod
    2. Shell tightly coiled, most have higher spire than 1, shell
          smaller and not as rough as 1, has only one valve
                                                               Gastropod
  B. Coiled fossils, coiling not in one plane
    1. Shell with transverse internal partitions or sutures
      a. Partitions always smooth, thick shelled, loosely and
          irregularly coiled, in Texas exclusively Cretaceous
                                                                Caprinid
      b. Partitions (sutures) generally wrinkled, regularly and tightly
          coiled
                                                              Cephalopod
    2. Shell without transverse internal partitions or sutures
                                                               Gastropod
    3. Solid spiral ridge around central axis, resembles corkscrew
                                                                Bryozoan
  C. Uncoiled fossils
    1. Fossil resembles narrow saw blade. Paleozoic only
                                                              Graptolite
    2. Fossil irregularly cone-shaped, longitudinal partitions or septa
                                                                   Coral
    3. Shell resembles clam or oyster, nonsymmetrical
                                              Pelecypod (mostly oysters)
    4. Branching twig-like fossils
      a. Covered with minute pores or openings
                                                                 Bryozoa
      b. With evenly distributed larger openings with septa
                                                          Colonial coral
    5. Lace-like fossils, occur as thin sheets or films
                                                                 Bryozoa
    6. Masses of circular or polygonal tubes with septa
                                                          Colonial coral
    7. Irregular fossils, cylindrical with rough surface
      a. Large axial opening with thick wall, external longitudinal
          ribs. Cretaceous only
                                                                Rudistid
      b. Solid, no opening, small pits or pores. Pennsylvanian or
          Permian
                                                                  Sponge




                       CATALOGING THE COLLECTION


After the fossils have been cleaned and tentatively identified, they
should be cataloged. This is necessary to enable the collector to have a
record of his collection and to furnish as much information as possible
about each individual fossil.

The collecting data can be taken from the labels that were placed in
each bag of fossils as they were collected, or from the field notebook.
Actually, it is wise to check one against the other. This information
should then be entered in some type of record book and also placed on a
more permanent label which is put in the tray or box with the fossil.
The catalog and label should contain such pertinent data as (1) the
scientific name of the fossil, (2) the geologic formation from which the
specimen was collected, (3) the exact geographic location of the
collecting locality, (4) the name of the collector, (5) the date the
fossil was collected, and (6) the catalog number of the specimen. The
latter is usually placed in the upper right hand corner of the label
(fig. 6) and corresponds with a like number in the record book.




  Specimen No. P-185
  NAME Spirifer rockymontanus
  FORMATION Big Saline (Penn.)
  LOCALITY Little Brady Creek, McCulloch Co., Tex.
          (1000′ NE of Smith ranch House)
  COLLECTOR F. B. Plummer
  DATE July 1937

 [Illustration: Fig. 6. A brachiopod showing the catalog number on it,
       and the accompanying label that pertains to the specimen.]

The entries in the catalog should be numbered consecutively, and all
specimens from the same locality should bear the same number. This
number should be written on the fossil with India ink, preferably on any
remaining matrix or on some inconspicuous part of the specimen (fig. 6).
If the surface of the fossil is too coarse or porous for ink, the
catalog number can be written on a small patch of white enamel or clear
nail polish painted on the specimen. After the ink has dried it should
be coated with a dab of clear shellac or clear nail polish to help
preserve the number. If each specimen is numbered, it can easily be
identified even if it should become separated from its label.




                          HOW FOSSILS ARE USED


Fossils are useful in a number of different ways, for each specimen
provides some information about when it lived, where it lived, and how
it lived.

Fossils are very important, for example, in tracing the development of
the plants and animals of our earth. This is possible because the
fossils in the older rocks are usually primitive and relatively simple;
but a study of similar specimens that lived in later geologic time shows
that the fossils become progressively more complex and more advanced in
the younger rocks.

Some fossils, for example, the reef-building corals, appear to have
always lived under much the same conditions as they live today. Hence,
it is reasonably certain that the rocks containing fossil reef corals
found in place (that is, where they were originally buried), were
deposited in warm, fairly shallow, salt water. By studying the
occurrence and distribution of such marine fossils, it is possible to
outline the location and extent of prehistoric seas. Moreover, the type
of fossils present will frequently give some indication as to the bottom
conditions, depth, temperature, and salinity of these ancient bodies of
water.

Probably the most important use of fossils is for purposes of
_correlation_—the process of demonstrating that certain rock layers are
closely related to each other. By correlating or “matching” the beds
containing specific fossils, it is possible to determine the
distribution of geologic units of similar age. Some fossils have a very
limited vertical or geologic range and a wide horizontal or geographic
range. In other words, they lived but a relatively short period in
geologic time but were rather widely distributed during their relatively
short life. Such fossils are known as _index fossils_ or _guide fossils_
and are especially useful in correlation because they are normally only
associated with rocks of one certain age.

  [Illustration: Fig. 7. Sketches of two types of micropaleontological
    slides. (a) Multiple space faunal slide. (b) Single-hole slide.]

Microfossils are often very valuable as guide fossils for the petroleum
geologist. The micropaleontologist washes the well cuttings from the
drill hole and separates the tiny fossils from the surrounding rocks.
The specimens are then mounted on special slides (fig. 7) and studied
under the microscope. Information derived from these fossils often
provides valuable data on the age of the subsurface formation and the
possibilities of oil production. Microfossils are particularly valuable
in the oil fields of the Gulf Coast region of Texas. In fact, some of
the oil-producing zones in this area have even been named for certain
key genera of microfossils. For example, the “het” zone of Oligocene age
(geologic time scale, Pl. 1) is named for the genus _Heterostegina_,
which is a tiny one-celled animal. Other microfossils, such as
fusulinids, ostracodes, spores, and pollens, are also used to identify
subsurface formations in many other parts of the State.

Plant fossils are very useful as climatic indicators but are not too
reliable for purposes of age determination. They do, however, provide
much information about the development of plants throughout geologic
time.




                            GEOLOGIC HISTORY


The geologic history of our earth has been recorded primarily in marine
sedimentary rocks, and this record indicates that our earth is very old
and that life has been present for many millions of years. The earth is
not only extremely old (more than 3½ billion years of age), but it has
also undergone many changes which have taken place slowly but steadily
and have greatly affected both the earth and its inhabitants. The
earth’s physical features have not always been as they are seen today.
Geologic research has shown that mountains now occupy the sites of
ancient seas, and that coal is being mined where swamps existed millions
of years ago. Furthermore, there is much evidence to indicate that
plants and animals have also undergone great change. The trend of this
organic change is, in general, toward more complex and advanced forms of
life, but some forms have remained virtually unchanged and others have
become extinct.

In order to interpret geologic history, the earth scientist must attempt
to gather evidence of the great changes in climate, geography, and life
that took place in the geologic past. The record of these changes can be
found in the rocks, and here is found the story of the various events in
earth history.




                     GEOLOGIC COLUMN AND TIME SCALE


In order to discuss fossils and the age of the rocks containing them, it
is necessary to become familiar with the _geologic column_ and the
_geologic time scale_ (Pl. 1).

The _geologic column_ refers to the total succession of rocks, from the
oldest to most recent, that are found either locally or in the entire
earth. Thus, the geologic column of Texas includes all rock divisions
known to be present in this State. By referring to the geologic column
previously worked out for any given area, the geologist can determine
what type of rocks he might expect to find in that particular region.

The _geologic time scale_ is composed of units which represent intervals
of geologic time, during which were deposited the rocks represented in
the geologic column. These time units are used by the geologist to date
the events that have taken place in the geologic past.

The largest unit of geologic time is an era, and each era is divided
into smaller time units called _periods_. A period of geologic time is
divided into _epochs_, which, in turn, may be subdivided into still
smaller units. The geologic time scale might be roughly compared to the
calendar in which the year is divided into months, months into weeks,
and weeks into days. Unlike years, however, geologic time units are
arbitrary and of unequal duration, and the geologist cannot be positive
about the exact length of time involved in each unit. The time scale
does, however, provide a standard by which he can discuss the age of
fossils and their surrounding rocks. By referring to the time scale it
may be possible, for instance, to state that a certain event occurred
during the Paleozoic era in the same sense that one might say that
something happened during the American Revolution.

There are five eras of geologic time, and each has been given a name
that is descriptive of the degree of life development that characterizes
that era. Hence, Paleozoic means “ancient-life,” and the era was so
named because of the relatively simple and ancient stage of life
development.

The eras, a guide to their pronunciation, and the literal translation of
each name is shown below.

  Cenozoic (SEE-no-zo-ic)—“recent-life”
  Mesozoic (MES-o-zo-ic)—“middle-life”
  Paleozoic (PAY-lee-o-zo-ic)—“ancient-life”
  Proterozoic (PRO-ter-o-zo-ic)—“primitive-life”
  Archeozoic (AR-kee-o-zo-ic)—“beginning-life”

Archeozoic and Proterozoic rocks are commonly grouped together and
referred to as Precambrian in age. The Precambrian rocks have been
greatly contorted and metamorphosed, and the record of this portion of
earth history is most difficult to interpret. Precambrian time
represents that portion of geologic time from the beginning of earth
history until the deposition of the earliest fossiliferous Cambrian
strata. If the earth is as old as is believed, Precambrian time may
represent as much as 85 percent of all geologic time.

The _oldest_ era is at the _bottom_ of the list because this part of
geologic time transpired first and was then followed by the successively
younger eras which are placed above it. Therefore, the geologic time
scale is always read _from the bottom of the chart upward_. This is, of
course, the order in which the various portions of geologic time
occurred and during which the corresponding rocks were formed.

As mentioned above, each of the eras has been divided into periods, and
most of these periods derive their names from the regions in which the
rocks of each were first studied. For example, the Pennsylvanian rocks
of North America were first studied in the State of Pennsylvania.

The Paleozoic era has been divided into seven periods of geologic time.
With the oldest at the bottom of the list, these periods and the source
of their names are:

  Permian (PUR-me-un)—from the Province of Perm in Russia
  Pennsylvanian (pen-sil-VAIN-yun)—from the State of Pennsylvania
  Mississippian (miss-i-SIP-i-un)—from the Upper Mississippi Valley
  Devonian (de-VO-ni-un)—from Devonshire, England
  Silurian (si-LOO-ri-un)—for the Silures, an ancient tribe of Britain
  Ordovician (or-doe-VISH-un)—for the Ordovices, an ancient tribe of
          Britain
  Cambrian (KAM-bri-un)—from the Latin word _Cambria_, meaning Wales

The Carboniferous period in Europe includes the Mississippian and
Pennsylvanian periods of North America. Although this classification is
no longer used in the United States, the term Carboniferous will be
found in many of the earlier geological publications and on many of the
earlier geologic maps.

The periods of the Mesozoic era and the source of their names are:

  Cretaceous (cre-TAY-shus)—from the Latin word _creta_, meaning chalky
  Jurassic (joo-RAS-ik)—from the Jura Mountains of Europe
  Triassic (try-ASS-ik)—from the Latin word _triad_, meaning three

In Texas, the Cretaceous has two divisions, known as either Lower
Cretaceous and Upper Cretaceous or as Comanche series and Gulf series,
respectively. These designations are for rocks of nearly equivalent age,
and both sets of terms have been used by geologists and in publications.
In this handbook, both sets of terms are used interchangeably, that is,
Lower Cretaceous and/or Comanche series and Upper Cretaceous and/or Gulf
series.

The Cenozoic periods derived their names from an old outdated system of
classification which divided all of the earth’s rocks into four groups.
The two divisions listed below are the only names of this system which
are still in use:

  Quaternary (kwah-TUR-nuh-ri)
  Tertiary (TUR-shi-ri)

While the units discussed above are the major divisions of geologic
_time_, the geologist usually works with smaller units of _rocks_ called
_formations_. A geologic formation is identified and established on the
basis of definite physical and chemical characteristics of the rocks.
Formations are usually given geographic names which are combined with
the type of rock that makes up the bulk of the formation. For example,
the Beaumont clay was named from clay deposits that are found in and
around Beaumont, Texas.




                          THE GEOLOGY OF TEXAS


The geologic history of Texas, like the geologic history of the rest of
the earth, is recorded primarily in marine sedimentary rocks. These
rocks provide some knowledge of the early geography and the first
inhabitants of what is now the State of Texas. Most of these rocks were
formed from sediments deposited in shallow seas which covered parts of
the State at various times in earth history.

By studying these rocks and their relations to each other, geologists
have established a geologic column for Texas.


                              Physiography

In order to discuss the distribution and exposures of the rocks of
Texas, it is helpful to be familiar with the _physiography_ of the
State. Physiography deals with the study of the origin and description
of land forms, such as mountains, valleys, and plains. Plate 9 is a map
of Texas which shows the major physiographic provinces within the State.

The majority of the land forms in Texas have been produced by the
processes of erosion attacking the structural features of an area.
Certain other land forms may be related to the effects of igneous
activity which resulted in the accumulation of large masses of igneous
rocks. The Davis Mountains are an example of surface features produced
in this manner.

In discussing the physiography of Texas, three major physiographic
provinces will be recognized. These are (1) the Trans-Pecos region, (2)
the Texas Plains, and (3) the Gulf Coastal Plain (Pl. 9).


                           TRANS-PECOS REGION

The Trans-Pecos region, located in the westernmost part of the State, is
an area of mountains and plateaus with broad basins between the major
mountain ranges. Many different types of rocks are exposed in
Trans-Pecos Texas and these include marine, fresh-water, and terrestrial
deposits. In many areas igneous rocks flowed out on the surface and now
overlie sedimentary rocks. There are also many places where igneous
rocks have been injected into the surrounding rocks, and these igneous
rocks have been exposed by later erosion.

Included within this area is the Van Horn uplift of southern Hudspeth
and Culberson counties, the Solitario uplift of southern Presidio and
Brewster counties, and the Marathon uplift of northeast Brewster County.
This region also includes the Big Bend area of Texas, a part of which
has been set aside as a National Park where many interesting and
important geological features may be seen.

The Trans-Pecos region is one of rugged topography with elevations as
high as 8,700 feet, at Guadalupe Peak in the Guadalupe Mountains of
northern Culberson County, and as low as 1,500 feet, in the Rio Grande
valley.

Numerous invertebrate fossils occur in the Cretaceous limestones and
shales of the Trans-Pecos region and in the Paleozoic rocks of the
Marathon uplift. The Gaptank formation of Pennsylvanian age and the
Permian reef limestones of the Glass Mountains are especially
fossiliferous. In addition, many vertebrate fossils have been collected
in Trans-Pecos Texas, particularly in and around Big Bend National Park.


                              TEXAS PLAINS

The plains of Texas are broad expanses of country with very little
surface relief. Most of the plains support grasses and some have wooded
areas, particularly along stream valleys.

The plains of the northwestern part of the State have been subdivided as
follows.


                              High Plains

This area (Pl. 9), often called “the caprock,” is an elevated plateau
which rises above the rolling plains which surround it. The High Plains
are bounded by the Pecos River valley on the south, southeast, and west
and by the North-Central Plains on the east.

The surface of the High Plains is very flat and characterized by a
sparse cover of grasses and few trees. The surface strata consist
largely of unconsolidated deposits of sands and gravels of Quaternary
and Tertiary age, with remnants of Lower Cretaceous limestones along the
southern margin. The rocks of the High Plains are mostly
unfossiliferous, but mammalian remains have been found at several
localities.

                         [Illustration: Plate 9
                      Physiographic map of Texas.]

  HIGH PLAINS
  NORTH-CENTRAL PLAINS
  GRAND PRAIRIE
  TRANS-PECOS TEXAS
  VAN HORN UPLIFT
  THE BIG BEND AREA
  SOLITARIO UPLIFT
  MARATHON UPLIFT
  EDWARDS PLATEAU
  LLANO UPLIFT
  BALCONES FAULT ZONE
  GULF COASTAL PLAIN


                          North-Central Plains

Surface strata of the North-Central Plains (Pl. 9) are westward-dipping
Pennsylvanian, Permian, and Triassic rocks. Present also are extensive
exposures of Quaternary sands and gravels which trend north-south across
the central portion of the region. The area is bounded on the west by
the High Plains, on the east by the Grand Prairie, and on the south by
the Edwards Plateau and Llano uplift. Many vertebrate fossils have been
collected from the Permian and Triassic rocks of this area. There are
also many excellent outcrops of fossiliferous Pennsylvanian formations
in the North-Central Plains region.


                            Edwards Plateau

The Edwards Plateau (Pl. 9) is located in south-central Texas and is
bounded on the south by the Balcones fault zone and on the north by the
North-Central Plains. The surface of the area is typically flat with a
gentle slope to the south. The rocks of the Edwards Plateau consist
primarily of Lower Cretaceous limestones and shales, many of which are
very fossiliferous.


                             Grand Prairie

This area (Pl. 9) has a relatively flat surface but there are areas of
gently rolling hills. The eastern boundary of the Grand Prairie is
marked partly by the Balcones fault zone. North of McLennan County,
however, the Balcones fault zone is not expressed at the surface and in
this area the eastern boundary is defined by the western edge of the
Woodbine exposures. Upper and Lower Cretaceous rocks occur at the
surface and dip to the southeast; many of these rocks contain a large
number of invertebrate fossils.


                              Llano Uplift

The Llano uplift (Pl. 9) is located in the central part of the State
where Precambrian igneous and metamorphic rocks and sedimentary rocks of
early Paleozoic age occur on the surface. The area, which now appears as
a basin-shaped depression, was at one time covered by Lower Cretaceous
rocks and perhaps also by Devonian, Mississippian, and Pennsylvanian
strata. These have since been removed by erosion. The east, south, and
west sides of the uplift are surrounded by Lower Cretaceous rocks, and
the northern margin is marked by the Mississippian and Pennsylvanian
formations of the North-Central Plains. The area is, in general,
composed of unfossiliferous rocks, but some invertebrate fossils
(primarily trilobites and brachiopods) have been collected.


                           GULF COASTAL PLAIN

The Gulf Coastal Plain (Pl. 9) is composed of Cretaceous, Tertiary, and
Quaternary rocks and includes the eastern, southeastern, and southern
portions of the State. The rocks of the area consist of sands, clays,
shales, and limestones. The Texas Gulf Coastal Plain is bounded on the
north and west by the Balcones fault zone, on the south and southwest by
the Gulf of Mexico, and extends eastward into Arkansas and Louisiana.

The region has broad river valleys and uplands of low relief, but there
is an increase in relief toward the interior of the State. The surface
of the area slopes gradually toward the Gulf and successively younger
formations are encountered gulfward.

The rocks of the Texas Gulf Coastal Plain are relatively
unfossiliferous, but many of the Upper Cretaceous rocks contain fossils.
In the central portion of the region some marine formations of Tertiary
age locally contain well-preserved invertebrate fossils.




                                Geology


Geologic studies of the State of Texas have indicated the presence of
rocks formed during every era and period of geologic time. These range
from the Precambrian granites of the Llano uplift to the Quaternary
gravels of the High Plains.

                        [Illustration: Plate 10
                   GENERALIZED GEOLOGIC MAP OF TEXAS
               Modified from Geologic Map of Texas, 1933]

One of the best ways to become acquainted with the geology of Texas is
to study the _geologic map_ of the State (Pl. 10). A geologic map shows
the distribution and age of surface rocks and may also indicate what
kind of geologic structures are present. The types of rocks that crop
out at the surface may be shown by means of symbols, colors, or
patterns, and these are explained by a legend which accompanies the map.
On Plate 10, colors are used to show the distribution and geologic age
of the surface rocks of Texas. Reference to this map will give the
collector some idea of the age of the fossils that might be found in a
given area. Some special geologic maps may have the location of geologic
structures and formation contacts indicated by means of symbols, such as
dashed lines, arrows, and similar special markings. However, the map
included in this publication does not show any of these special
markings.


                           PRECAMBRIAN ROCKS

The Precambrian rocks of Texas are composed of igneous and metamorphic
rocks and some sedimentary rocks. Most of the Precambrian outcrops are
in the Llano uplift and El Paso and Van Horn regions.

Alterations produced by vast amounts of time, heat, and pressure have
obliterated any trace of fossils that may have been present in these
rocks. With the exception of some questionable primitive plants
collected in the Van Horn region, no Precambrian fossils have been
reported from Texas.


                            PALEOZOIC ROCKS

Rocks of Paleozoic age are widespread in Texas, and rocks of each period
are well exposed. Outcrops are found in the Llano uplift, North-Central
Plains, and Trans-Pecos region. The most extensive exposures are of
Pennsylvanian and Permian age, and the former are highly fossiliferous
in parts of the North-Central Plains.

                                Cambrian

Rocks of late Cambrian age are exposed in the Llano, Marathon, and
Solitario uplifts, and the Franklin Mountains near El Paso. These are
sedimentary rocks consisting of conglomerates, sandstones, shales,
limestones, and some dolomites.

Some of these formations are relatively fossiliferous, but the specimens
are commonly fragmental and very poorly preserved. Fossils that are apt
to be found in the Cambrian rocks of the Llano uplift include
brachiopods, gastropods, trilobites, and small rounded objects believed
to have been formed by algae (primitive one-celled plants). In other
parts of the State, Cambrian rocks are sparsely fossiliferous and the
fossils consist primarily of fragmental brachiopods, trilobites, and
algae.

                               Ordovician

Ordovician outcrops are present in the Llano uplift of central Texas and
in the Marathon, Solitario, El Paso, and Van Horn regions of Trans-Pecos
Texas. These are sedimentary rocks and consist largely of sandstones,
cherts, limestones, and dolomites.

Although some of the Ordovician formations are fossiliferous, they are
seldom collected by amateur paleontologists because they are exposed in
relatively inaccessible places and the fossils are usually poorly
preserved. Ordovician fossils reported from Texas include sponges,
corals, brachiopods, gastropods, cephalopods, and trilobites. In
addition, the Marathon formation of the Marathon uplift contains large
numbers of well-preserved graptolites (fig. 24, p. 86).

                                Silurian

The Silurian of Texas is poorly represented in surface exposures, and
only one formation, the Fusselman, has been described. The Fusselman
crops out in the El Paso and Van Horn regions where it is a white
dolomitic limestone. Fossils are not abundant in this formation, but
brachiopods and corals have been collected at a few localities.

                                Devonian

Devonian rocks are best developed in Trans-Pecos Texas, especially in
the Marathon, El Paso, and Van Horn regions. In addition to the
Trans-Pecos exposures, there are minor outcrops of Devonian rocks in the
Llano uplift of central Texas.

Fossils are rare and fragmental in the Trans-Pecos exposures and consist
primarily of radiolarians and brachiopods. The Devonian rocks of central
Texas are predominantly calcareous and, although the material is usually
poorly preserved, many fossils have been collected from them. These
include bryozoans, corals, brachiopods, gastropods, and trilobites.
Conodonts and fragments of primitive armored fishes (Pl. 37) have also
been reported.

                             Mississippian

Mississippian rocks are exposed in the Llano region and in the Hueco
Mountains of the Trans-Pecos area. The Trans-Pecos rocks primarily
contain brachiopods with some bryozoans and gastropods.

The central Texas Mississippian rocks are much more fossiliferous and
some of the material is well preserved. Fossils reported from this area
include brachiopods (Pl. 17), crinoids, gastropods, cephalopods,
trilobites, and ostracodes.

                             Pennsylvanian

Pennsylvanian rocks are well represented in Texas and are exposed in the
Llano uplift, north-central Texas, and Trans-Pecos Texas.

In Trans-Pecos Texas fossiliferous rocks crop out in the Hueco and
Diablo Mountains. Fossils found in this area are algae, fusulinids,
corals, brachiopods, pelecypods, gastropods, cephalopods, and crinoids.
There is also a thick section of Pennsylvanian rocks in the Marathon
uplift, but only one formation, the Gaptank, is very fossiliferous. It
contains many fossils including fusulinids, sponges, corals, bryozoans,
brachiopods, gastropods, pelecypods, cephalopods, and crinoids.

Certain Pennsylvanian strata in the Llano region are very fossiliferous,
and the material is well preserved. The more abundant forms are
fusulinids, corals, brachiopods, gastropods, pelecypods, cephalopods,
and crinoids.

Probably the best Pennsylvanian collecting areas are to be found in
north-central Texas. Here the thick marine limestones and shales contain
large numbers of well-preserved invertebrate fossils, and the
terrestrial or shallow marine strata have yielded an abundance of plant
fossils. Invertebrate fossils are apt to be found along the banks of
streams and gullies and in railroad and highway cuts. Many of the
limestones bear large numbers of fusulinids or crinoid stems, and the
shales may contain many corals, brachiopods, and mollusks. The best
collecting will, of course, be found where the rocks have been
sufficiently weathered.

 [Illustration: Fig. 8. Sketch of typical crinoidal limestone from the
                     Pennsylvanian of north Texas.]

Typical invertebrate fossils are foraminifera (principally fusulinids),
corals (especially the solitary or “horn” corals), brachiopods,
bryozoans (the lacy and branching types are most common), pelecypods,
gastropods (exhibiting a variety of coiling), cephalopods (nautiloids
and goniatites predominate), and crinoids, which in many areas are found
in thick crinoidal limestones (fig. 8). Some typical Pennsylvanian
fossils are illustrated in Plates 14, 15, 17, 18, 19, 20, 21, 24, 32,
and 35.

                                Permian

Permian rocks are found in widely separated areas in Texas. The best
exposed section of marine Permian rocks is found in the Glass Mountains
of Brewester County, and many of these rocks are very fossiliferous. The
original shell material of some of the Permian fossils of this area has
been replaced by siliceous material which is very well preserved. These
silicified fossils are removed from the limestone by solution in acid,
and some most remarkable specimens have been recovered in this manner
(Pl. 3). Brachiopods are the most common fossils, but corals, bryozoans,
and mollusks have also been recovered.

Extensive Permian exposures occur also in the central part of the
North-Central Plains region. These rocks were formed from sediments of
both marine and continental origin and some of them are fossiliferous.
The marine rocks contain a variety of invertebrate fossils including
brachiopods, pelecypods, gastropods, and ammonoids. Those rocks
representing terrestrial deposits contain vertebrate remains at many
localities, and numerous amphibians and primitive reptiles (Pl. 40) have
been collected from them.


                             MESOZOIC ROCKS

Mesozoic rocks occur over a wide area of Texas and include exposures of
Triassic, Jurassic, and Cretaceous age. Many of the Upper and Lower
Cretaceous outcrops are quite fossiliferous and easily accessible and
thus of considerable interest to many amateur collectors.

                                Triassic

Triassic rocks crop out in parts of the High Plains, the Glass Mountains
of Trans-Pecos Texas, and parts of Pecos, Crockett, Upton, Reagan, and
Glasscock and other west Texas counties. These are predominantly
nonmarine rocks consisting of conglomerates, sandstones, shales, and
some gypsum beds.

Triassic fossils are almost exclusively vertebrates, although some
poorly preserved plant and invertebrate remains have been reported.
Fossil vertebrates of the Texas Triassic include phytosaurs (Pl. 42),
crocodiles, amphibians, and fish.

                                Jurassic

In Texas, surface exposures of Jurassic rocks are known only from Malone
Mountain in southwestern Hudspeth County. The rocks there are
limestones, shales, sandstones, and conglomerates. Fossils reported from
that locality include marine and fresh-water pelecypods, fresh-water
gastropods, and ammonites.

                               Cretaceous

Rocks of Cretaceous age are widely distributed in Texas and represent
one of the more important rock systems of the State. Cretaceous outcrops
occur in central Texas, north Texas, the Edwards Plateau, parts of the
High Plains, the Gulf Coastal Plain, and Trans-Pecos Texas.

As mentioned earlier, the Texas Cretaceous has been divided into the
Lower Cretaceous (Comanche series) and Upper Cretaceous (Gulf series).
These rocks consist primarily of marls (a type of calcareous clay),
shales, chalks, and limestones, but sands and conglomerates also occur.
Cretaceous rocks occur on the surface of about 28 percent of Texas, and
many of the larger cities of the State are situated on Cretaceous
strata.

Many of the Gulf and Comanche formations contain fossils which are of
interest both to amateur and professional paleontologists. Because of
their wide distribution in and near large population centers, Cretaceous
outcrops can be conveniently visited by many amateur fossil collectors.
The fossils are usually abundant and varied, and some are well
preserved. Although numerous kinds of fossils may be collected, the more
common forms are cephalopods, pelecypods, gastropods, and echinoids.
Some of the more typical Cretaceous fossils are shown in Plates 16, 21,
25-28, 32, 33, 35, and 36.

Cretaceous fossils are more commonly found in shales and chalky
limestones. Fossiliferous outcrops of these rocks can be found along
many streams, roads, and highways of central Texas, north Texas, and the
Edwards Plateau. Outcrops which have been weathered are more likely to
provide good collecting. In general, collecting is poor in areas covered
with heavy vegetation or recent stream deposits. Good collecting
localities are outcrops which have a fairly steep slope with a covering
of weathered rock material and a minimum of vegetation. One should move
slowly from the base of the slope upward while searching the ground for
any evidence of fossils, and particular attention should be given to any
small gullies since these often contain fossils that have been washed
out of upper beds in the exposure.


                             CENOZOIC ROCKS

Cenozoic rocks are widespread in Texas but occur primarily in a broad
belt along the Gulf Coastal Plain. In addition, there are exposures of
nonmarine Cenozoic strata in the High Plains, North-Central Plains, and
Trans-Pecos region. There are also many exposures of Cenozoic igneous
rocks in Trans-Pecos Texas.

Rocks of Cenozoic age occur in more than one-third of Texas and consist
of conglomerates, sands, clays, and some limestone and lignite beds.


                                Tertiary

Extensive exposures of Tertiary rocks trend northeast-southwest in a
broad band across the Gulf Coastal Plain area. These strata, consisting
of sands, clays, and poorly consolidated limestones, are underlain by
Cretaceous rocks.

Invertebrate fossils are common in certain Tertiary formations and
pelecypods, gastropods, and corals are the predominant forms. In
general, however, fossiliferous exposures are of local occurrence and
most of the Tertiary formations are unfossiliferous. Those Tertiary
invertebrates that are present, however, are often well preserved and
represent many interesting types (Pls. 16, 22, 23, 29, 30, 31).

Tertiary invertebrate fossils are commonly found in sands, clays, and
marls. Many of these sands and marls have a green color which is due to
the presence of glauconite (a green mineral containing iron and closely
related to the micas). At certain localities on the Gulf Coastal Plain
the glauconite marls and sands of the Weches and Crockett formations
contain large numbers of well-preserved clams, snails, and corals.
Fossiliferous exposures of Tertiary rocks are sometimes found in road
cuts, but better exposures may be found along the banks of rivers and
creeks. Certain bluffs along the Brazos, Sabine, and Trinity rivers are
well-known Tertiary fossil collecting localities. Many of these better
localities are listed in some of the Bureau of Economic Geology
bulletins included in the bibliography of this publication (pp.
109-110).


                               Quaternary

Quaternary deposits of Pleistocene age (geologic time scale, Pl. 1) are
found in many parts of Texas and consist of sands, clays, and gravels.

These rocks are distributed along the Gulf Coast in a belt from 50 to
100 miles wide. They occur also as stream terraces in the Edwards
Plateau and North-Central Plains regions. In addition, Quaternary sands
and gravels are widely distributed over the surface of much of
Trans-Pecos Texas. There are also fossiliferous Pleistocene strata in
the High Plains region.

Invertebrate fossils are rare in Pleistocene rocks, but some fresh-water
and terrestrial mollusks occur. Vertebrate remains, however, are
abundant in many localities, and large numbers of horses, camels,
mammoths, and other mammals (Pls. 46-49) have been collected. Fossil
bones and teeth (figs. 25, 26, p. 104) are commonly found in the gravels
and sands of many of the river terraces of the State.




                         MAIN TYPES OF FOSSILS


The beginning fossil collector is usually amazed by the many different
plants and animals that have left some trace of their existence. In
order to understand these different types of prehistoric life, it is
necessary to know something about the organisms that are living today.

This handbook discusses the more important groups of plants and animals
which have left some sort of paleontological record, and each major
group begins with a discussion of the more simple organisms and
continues through the more advanced forms. Because scientific workers do
not always agree on exactly the same classification, the system adopted
in this handbook contains the latest ideas of several workers. It is
simple enough to understand, yet complete enough to help one know and
classify his fossils. It should be noted that this classification may
differ in some respects from that of certain older paleontological
publications. Therefore, it has seemed advisable to list other names for
some of the groups that are discussed.

In some instances, the brief descriptions and illustrations of each
group will enable the collector to make a preliminary identification of
his fossils. For more detailed information about each group, the reader
should refer to “Books About Fossils” (pp. 108-110).

This part of the handbook begins with a brief summary of the major
groups of the plant kingdom, followed by a discussion of the
characteristics and relative paleontological importance of the various
invertebrate animals. Emphasis is placed on the invertebrates because
this type of fossil is most commonly collected by the amateur. Finally,
there is a general review of the vertebrates.




                             PLANT FOSSILS


Plant fossils are usually fragmental and poorly preserved, and this
tends to discourage most amateurs from an active interest in
paleobotany. However, in spite of these problems, much is known of the
evolution of plants, and plant fossils provide much information about
life of the past. In addition, certain plants are of considerable value
as indicators of ancient climatic conditions, and their remains have
played a large part in the formation of vast coal deposits.


                  Classification of the Plant Kingdom

In the following classification only the larger taxonomic groups are
discussed. Notice that the term _division_ has been used in place of the
term phylum as used in the animal kingdom. This usage is now preferred
by many botanists and paleobotanists.

                          DIVISION THALLOPHYTA

Thallophytes are simple plants without roots, stems, or leaves. They
include the fungi, algae, and diatoms (Pl. 12). Diatoms are microscopic
fossils that are found in many of the rocks of Texas, and they are quite
abundant in Recent sediments as well. Certain of the Paleozoic
limestones of central Texas contain banded spherical masses of algae
called “algal biscuits.” Although not particularly useful fossils,
thallophytes have a long geologic history and are known in rocks ranging
from Precambrian to Recent in age.

                           DIVISION BRYOPHYTA

The bryophytes are simple rootless plants and include the mosses and
liverworts. Although more complex, the bryophytes resemble the algae in
some respects. They are uncommon fossils, but undoubted bryophytes
(liverworts) have been reported from rocks as old as Mississippian.

                         DIVISION TRACHEOPHYTA

This division has been divided into four subdivisions, among which are
many of the more common living and fossil plants. Such important plants
as the ferns, evergreens, hardwood trees, and the flowering plants are
all tracheophytes. Among the more common and abundant fossil
tracheophytes are the ferns, cycads, and _Gingko_, in addition to such
important “coal plants” as the scale trees, club mosses, and scouring
rushes (Pls. 12, 13). The latter commonly occur in many of the world’s
great coal deposits, and their remains make up a large part of the coal.
Plant fossils of this type may be collected in the dumps around some of
the abandoned coal mines in north-central Texas and from other
Pennsylvanian rocks in north and Trans-Pecos Texas.

                        [Illustration: Plate 11
        GEOLOGIC RANGE OF THE MAJOR GROUPS OF PLANTS AND ANIMALS
   The bands give some indication of the geologic range and relative
abundance of the major groups of plants and animals. An increase in the
 width of the range band corresponds to a relative increase in numbers
          during the corresponding portion of geologic time.]

  PRECAMBRIAN
  PALEOZOIC
    CAMBRIAN
    ORDOVICIAN
    SILURIAN
    DEVONIAN
    MISSISSIPPIAN
    PENNSYLVANIAN
    PERMIAN
  MESOZOIC
    JURASSIC
    CRETACEOUS
  CENOZOIC

  Thallophyta
  Bryophyta
  Tracheophyta
  Protozoa
  Porifera
  Coelenterata
  Bryozoa
  Brachiopada
  Mollusca
  Annelida
  Arthropoda
  Echinodermata
  Chordata

                        [Illustration: Plate 12
                             FOSSIL PLANTS]

                      [Illustration: THALLOPHYTES]

    DIATOMS × 900
    ALGAE × 400

                     [Illustration: TRACHEOPHYTES]

    LEPIDODENDRON × ½
    SIGILLARIA × ½

                        [Illustration: Plate 13
                             FOSSIL PLANTS
                             TRACHEOPHYTES]

    NEUROPTERIS × ½
    PSILOPHYTON × ⅓
    CALAMITES × ½
    AMELANCHIER × ½
    CORDAITES × ¼
    GINGKO × ½

Fairly well-preserved plant remains may also be collected from the
Woodbine group of the Upper Cretaceous in north Texas, and fossil wood,
most of it silicified, has been reported from rocks of almost all ages
and in almost every section of the State. In addition, some of the
carbonaceous clays and shales of east Texas contain large assemblages of
plant leaves, which in some places are well preserved.

It is also possible to find the fossilized remains of seeds, spores, and
pollen. Because of their small size, these minute remains are not
destroyed by the drill bit and can be brought out of deep wells without
being damaged, and for this reason they are a valuable tool for the
micropaleontologist.




                             ANIMAL FOSSILS


The fossilized remains of animals are very common in many of the
sedimentary rocks of Texas. These remains are of many different kinds
and represent the fossils of such diverse organisms as the shell of a
tiny one-celled animal or the bones or tusk of a huge elephant. The
fossils most commonly found, however, are the remains of invertebrate
animals such as clams, snails, and corals, and it is this type of fossil
that attracts the interest of most amateur collectors.

It is not always easy to tell whether certain organisms are plants or
animals, and because of this some scientists have suggested that these
“in-betweens” be placed in a separate kingdom—the Protista. The
protistans are primarily unicellular organisms and are represented by
such forms as bacteria, algae, diatoms, and the protozoans (see below).
But in this publication, only the plant and animal kingdoms are
recognized.


                            Phylum Protozoa

This phylum is composed of simple one-celled animals many of which have
no shell or external body covering. Some, however, have external hard
parts that can become fossilized, and these forms are quite useful
microfossils.

                           CLASS SARCODINA.—

This class contains a group of one-celled animals which may secrete an
exoskeleton (external protective covering) of chitin, silica, or calcium
carbonate. Included in this class are foraminiferans (commonly called
forams) and radiolarians.

                          Order Foraminifera.—

Members of this order secrete tiny chambered shells which are very
useful microfossils. The forams are predominantly marine organisms and
have shells composed of chitin, silica, or calcium carbonate. In
addition, some forms construct a shell of sand grains or some other
material which is cemented together by a sticky substance that is
secreted by the animal.

Forams are very abundant in the rocks of Texas and particularly so in
rocks of Mesozoic and Cenozoic age. The most numerous and easily
observed Paleozoic foraminiferans are the fusulinids (fig. 9a), and
their small spindle-shaped remains are very abundant in many of the
Pennsylvanian limestones of north-central and Trans-Pecos Texas. Some
typical Texas forams are illustrated in figure 9.

                           Order Radiolaria.—

The radiolarians (fig. 10) have delicate spine-covered shells composed
of silica, and their remains are very abundant in certain recent marine
sediments. They may also be found as fossils and have been reported from
Devonian and Permian rocks in Trans-Pecos Texas, and probable
radiolarians have been reported from still younger beds.

     [Illustration: Fig. 9. Typical Texas Foraminifera (all greatly
     enlarged). (a) _Fusulina_ (Pennsylvanian). (b) _Robulus._ (c)
        _Globigerina._ (d) _Frondicularia._ (b-d, Cretaceous).]

  [Illustration: Fig. 10. Typical radiolarians (greatly enlarged). (a)
           _Actinomma_ (Recent). (b) _Porodiscus_ (Eocene).]


                            Phylum Porifera

These are sponges and are the simplest of the many-celled animals.
Living sponges secrete a skeleton which may be composed of chitin,
silica, or calcium carbonate. These substances are commonly found in the
form of spicules—tiny hard parts that are used to help support the soft
tissues of the animal. These spicules take on a variety of shapes (Pl.
14) and are occasionally found as microfossils in some marine sediments.

Although sponges are not particularly common fossils, their remains
occur in some parts of the State. Sponges have been collected from
Paleozoic and Mesozoic formations of north and Trans-Pecos Texas, and
their spicules have been reported from well cuttings.


                          Phylum Coelenterata

The coelenterates are multicelled animals which, though more complex
than the sponges, are rather primitive animals. The living animal is
characterized by a sac-like body cavity, a definite mouth, and tentacles
which bear stinging cells. Some forms, for example, the jellyfishes,
have an umbrella-shaped body and are single free-moving organisms.
Others, like the colonial corals, are composed of many individuals
living together in a colony.

Most zoologists and paleontologists recognize three classes of
coelenterates: (1) the Hydrozoa, containing the small animals known as
hydroids, (2) the Scyphozoa, which includes the jellyfish, and (3) the
Anthozoa, which includes the corals and sea anemones. Because of their
extreme fragility and lack of hard parts, hydrozoans and scyphozoans are
not commonly found as fossils. They do, however, have a long geologic
history and may be preserved when unusual conditions of fossilization
occur. The anthozoans, especially the corals, are by far the most
important class geologically, and these forms have left a very good
paleontological record.

                            CLASS ANTHOZOA.—

This class is composed of a group of exclusively marine organisms and
includes the corals and sea anemones. The coral animal, or _polyp_,
secretes a cup-shaped calcareous (limy) exoskeleton. This skeleton,
called a _corallite_, is usually divided by radial partitions called
_septa_. The polyp lives in the _calyx_, which is the central
bowl-shaped depression in the top of the corallite (fig. 11a).

_Solitary_ corals form an individual corallite for each polyp, and
because of their shape these may be given such names as “horn corals”
(_Lophophyllidium_, Pl. 15) or “button corals” (_Micrabacia_, Pl. 16).
_Colonial_ or _compound_ corals (Pl. 15) live together in colonies,
which are formed of many individual skeletons attached to each other
(fig. 11b), and the compound mass of coral skeletons formed in this
manner is called a _corallum_. Fossil corals commonly occur in many
marine limestones and in places constitute a large portion of the rock.

 [Illustration: Fig. 11. Morphology and principal parts of corals. (a)
       Solitary or “horn” coral. (b) Colonial or compound coral.]

  a
    Columella
    Septum
    Corallite
  b
    Calyx
    Septum
    Corallum

The class Anthozoa has been divided into several subclasses, but only
one, the Zoantharia, is of paleontological importance.

                         Subclass Zoantharia.—

Most corals and all sea anemones belong to this subclass. Zoantharians
are either colonial or solitary and, because most of them possess a hard
preservable exoskeleton, they are the most important group of anthozoans
geologically. The various orders of the subclass Zoantharia are
discussed below.

                             Order Rugosa.—

These are corals in which the septa are arranged in cycles of four. Both
solitary and colonial forms occur, and they are found only in rocks of
Paleozoic age. Rugose corals are abundant in many of the Paleozoic
formations of Texas, and two of the more typical forms
(_Lophophyllidium_ and _Caninia_) are illustrated in Plate 15. Members
of this order have been placed in the subclass Tetracoralla of older
classifications.

                          Order Scleractinia.—

The scleractinians are solitary or colonial corals in which the septa
grow in multiples of six, and they are the most important and abundant
of the modern corals. These corals were the dominant reef builders of
Mesozoic and Cenozoic seas, and their remains are common in many of the
marine formations of the State. Plate 16 illustrates some typical
scleractinian corals from the rocks of Texas. This order has also been
referred to as subclass Hexacoralla, and its members have been called
hexacorals.

                            Order Tabulata.—

These are corals that are now extinct but are known from fossils in both
Paleozoic and Mesozoic rocks. Tabulate corals are characterized by
horizontal partitions called _tabulae_, and septa are absent or poorly
developed. The tabulates were the most abundant reef-building corals
during Paleozoic time and are well known as fossils. Because of certain
similarities with other anthozoans, some paleontologists have treated
the Tabulata as a distinct subclass rather than as an order of the
Zoantharia.

Tabulate corals are not uncommon in many of the Paleozoic rocks of
Texas, and two of these (_Cladochonus_ and _Striatopora_) are
illustrated in Plate 15.


                             Phylum Bryozoa

 [Illustration: Fig. 12. Two types of bryozoans or “moss animals.” (a)
 Section of the lacy type bryozoan. (b) The spiral axis of _Archimedes_
                           (Mississippian).]

Bryozoans are colonial animals that are often referred to as “sea mats.”
They have been called this because they are commonly found matted on
shells, rocks, fossils, and other objects. The living animal is quite
small, has a tentacle-bearing ridge surrounding the mouth, and secretes
a tiny cup-like exoskeleton composed of calcareous or chitinous
material. These little chambers, known as _zooecia_ (or _autopores_),
are seen as small pits on the surface of the bryozoan colony
(_Rhombopora_, Pl. 17). The zooecia grow together to form the bryozoan
colony, and some fossil colonies grow to be as much as 2 feet across.
Such colonies may be spiral (fig. 12b), branching, or lace-like (fig.
12a), and the latter two types are very common in many of the
fossiliferous strata of Texas. Undoubted bryozoan fossils have been
recorded in rocks of Lower Ordovician age, but questionable Cambrian
forms have also been reported. Bryozoans are abundant in the seas of
today, but only a few forms inhabit fresh waters.

                        [Illustration: Plate 14]

                     [Illustration: SPONGE SPICULES
                          (GREATLY ENLARGED)]

                   [Illustration: PALEOZOIC SPONGES]

    MEANDROSTIA × 1
    HELIOSPONGIA × 1
    ASTRAEOSPONGIUM × ½
    ASTYLOSPONGIA × ½
    RECEPTACULITES × ½
    GIRTYOCOELIA × 2

                        [Illustration: Plate 15
                         PENNSYLVANIAN CORALS]

  CLADOCHONUS × 1
  STRIATOPORA × 1
  LOPHOPHYLLIDIUM PROLIFERUM × 1
  MICHELINIA × 1
  CANINIA × 1
  LOPHOPHYLLIDIUM RADICOSUM × 1

                        [Illustration: Plate 16]

                   [Illustration: CRETACEOUS CORALS]

    CLADOPHYLLIA × 1
    PARASMILIA × 1
    PLEUROCORA × 1

                    [Illustration: TERTIARY CORALS]

    ENDOPACHYS × 1
    ASTRHELIA × 1
    FLABELLUM × 1
    MICRABACIA × 2
    TROCHOSMILIA × 1

In Texas one may expect to find bryozoan remains in the Pennsylvanian
rocks of north-central and Trans-Pecos Texas where they are abundant in
certain of the marine shales and limestones. Bryozoans may also be
collected from some Cretaceous and Tertiary beds, but their remains are
small and fragmental and they are easily overlooked. Bryozoans have also
been found matted on the shells of fossil mollusks and other
invertebrates.


                           Phylum Brachiopoda

The brachiopods are a large group of exclusively marine organisms with
shells composed of two pieces called _valves_ (fig. 13). These valves
are usually composed of calcareous or phosphatic material and enclose
and protect the soft parts of the brachiopod animal. The soft parts are
composed of muscles, the _mantle_ (which secretes the valves),
digestive, respiration, reproductive, and excretory organs, and the
tentacle-bearing _lophophore_.

In adult life the brachiopod is attached to the sea bottom by means of a
fleshy stalk called the _pedicle_ (fig. 14), and this is usually
extruded through a hole (the _pedicle foramen_) which is located in the
_ventral_ or _pedicle_ valve. The upturned area which is usually present
on the pedicle valve is called the _beak_. The other valve, known as the
_dorsal_ or _brachial_ valve, is usually the smaller of the two (fig.
13b). The two valves are opened by means of muscles, and since death
results in relaxation of these muscles, fossil brachiopods are typically
found with valves closed.

Brachiopods vary greatly in size and shape and exhibit a wide variety of
ornamentation, such as spines, ribs, nodes, and other structures. They
are abundant fossils in many of the Paleozoic rocks of Texas but are
relatively rare in Mesozoic and Cenozoic formations.

The phylum has been divided into two subclasses, the Inarticulata and
the Articulata. This classification is based upon the nature of the
_hinge-line_—the edge of the shell where the two valves articulate.

  [Illustration: Fig. 13. Morphology and principal parts of articulate
                             brachiopods.]

  a
    Pedicle foramen
    Hinge line
  b
    Pedicle valve
    Beak
    Brachial valve

                          CLASS INARTICULATA.—

The members of this class are rather primitive and have a long geologic
history. These brachiopods have valves which are not provided with hinge
teeth, the valves being held together by muscles, and a hinge-line is
lacking (fig. 14). Most inarticulate brachiopods are circular or
tongue-like in shape and commonly composed of chitinous and phosphatic
material. Inarticulate brachiopods range from Lower Cambrian to Recent
in age but were never as common as the articulate brachiopods, which are
described below. Brachiopods belonging to this class have been recorded
from several Paleozoic formations in Texas (Pl. 17, _Lingula_,
_Apsotreta_, _Angulotreta_).

                        [Illustration: Plate 17]

                [Illustration: PENNSYLVANIAN BRYOZOANS]

    FISTULIPORA × 6
    POLYPORA × 5
    RHOMBOPORA × 8

                  [Illustration: CAMBRIAN BRACHIOPODS]

    APSOTRETA × 10
    LINGULA × 4
    ANGULOTRETA × 10

               [Illustration: MISSISSIPPIAN BRACHIOPODS]

    RHIPODOMELLA × 1
    DICTYOCLOSTUS × 1
    CAMAROTOECHIA × 1

    [Illustration: Fig. 14. _Lingula_, a typical Recent inarticulate
                 brachiopod showing extended pedicle.]

    Pedicle
    Valve

                           CLASS ARTICULATA.—

Articulate brachiopods have a well-defined hinge-line (fig. 13a). One
valve has well-developed teeth which articulate with sockets in the
opposing valve, and there is a well-developed muscle system which aids
in opening and closing the shell. Articulate brachiopods are
characterized by calcareous shells which are typically of unequal size
and a wide variety of shapes (Pls. 18, 19). The class has been divided
into several orders which have been established primarily on the nature
of the pedicle foramen and the nature of shell growth.

Articulate brachiopods range from Lower Cambrian to Recent in age and
are particularly abundant in certain Pennsylvanian formations of
north-central and Trans-Pecos Texas. They are also present in certain
other fossiliferous strata of Paleozoic age but are less abundant and
not as well preserved. The only Cretaceous brachiopod that is found in
large numbers is _Kingena wacoensis_ (Roemer) (fig. 15), which is
particularly abundant in certain formations in the upper part of the
Comanche series.

    [Illustration: Fig. 15. _Kingena wacoensis_, a common Cretaceous
   brachiopod. (a) Dorsal view. (b) Lateral view. (c) Ventral view.]


                            Phylum Mollusca

The phylum Mollusca encompasses a large group of aquatic
(water-dwelling) and terrestrial (land-dwelling) invertebrates which
includes such familiar forms as the snails, clams, oysters, squids, and
octopuses. Most mollusks possess a calcareous shell that serves as an
exoskeleton, and these hard parts are well adapted for preservation as
fossils. However, some mollusks (the slugs) have no shells, and others
(the squids) have an internal calcareous shell. Because of their
relative abundance and great variety, mollusks are particularly useful
fossils. Moreover, the remains of certain mollusks, such as the oysters,
are important rock builders.

The phylum Mollusca has been divided into five classes:

1. _Amphineura_—the chitons or sea-mice; shell composed of eight valves
or plates; not a common fossil. Ordovician to Recent.

2. _Scaphopoda_—the tusk-shells; shell composed of a single tusk-like
valve; generally not a common fossil but locally abundant in certain
Cenozoic formations. Devonian to Recent.

3. _Gastropoda_—the snails and slugs; slugs are without shells, snails
have a single-valved shell which is typically coiled; common fossils in
Paleozoic, Mesozoic, and Cenozoic rocks. Cambrian to Recent.

4. _Pelecypoda_—clams, mussels, oysters, scallops; shells composed of
two valves, usually, but not always, of equal size; common fossils,
especially in Mesozoic and Cenozoic rocks. Cambrian to Recent.

5. _Cephalopoda_—squids, octopuses, the pearly nautilus, and the
ammonoids (extinct); shell of one valve, usually coiled and partitioned
by septa; valuable fossils, especially in Paleozoic and Mesozoic rocks.
?Cambrian, Ordovician to Recent.

                        [Illustration: Plate 18
                       PENNSYLVANIAN BRACHIOPODS]

  MARGINIFERA × 1
  AMBOCOELIA × 1
  SQUAMULARIA × 1
  DERBYA × 1
  MESOLOBUS × 1
  CHONETES × 1
  LINOPRODUCTUS × 1
  PUNCTOSPIRIFER × 1
  COMPOSITA SUBTILITA × 1
  NEOSPIRIFER × 1

                        [Illustration: Plate 19
                       PENNSYLVANIAN BRACHIOPODS]

  JURESANIA × 1
  SPIRIFER ROCKYMONTANUS × 1
  NEOSPIRIFER CAMERATUS × 1

Of these five classes, only the Gastropoda, Pelecypoda, and Cephalopoda
are discussed herein.

                           CLASS GASTROPODA.—

The typical gastropod has a spirally coiled, single-valved, unchambered
shell. This shell encloses a soft body possessing a well-defined head
with a pair of eyes and one or two pairs of tentacles. Most gastropods
have gills and live in shallow marine waters, but some inhabit fresh
water. Others are land-dwelling forms and breathe by means of lungs.

Gastropod shells, both Recent and fossil, exhibit a great variety of
size, shape, and ornamentation. Such shells may be cone-shaped, spirally
coiled, flat, turreted, or cylindrical. The shell is commonly wound in a
spiral around a central axial pillar (the _columella_). The closed
pointed end of the shell is called the _apex_, and each turn of the
shell is called a _whorl_ (fig. 16). The last-formed and largest whorl
is called the _body whorl_, and this whorl contains the _aperture_—the
opening of the shell. The combined whorls exclusive of the body whorl
are known as the _spire_. The inner and outer margins of the aperture
are designated the _inner lip_ and the _outer lip_, respectively. In
some snails the aperture is closed by means of the _operculum_—a
calcareous or horny plate attached to the foot of the animal. This plate
effectively seals the aperture when the animal is withdrawn into its
shell. Some gastropods have shells that are loosely coiled, and in these
forms the columella is absent. If the whorls of such shells are not in
contact on the inner surface, this leaves an open space which is called
the _umbilicus_ (fig. 16a). The umbilicus is commonly seen as an opening
in the base of the gastropod shell, but in some forms the umbilical
opening may be partially or completely covered by a thick growth of
shell called the _callus_.

Many gastropods, particularly those of the Texas Cretaceous, are
commonly preserved as internal or external molds. This type of
preservation occurs after the death of the animal, and the decomposition
of the soft parts enables the shell to become filled with sediment. This
filling later becomes solidified, and the outer shell may eventually be
removed by weathering or solution. This type of internal mold is called
a _steinkern_ and normally does not reflect any external shell
characteristics (Pl. 2). In some of the Pennsylvanian and Tertiary
formations, however, gastropods may be collected with the original shell
in an excellent state of preservation.

Plates 20-23 illustrate some typical Paleozoic, Mesozoic, and Cenozoic
gastropods.

                           CLASS PELECYPODA.—

The pelecypods possess a shell composed of two calcareous valves (fig.
17) which enclose the soft parts of the animal. Members of this class
live exclusively in an aquatic habitat and are most abundant in marine
environments. Most pelecypods are slow-moving bottom-dwelling forms, but
some, like the oysters, are attached. Still others, for example, the
scallop or _Pecten_, are swimmers. The Pelecypoda include such familiar
saltwater forms as the clams and oysters, as well as the common
fresh-water mussel. Pelecypods range from Cambrian to Recent in age but
are more abundant in Mesozoic and Cenozoic rocks.

The living animal is aquatic, with well-developed soft parts and a
muscular, commonly hatchet-shaped _foot_. The soft _mantle_ encloses the
body and secretes the shell, and in some pelecypods part of the mantle
is developed into the _incurrent_ and _excurrent_ siphons. The incurrent
siphons bring fresh water and food into the _mantle cavity_, and waste
products are passed out through the excurrent siphons. Respiration is by
means of gills within the mantle cavity.

The typical pelecypod valves are of equal size and form, but some, such
as the scallops and oysters, have two valves of unequal size and shape.
The valves are hinged and held together by a tough elastic ligament
which runs along the _dorsal_ (top) side of the shell. In addition to
the ligament, most forms have _teeth_ and _sockets_ which are located
along the _hinge-line_. The teeth in one valve articulate with the
sockets in the opposite valve, and this arrangement gives strength to
the hinge.

  [Illustration: Fig. 16. Morphology and principal parts of gastropod
  shells. (a) Low-spired form with umbilicus. (b) Section of spirally
                    coiled shell showing columella.]

  a
    Suture
    Whorl
    Body whorl
    Aperture
    Umbilicus
  b
    Apex
    Spire
    Columella
    Body whorl
    Inner lip
    Outer lip

Most of the pelecypod shell is of calcium carbonate, but the outer
layer, or _periostracum_, of each valve is composed of horny material.
The inner surface of the shell is lined with a calcareous layer of
pearly or porcelaneous material.

                        [Illustration: Plate 20
                       PENNSYLVANIAN GASTROPODS]

  STRAPAROLUS × 1
  AMPHISCAPHA × 1
  WORTHENIA × 1
  TREPOSPIRA × 1
  BELLEROPHON × 1
  EUOMPHALUS × 1

                        [Illustration: Plate 21]

                [Illustration: PENNSYLVANIAN GASTROPODS]

    EUPHEMITES × 1
    STROBEUS × 1
    PLATYCERAS × 1

                  [Illustration: CRETACEOUS GASTROPODS
                            INTERNAL MOLDS]

    GYRODES × 1
    LUNATIA × 1
    TURRITELLA × 1
    CERITHIUM × 1
    TYLOSTOMA × 1
    NERINEA × 1

                        [Illustration: Plate 22
                          TERTIARY GASTROPODS]

  DISTORSIO × 1
  MESALIA × 1
  FUSUS × 1
  COCHLESPIROPSIS × 1
  TURRITELLA × 1
  LATIRUS × 1
  CONUS × 1
  VERTAGUS × 1
  PSEUDOLIVA × 1

                        [Illustration: Plate 23
                          TERTIARY GASTROPODS]

  ANCILLA × 1
  ARCHETECTONICA × 1
  TUBA × 1
  CALYPTRAPHORUS × 1
  SYCOSTOMA × 1
  SURCULA × 1
  VOLUTOLITHES × 1
  NEVERITA × 1
  LEVIFUSUS × 1

The outline of the shell may vary greatly, but most pelecypods are
typically clam-like. However, certain forms are round, others are long
and narrow, and some have wing-like structures. Most pelecypods have a
beak which represents the oldest part of the shell. The _beak_ is
commonly located on the _anterior_ (front) end of the shell, and the end
of the shell opposite this is designated _posterior_ (the rear). The
hinge and ligament are located dorsally (along the top), and the lower
margin of the shell where the valves open is called _ventral_ (fig.
17a).

  [Illustration: Fig. 17. Morphology and principal parts of a typical
        pelecypod shell. (a) Exterior view. (b) Interior view.]

  a
    Dorsal
    Beak
    Anterior
    Posterior
    Concentric growth rings
    Ventral
  b
    Hinge teeth
    Cardinal teeth
    Anterior muscle scar
    Posterior muscle scar
    Mantle line

The inner surface of the shell has certain markings which, along with
the shell form and dentition (the nature and arrangement of the teeth
and sockets), are important in classification. Muscle scars are present
on the inside of most valves; the _anterior muscle scars_ are located
near the front of the shell, and the _posterior muscle scars_ are
situated near the rear of the shell. These scars mark the place of
attachment of muscles which were used to close the shell and aid in
locomotion. Along the ventral margin of some shells there is a line or
scar which extends from the anterior muscle scar to the posterior muscle
scar. This is known as the _mantle line_ or _pallial line_ and marks the
place of attachment of the _mantle_—a soft membranous layer that
enclosed the body of the animal. In some pelecypods the dorsal margin of
one valve bears a series of _hinge teeth_ which articulate with a
similar set of sockets on the other valve (fig. 17b). In addition to
hinge teeth, certain species have _cardinal teeth_ which are located
below and in front of the hinge teeth.

The exterior of most shells is marked by a series of _concentric growth
lines_ (fig. 17a) which mark points of periodic addition of shell
material. The external surface of many shells is also marked by various
types of ornamentation, such as ribs, nodes, spines, and grooves.

Fossil collectors commonly find only one valve of the pelecypod shell.
This is because the shell normally opens when the animal dies, and the
valves may easily become separated. Fossil pelecypods are also commonly
preserved as external and internal molds, and these are found in
fossiliferous strata of almost all ages. Some pelecypods of
Pennsylvanian, Mesozoic, and Cenozoic age are found with original shell
material that appears to have undergone very little change. Fossil
pelecypods are abundant and varied in Texas and are found in most of the
fossiliferous formations of the Pennsylvanian, Cretaceous, and Tertiary
systems (Pls. 24-31).

                          CLASS CEPHALOPODA.—

These are marine mollusks with or without chambered or solid shells
which may be internal or external. The living animal possesses a
well-developed head with eyes, horny jaws, and many tentacles fused with
the foot. Cephalopods are the most advanced of all mollusks and include
the squid, octopus, pearly nautilus, and the extinct ammonoids. Members
of this class range from Cambrian to Recent in age but were much more
abundant in ancient seas than they are today. Their remains constitute a
very useful group of fossils, particularly in Paleozoic and Mesozoic
rocks.

Most paleontologists have divided the Cephalopoda into three subclasses,
the Nautiloidea, Ammonoidea, and the Coleoidea (known also as subclass
Dibranchiata and subclass Decapoda); each of these is discussed below.

                         Subclass Nautiloidea.—

The nautiloids are cephalopods with external chambered shells in which
the _septa_ (dividing partitions) are simple and have smooth edges. This
subclass is represented by a single living genus, _Nautilus_, and a
large number of fossil forms.

In the living _Nautilus_ the shell is composed of calcium carbonate and
is coiled in a flat spiral (fig. 18). The interior of the shell is
divided into a series of _chambers_ by calcareous partitions called
_septa_. The point where each septum joins the inner surface of the
shell is known as the _suture_. These _suture lines_ (fig. 19a) are not
visible from the outside unless the outer shell has been removed, but
they are visible on the internal molds of many fossil cephalopods and
are of great importance in nautiloid and ammonoid classification.
Nautiloids have very simple smoothly curved suture patterns, but
ammonoids are characterized by more complex and wrinkled sutures (fig.
19d).

Although the shell of the only type of living nautiloid is coiled, many
of the early forms had straight cone-shaped shells (_Orthoceras_, Pl.
32), and these are common in some of the Pennsylvanian formations of
Texas. Fossil coiled nautiloids may be collected in certain of the
Cretaceous and Tertiary strata of the State, but their remains are not
common. _Cymatoceras_ (Pl. 32) is a coiled fossil nautiloid from the
Cretaceous of north Texas.

                        [Illustration: Plate 24
                       PENNSYLVANIAN PELECYPODS]

  SCHIZODUS × 1
  MYALINA × ½
  ASTARTELLA × 1
  NUCULOPSIS × 1
  ALLORISMA × 1
  NUCULANA × 1
  YOLDIA × 1
  PINNA × ½

                        [Illustration: Plate 25
                         CRETACEOUS PELECYPODS]

  PROTOCARDIA × 1
  ALECTRYONIA LUGUBRIS × 1
  PLICATULA × 1
  PECTEN × 1

                        [Illustration: Plate 26
                         CRETACEOUS PELECYPODS]

  GRYPHAEA WASHITAENSIS × 1
  GRYPHAEA GRAYSONANA × 1
  INOCERAMUS × 1
  TRIGONIA × 1

                        [Illustration: Plate 27
                         CRETACEOUS PELECYPODS]

  EXOGYRA ARIETINA × 1
  EXOGYRA LAEVISCULA × 1
  NEITHEA × 1
  EXOGYRA PONDEROSA × 1
  EXOGYRA TEXANA × 1

                        [Illustration: Plate 28
                         CRETACEOUS PELECYPODS]

  PACHYMYA × ½
  OSTREA CARINATA × 1
  OSTREA QUADRIPLICATA × 1
  PHOLADOMYA × 1

                        [Illustration: Plate 29
                          TERTIARY PELECYPODS]

  LIMA × 1
  OSTREA LISBONENSIS × 1
  PITAR × 1
  VENERICARDIA BULLA × 1
  PACHECOA × 2
  PHOLADOMYA × 2
  OSTREA SELLAEFORMIS × 1
  CRASSATELLA × 1

                        [Illustration: Plate 30
                          TERTIARY PELECYPODS]

  ORTHOYOLDIA × 1
  TELLINA × 1
  VOKESULA × 2
  NUCULA × 2
  VENERICARDIA × ½

                        [Illustration: Plate 31
                          TERTIARY PELECYPODS]

  PLICATULA × 1
  PECTEN × 1
  ANOMIA × 1
  GLYCYMERIS × 2
  CARYOCORBULA × 2
  BARBATIA × 1

  [Illustration: Fig. 18. Morphology and principal parts of the pearly
nautilus. (a) Exterior view of a Recent shell. (b) Sectioned view of the
                same shell to show internal structures.]

  b
    Living chamber
    Aperture
    Septa
    Siphuncle
    Protoconch
    Chamber

[Illustration: Fig. 19. Characteristic features of the various types of
    cephalopod sutures. (a) Nautiloid type. (b) Goniatite type. (c)
                   Ceratite type. (d) Ammonite type.]

                         Subclass Ammonoidea.—

The ammonoids are a group of extinct cephalopods which are related to
the nautiloids but are characterized by more complex suture patterns.
Members of this subclass have an external partitioned shell which is
straight, curved, or spirally coiled (Pl. 33). This group of cephalopods
first appeared in Devonian time, became extremely abundant and varied
during the Mesozoic, and was extinct by the end of the Cretaceous
period.

Most Paleozoic ammonoids are characterized by a combination curved and
angular suture pattern, and this type of suture pattern is referred to
as _goniatitic_ (fig. 19b). Sutures that are curved and crenulated
(marked in places by a series of tooth-like indentations) are known as
_ceratitic_ (fig. 19c). Ceratitic sutures first appeared in the
Mississippian, became increasingly abundant during the Triassic but were
much less abundant during the Cretaceous. The _ammonitic_ suture has a
very complexly subdivided pattern (fig. 19d). Cephalopods with ammonitic
sutures range from Pennsylvanian to Cretaceous in age and were the most
abundant cephalopods of the Mesozoic.

                        [Illustration: Plate 32]

               [Illustration: PENNSYLVANIAN CEPHALOPODS]

    PHANEROCERAS × 1
    ORTHOCERAS × 1

                 [Illustration: CRETACEOUS CEPHALOPODS]

    METOICOCERAS × ½
    CYMATOCERAS × ½

                        [Illustration: Plate 33
                        CRETACEOUS CEPHALOPODS]

  TEXANITES × ½
  ACANTHOCERAS × ½
  TURRILITES × ½
  DUFRENOYIA × ½
  OXYTROPIDOCERAS × ½
  BACULITES × ½
  BELEMNITE × ½

Ammonoids are locally abundant in many of the fossiliferous rocks of
Texas and are among the more useful Mesozoic guide fossils. Goniatites
may be found in the Pennsylvanian of north-central and Trans-Pecos
Texas, and ammonoids with the ceratitic suture pattern can be collected
from the Lower Cretaceous of many parts of the State. Cephalopods
exhibiting the typical ammonitic suture pattern are abundant in many of
the Cretaceous rocks of Texas, and these fossils have contributed much
toward an understanding of the Cretaceous strata of this State.

                          Subclass Coleoidea.—

These are squid-like cephalopods characterized by an internal shell or
no shell at all. Included in this group are the squids, cuttlefish,
octopuses, and the extinct belemnoids, but of these only the belemnoids
are useful fossils. Members of this subclass range from Mississippian to
Recent in age.

                          Order Belemnoidea.—

The belemnoids appear to be the oldest and most primitive of the coleoid
cephalopods. Their earliest known occurrence is in rocks of
Mississippian age, and they were particularly abundant during the
Mesozoic. They became extinct at the end of Cretaceous time but have
left considerable evidence of their existence in the Mesozoic strata of
many parts of the world. Certain forms, because of their abundance and
relatively short geologic range, are excellent guide fossils. Belemnoids
have been found in the Upper Cretaceous of Texas (Pl. 33) but in general
are rare or unknown in most Texas formations.


                            Phylum Annelida

Members of the phylum Annelida include the segmented worms such as the
common earthworm. Annelids are marine, fresh water, or terrestrial and
have apparently been common through much of geologic time. Because of
their lack of hard parts, most of these worms have left little direct
fossil evidence of their activities in the geologic past. Some annelids
secrete straight or coiled calcareous tubes, and fossil worm tubes of
this sort (fig. 20) are commonly found attached to brachiopods,
mollusks, and other objects. Tubes of this nature have been reported
from Paleozoic, Mesozoic, and Cenozoic rocks in Texas.

 [Illustration: Fig. 20. Types of typical annelid worms. (a) _Serpula_
            (×1) (b) _Hamulus_ (×2). (c) _Spirobis_ (×15).]

Some annelids have small chitinous jaws and teeth which also may be
preserved as fossils. These dental structures are called scolecodonts
and are microfossils.


                           Phylum Arthropoda

The arthropods are one of the more advanced groups of invertebrates, and
they are known from the Cambrian to the Recent (Pl. 34). Modern
representatives of this group include the crabs, shrimp, crayfish,
insects, and spiders. Arthropods vary greatly in size and shape and are
among the most abundant of all animals. They have become successfully
adapted to a wide variety of environments and live on land, in water,
and in the air. The typical arthropod has a segmented body which is
usually covered by a chitinous exoskeleton which, in some forms,
contains additions of calcium carbonate. They are highly specialized and
well-developed animals in which locomotion is by means of paired jointed
appendages.

Although the arthropods are of great importance in nature today, only a
few groups are of importance to the paleontologist. Only two of these,
the trilobites and the ostracodes, are discussed herein.


                       Subphylum Trilobitomorpha

The members of this subphylum are extinct arthropods which were most
abundant during early Paleozoic time.

                           CLASS TRILOBITA.—

The trilobites are a group of exclusively marine arthropods which derive
their name from the typical three-lobed appearance of their bodies (fig.
21a). The trilobite body is divided into a _central_ or _axial_ lobe and
two _lateral_ lobes. The body of the animal was encased in a chitinous
exoskeleton. The top part of this exterior covering, the _carapace_, is
very thick, and it is this part of the trilobite that is usually
preserved.

                        [Illustration: Plate 34
                           FOSSIL ARTHROPODS]

  FOSSIL INSECT × 1
  FOSSIL CRUSTACEANS
    ENOPLOCLYTIA × 1⅓
    ASTACODES × ¾
    NOTOPOCORYSTES × 2
    OSTRACODES × 40

 [Illustration: Fig. 21. Morphology and principal parts of trilobites.]

  Cephalon
  Thorax
  Pygidium
  Axial lobe
  Lateral lobes

The body is also divided into three parts from front to back. Beginning
at the front of the animal these divisions are the _cephalon_ or head,
the _thorax_ or abdomen, and the _pygidium_ or tail (fig. 21a). The body
segments of the thorax were arranged in such a manner as to permit the
animal to roll up into a ball, and many trilobites are found in this
position (fig. 21b).

Trilobites first appeared in the Cambrian and were extinct by the end of
the Permian. They occur sparingly in certain of the Paleozoic rocks of
Texas and when found are likely to be fragmental and in a poor state of
preservation.


                          Subphylum Crustacea

The crustaceans are the crabs, shrimp, crayfish, and ostracodes.
Although not abundant, fossil crabs have been described from certain
Cretaceous and Tertiary formations of the State (_Notopocorystes_, Pl.
34). However, the most useful and abundant crustacean fossils are the
members of the class Ostracoda.

                           CLASS OSTRACODA.—

The ostracodes are small, bivalved, aquatic crustaceans which have the
external appearance of small clams (Pl. 34). The remains of these tiny
animals are so small that they are best studied under a low-power
microscope, and because of their small size they are particularly useful
to the micropaleontologist.

Fossil ostracodes range from Ordovician to Recent in age and have been
recorded in the Paleozoic, Mesozoic, and Cenozoic rocks of Texas. Their
remains are particularly abundant in certain of the Cretaceous and
Tertiary marine formations of the State.


                          Phylum Echinodermata

The echinoderms are a large group of exclusively marine animals, most of
which exhibit a marked five-fold radial symmetry (Pls. 35, 36). Living
echinoderms have well-developed nervous and digestive systems, a
distinct body cavity, and are a relatively complex group of organisms.

The typical echinoderm has a skeleton composed of numerous calcareous
plates which are intricately fitted together and covered by a leathery
outer skin (the _integument_). The echinoderm body often exhibits a
typical star-shaped form, but some types may be heart-shaped,
biscuit-shaped, or cucumber-shaped.

Members of this phylum range from Cambrian to Recent in age and are
abundant as fossils in many of the marine formations of Texas.

The phylum Echinodermata has been divided into two subphyla, the
Pelmatozoa (those forms that were attached to sea floor by a stem or a
stalk) and the Eleutherozoa (the stemless unattached echinoderms).


                          Subphylum Pelmatozoa

These are echinoderms which are more or less permanently attached to the
bottom of the sea by means of a stalk which is composed of slightly
movable, calcareous, disk-like segments (fig. 23).

Pelmatozoans range from Cambrian to Recent in age, and their fossilized
remains are particularly abundant in Paleozoic rocks. The subphylum has
been divided into several classes, but only three of these, the
Cystoidea, Blastoidea, and Crinoidea, are discussed here. With the
exception of the Crinoidea, all of the attached echinoderms are extinct.

                           CLASS CYSTOIDEA.—

These are primitive attached echinoderms which were relatively common in
early Paleozoic time. The typical cystoid has a somewhat globular or
sac-like _calyx_ (the main body skeleton) composed of numerous,
irregularly arranged, calcareous plates (fig. 22b). The plates composing
the calyx are usually perforated by pores or slits which were probably
used in excretion or respiration. The calyx was attached to the sea
bottom by a short stem.

Cystoids range from Cambrian to Devonian in age and were especially
abundant during Ordovician and Silurian time. Their remains are rare or
absent in the rocks of Texas.

     [Illustration: Fig. 22. Two extinct attached echinoderms. (a)
    _Pentremites_ (Mississippian). (b) _Caryocrinites_ (Silurian).]

                           CLASS BLASTOIDEA.—

The blastoids are extinct short-stemmed echinoderms with a small,
symmetrical, bud-like calyx. The blastoid calyx is composed of 13
calcareous plates arranged in a typical five-sided pattern (fig. 22a).
The _mouth_ is located in the center of the calyx and is surrounded by
five openings called _spiracles_. Five distinct _ambulacral_ or _food
grooves_ radiate outward from the mouth.

Blastoids range from Ordovician to Permian in age and were especially
abundant during the Mississippian period. No blastoids have been
reported from any of the rocks of Texas.

                           CLASS CRINOIDEA.—

The crinoids are commonly called _sea-lilies_ because of their
flower-like appearance. The _calyx_ is composed of symmetrically
arranged calcareous plates, and most crinoids have a long stem. Other
crinoids are free-swimming in the adult stage and are attached only
during the earlier phases of their development.

The crinoid calyx is typically cup-shaped (fig. 23) and five grooves
radiate out from its center. These grooves continue outward along the
complexly segmented arms and are used as channels to convey food to the
mouth.

 [Illustration: Fig. 23. Typical modern crinoid, or “sea lily,” showing
                           principal parts.]

  Calyx
    Arm
    Plate
  Stem
    Columnal
    Cirri
  Holdfast (root)

The crinoid stem is attached to the base of the calyx and serves for
purposes of support and attachment. This stem consists of a relatively
long flexible stalk composed of numerous calcareous disk-shaped segments
called _columnals_ (fig. 23; Pl. 35), each of which contains a round or
star-shaped opening in its center. Many crinoids have very long stalks
(some are as much as 50 feet in length), and when the animal dies the
columnals become separated and are scattered about on the ocean floor.
Many Paleozoic limestones contain such great numbers of crinoid
columnals that they are referred to as _crinoidal limestones_ (fig. 8).
Crinoidal limestones occur in some of the Mississippian and
Pennsylvanian formations of central Texas and in the Pennsylvanian of
north-central and Trans-Pecos Texas.

The stalk is attached to the sea floor or some other object by means of
a root system called the _holdfast_ (fig. 23). This structure commonly
branches out into the surrounding sediments, and in this manner the
crinoid animal is firmly anchored to the bottom of the sea.

Crinoids, like most echinoderms, are gregarious animals—that is, they
commonly live together in large numbers, and for this reason great
numbers of crinoid remains are commonly found concentrated in relatively
small local areas. Most fossil crinoids are found as stem fragments
because the more fragile calyx and root system are less likely to be
preserved.

The earliest known crinoids have been found in rocks of Ordovician age,
and their remains are particularly abundant in Paleozoic rocks. Crinoids
are living today but most of them are stemless free-swimming forms
called “feather stars,” much less abundant than their Paleozoic
ancestors.


                         Subphylum Eleutherozoa

The eleutherozoans are free-swimming, bottom-dwelling, echinoderms which
have been divided into two classes. The class Asterozoa (star-shaped
echinoderms) contains the subclasses Asteroidea (the starfishes) and the
Ophiuroidea (the brittle stars). Although they are known as fossils,
neither of these groups is of paleontological importance. The class
Echinozoa (echinoderms without laterally directed arm-like extensions)
contains the subclasses Echinoidea (the sea urchins and sand dollars)
and Holothuroidea (the sea cucumbers). Of these two subclasses, only the
Echinoidea are useful fossils.

                           CLASS ASTEROZOA.—

These are typical star-shaped free-moving echinoderms in which the body
is divided into a central disk and radiating arms.

                         Subclass Asteroidea.—

This class contains the starfishes which, although not common fossils,
illustrate well the typical echinoderm characteristics (Pl. 35). Fossil
starfishes have been found sparingly in certain formations in Texas, but
well-preserved specimens are quite rare. However, excellently preserved
starfishes have been found in slabs of Cretaceous limestones from
central and north-central Texas.

                         Subclass Ophiuroidea.—

The ophiuroids are echinoderms with a well-defined central disk and five
long, slender, whip-like arms. They have been called brittle stars
because of their ability to shed their arms when they are disturbed.
Their long, slender, snake-like arms have also resulted in their being
called serpent stars. Ophiuroids range from Ordovician to Recent in age,
but because of the delicate nature of their bodies they are seldom found
as fossils. Ophiuroid remains have been found in certain Mesozoic and
Cenozoic rocks of Texas, but they consist largely of small segments of
the arms or body fragments.

                           CLASS ECHINOZOA.—

The echinozoans are a group of unattached echinoderms whose bodies
consist of numerous calcareous plates and spines, but they do not
possess the radiating arm-like extensions which characterize the
asterozoans.

                         Subclass Echinoidea.—

Echinoids are free-moving echinoderms with disk-shaped, heart-shaped,
biscuit-shaped, or globular exoskeletons (Pl. 36). Modern
representatives of this group include the familiar sea urchins, heart
urchins, and the sand dollars.

                        [Illustration: Plate 35]

  CRINOIDS
    CRINOID CALYX × ½
    CRINOID COLUMNALS × 1
  HOLOTHURIAN SCLERITES (GREATLY ENLARGED)
  CRETACEOUS FOSSIL STARFISHES
    PENTAGONASTER × 1
    PENTACEROS × 1

                        [Illustration: Plate 36
                         CRETACEOUS ECHINOIDS]

  SALENIA × 1
  ECHINOID SPINES × 2
  ECHINOID PLATE × 2
  HEMIASTER × 1
  HOLASTER × 1
  HOLECTYPUS × 1

The echinoid _test_ (exoskeleton) is composed of many intricately
fitting calcareous plates (Pl. 36) which enclose the animal’s soft
parts. The exterior of the test is typically covered with large numbers
of movable spines (Pl. 36) which vary greatly in size. These spines are
of some aid in locomotion, support the skeleton of the animal, and
provide a measure of protection from enemies.

The oldest known echinoids have been recorded from rocks of Ordovician
age, but it was not until the Mesozoic that the group began to flourish.
They were especially abundant during the Cretaceous and have been
abundant and varied from that time until the present.

Echinoids are particularly numerous in many of the Lower Cretaceous
formations of Texas where they are commonly found in an excellent state
of preservation. Heart urchins and biscuit urchins may be found in large
numbers in many areas of the State, and especially in areas where there
are good exposures of fossiliferous Lower Cretaceous rocks.

                        Subclass Holothuroidea.—

Members of this class, commonly called _sea cucumbers_, have a rather
elongate, sac-like, cucumber-shaped body and bear little resemblance to
other members of the phylum Echinodermata. The sea cucumbers do not have
a well-defined skeleton; rather the body is supported by many small,
disconnected, calcareous plates or rods called _ossicles_ or _sclerites_
(Pl. 35). These minute structures are embedded in the leathery skin
which covers the body of the sea cucumber and may be preserved as
fossils. Such remains are locally abundant in certain formations in
Texas, but because of their small size, scattered occurrence, and
problems in classification, this group is of little use to most
paleontologists.

Holothuroid body impressions have been reported from the Middle
Cambrian, and sclerites from rocks as old as Mississippian.


                            Phylum Chordata

The chordates are the most advanced of all animals and are characterized
by the presence of a well-developed nervous system and a body supported
by a bony or cartilaginous _notochord_ and/or _spinal column_. In the
higher chordates (the vertebrates) the notochord is normally replaced by
bone, but in the lower chordates (for example, the graptolites) it
remains in a cartilaginous condition.

The phylum Chordata contains only two subphyla of paleontological
significance. These are the subphylum Hemichordata, composed of
primitive chordates (including the graptolites which are important
fossils), and the Vertebrata, which includes all animals with backbones.


                         Subphylum Hemichordata

The hemichordates are characterized by a well-defined notochord which
runs the length of the body, but they do not possess a true backbone.
Only one class, the Graptolithina, is of paleontological importance.

                         CLASS GRAPTOLITHINA.—

The graptolites are a group of extinct colonial animals which were very
abundant during early Paleozoic time. They are characterized by a
chitinous exoskeleton consisting of rows of cups or tubes which housed
the living animal. These cups are attached to single or branching stalks
(fig. 24) which in some forms were attached to sea weeds, rocks, or
other foreign objects where they led a fixed existence. The stalks of
the unattached graptolites grew on floats (fig. 24a) and these floating
forms attained wide geographic distribution. It is also possible that
some of the attached forms were fixed to floating objects, such as sea
weed, and thus were distributed in this manner.

Previous classifications have recognized the graptolites as members of
the phylum Coelenterata. As coelenterates they were assigned, at various
times, to the classes Hydrozoa, Scyphozoa, and Graptozoa. In addition,
they were also classified as bryozoans by certain of the early
paleontologists. This publication, in keeping with recent changes in
taxonomy, considers graptolites to be an extinct group of hemichordates.
This classification is based upon research in which uncompressed
graptolites were etched out of chert and studied in great detail.
Information derived from these relatively undistorted specimens
indicates a much higher degree of body organization than was previously
suspected, and as a result of these studies most paleontologists now
consider graptolites to be some form of primitive chordate.

    [Illustration: Fig. 24. Graptolites. (a) Diplograptus (×2). (b)
              Dendrograptus (×3). (c) Phyllograptus (×2).]

The chitinous graptolite exoskeleton is commonly preserved as a
flattened carbon residue; their remains may be locally abundant along
the bedding planes of certain black or dark gray shales.

Graptolites are known from rocks that range from Cambrian to
Mississippian in age, and they are among the most important guide
fossils for Ordovician and Silurian rocks.

Graptolites have been reported from Cambrian rocks in central Texas and
from the Ordovician of west Texas (fig. 24). The most abundant of these
occur in certain Ordovician rocks in the Trans-Pecos area where they are
common fossils in certain formations.


                          Subphylum Vertebrata

The vertebrates are the most advanced of all chordates. They are
characterized by a skull and a bony or cartilaginous _internal
skeleton_, with a _vertebral column_ of bone or cartilage. This
subphylum is commonly divided into two superclasses, the Pisces (the
fishes and their relatives) and the Tetrapoda (the four-footed animals).

As mentioned earlier, most amateur collectors collect very few
vertebrate remains, and for this reason this group is not discussed in
detail. However, the more important vertebrate classes are briefly
reviewed to enable the reader to have some understanding of this
important group of animals. This part of the handbook will also serve as
an introduction to some of the interesting and unusual, but now extinct,
animals that have inhabited Texas in the geologic past. Among these
animals are giant fishes, primitive amphibians, and many different types
of dinosaurs. Included also are such unusual mammals as the giant ground
sloths, saber-tooth cats, mammoths, and mastodons, all of which are now
extinct. The remains of these, and many other interesting extinct
vertebrates, may be seen in the geological collections of the Texas
Memorial Museum at Austin. Many of these displays are accompanied by
drawings which depict the scientific restoration of the animal’s soft
parts and show how the animal may have appeared in life.

                           Superclass Pisces

The members of this superclass are commonly called fishes and are the
simplest and most numerous of all vertebrates. They are aquatic,
free-moving, cold-blooded (their blood maintains the temperature of the
surrounding water), and breathe primarily by means of gills. However,
some forms (the lungfishes) breathe by means of a lung developed from
the air-bladder.

The most recent fish classification recognizes four major classes, the
Agnatha (primitive jawless fishes), the Placodermi (armored fishes with
primitive jaws), the Chondrichthyes (sharks and related forms with
cartilaginous internal skeletons), and the Osteichthyes (true bony
fishes).

                            CLASS AGNATHA.—

Fishes belonging to this class are primitive, jawless, and represented
by the living lampreys and hagfishes. The first agnathans appeared in
the Ordovician and were armored by a bony covering on the front part of
their bodies. These primitive fishes, called _ostracoderms_, are the
earliest recorded fishes and, in addition, appear to be the first known
vertebrate animals. The ostracoderms first appeared in late Ordovician
time, increased in numbers in the Silurian, and were extinct by the end
of the Devonian.

                           CLASS PLACODERMI.—

These are primitive jaw-bearing fishes, the majority of which were
heavily armored (Pl. 37). The _placoderms_ were shark-like in
appearance, and some of them grew to be as much as 30 feet in length.
Members of this class appeared first in the Devonian and lasted into the
Permian, at which time they became extinct. Placoderms are rare in
Texas, but the fragmentary remains of these primitive fishes have been
found in Devonian rocks in central Texas.

                         CLASS CHONDRICHTHYES.—

This class includes such modern forms as the sharks, rays, and skates.
They are characterized by skeletons which are composed of cartilage and
are very abundant in the marine waters of today. The earliest known
representatives of this class are reported from rocks of Devonian age,
and they have been relatively common up to the present time.

Shark teeth (Pl. 37) can be found in Texas in Pennsylvanian, Permian,
Cretaceous, Paleocene, Eocene, and Miocene rocks. These are probably the
most common vertebrate fossils to be found in Texas and are usually
found in thin-bedded marine limestones or clays.

                          CLASS OSTEICHTHYES.—

The Osteichthyes includes the true bony fishes, which are the most
highly developed and abundant of all fishes. They possess an internal
bony skeleton, well-developed jaws, an air-bladder, and, typically, an
external covering of overlapping scales.

Included in this class are a primitive group of fishes called
_crossopterygians_. These were very abundant in the Devonian and are
believed to be the ancestors of the amphibians. The modern lungfishes
also belong to the class Osteichthyes, and these primitive fishes, which
are now found only in Australia, South America, and Africa, breathe by
means of gills and lungs which have been developed from the air-bladder.
Although not abundant as fossils, the remains of these specialized
fishes have added much to present knowledge concerning the development
of certain of the higher vertebrates.

The remains of bony fishes have been collected at many localities in
Texas, and fossils of this type have been found primarily in rocks of
Cretaceous age but have been reported from other rocks as well. Fish
fossils are more commonly found in the form of teeth (Pl. 37),
vertebrae, scales, and an occasional well-preserved skeleton.

                        [Illustration: Plate 37]

                    [Illustration: SHARK TEETH × 1]

                        [Illustration: CONODONTS
                          (GREATLY ENLARGED)]

                 [Illustration: PRIMITIVE ARMORED FISH
                          PLACODERM (DEVONIAN)
                                  × ½]

_Conodonts_ (Pl. 37) are small, amber-colored, tooth-like fossils which
are believed to represent the teeth of some type of extinct fish.
Although geologists do not know a great deal about the origin of these
strange fossils they are of value in micropaleontology. Conodonts have
been reported from several Paleozoic formations in Texas and are useful
guide fossils in some areas.

                          Superclass Tetrapoda

The tetrapods are the most advanced chordates and are typified by the
presence of lungs, a three- or four-chambered heart, and paired
appendages. Included here are the classes Amphibia (frogs, toads, and
salamanders), Reptilia (lizards, snakes, turtles, and the extinct
dinosaurs), Aves (birds), and Mammalia (including the mammals, such as
men, dogs, whales, etc.).

                            CLASS AMPHIBIA.—

The amphibians were the earliest developed four-legged animals and are
represented by such living forms as the toads, frogs, and salamanders.
Amphibians are cold-blooded animals that primarily breathe by lungs and
spend most of their life on land, but during their early stages of
development they live in the water where they breathe by means of gills.

The amphibians apparently developed from the crossopterygian fishes
during late Devonian time and were relatively abundant in the
Pennsylvanian, Permian, and Triassic.

Amphibian remains in Texas are confined largely to lower Paleozoic and
upper Mesozoic rocks. Numerous interesting and important discoveries of
fossil amphibians have been made in north and west Texas where their
remains (Pl. 40) have been collected in association with early types of
reptiles. The areas where Permian red beds are exposed in Archer and
Baylor counties and where Triassic red beds are exposed from Big Spring
north along the edge of the High Plains have furnished most of these
specimens.

                            CLASS REPTILIA.—

The reptiles have become adapted to permanent life on land and need not
rely on an aquatic environment. They are cold-blooded and are normally
characterized by a scaly skin. Reptiles have been much more abundant in
the past than they are today, and they assumed many different shapes and
sizes in the geologic past. Modern classifications recognize a large
number of reptilian groups, but only the more important of these are
briefly reviewed here.

                             Cotylosaurs.—

These were a group of primitive reptiles which, although retaining some
amphibian characteristics, became adapted to an exclusively
land-dwelling existence. The cotylosaurs lived during the Pennsylvanian
and Permian and apparently became extinct sometime during the late
Permian. Cotylosaurs (Pl. 40) are well known from the Permian of north
Texas.

                               Turtles.—

These are reptiles in which the body is more or less completely enclosed
by bony plates. This group is first known as fossils from late Triassic
rocks of Europe, and modern representatives of the group include the
turtles and tortoises. Fragmentary remains of turtle shells are among
the most common vertebrate fossils found in the Tertiary. Some of the
late Tertiary land tortoises were 3 to 4 feet long. The earliest known
turtles in Texas have been found in Cretaceous rocks.

                             Pelycosaurs.—

The pelycosaurs were a group of late Paleozoic reptiles some of which
were characterized by the presence of a tall fin on their back (Pl. 40).
The fossils of these unusual creatures are well known from the Permian
red beds of north-central Texas.

                              Therapsids.—

The therapsids were a mammal-like group of reptiles which were well
developed for a terrestrial existence. Although the remains of these
primitive reptiles are not particularly important fossils, study of the
therapsids has provided much valuable information about the origin of
the mammals. Members of this group appeared first in the middle Permian
and persisted until the middle Jurassic, but therapsid remains have not
been reported from Texas.

                        [Illustration: Plate 38
  Comparison of the dinosaurs. Reproduced with permission of Dr. J. W.
  Dixon, Jr., and Geology Department, Baylor University, Waco, Texas.]

    DINOSAUR               SAURISCHIANS                                          ORNITHISCHIANS
     STOCKS

  DINOSAUR      THEROPOD           SAUROPOD         ORNITHOPOD        STEGOSAUR       CERATOPSIAN      ANKYLOSAUR
  TYPES
  POSTURE       BIPEDAL            QUADRUPEDAL      BIPEDAL AND       QUADRUPEDAL     QUADRUPEDAL      QUADRUPEDAL
                                                    QUADRUPEDAL
  ARMOR         UNARMORED EXCEPT   UNARMORED        UNARMORED (SPEED  BONY PLATES     HORNS, BONY      KNOBS AND SPIKES
                FOR HUGE SHARP                      WAS CHIEF         ALONG BACK,     PLATE OVER NECK  OVER DORSAL AREA,
                TEETH                               DEFENSE)          SPIKED-TAIL                      CLUB-LIKE TAIL
  DIET          CARNIVOROUS        HERBIVOROUS      HERBIVOROUS       HERBIVOROUS     HERBIVOROUS      HERBIVOROUS
  OTHER         LARGE HEAD WITH    HUGE BODY, LONG  SLENDER-BUILD,    SHORT NECK,     SHORT NECK,      “ARMADILLO-LIKE”
  DESCRIPTIVE   POWERFUL JAW,      NECK AND TAIL,   “DUCK-BILLED”     LONG TAIL,      STOCKY BUILD     APPEARANCE
  REMARKS       GREATLY REDUCED    SMALL HEAD                         SMALL HEAD
                FORE-LIMBS
  EXAMPLES      CERATOSAURUS-J     BRACHIOSAURUS-J  PARASAUROLOPHUS-K _STEGOSAURUS-J_ STYRACOSAURUS-K  PALEOSCINCUS-K
  (AND AGE)     ALLOSAURUS-J       DIPLODOCUS-J     CORYTHOSAURUS-K                   PROTOCERATOPS-K  _ANKYLOSAURUS-K_
  J-JURASSIC    _TYRANNOSAURUS-K_  _BRONTOSAURUS-J_ _TRACHODON-K_                     _TRICERATOPS-K_
  K-CRETACEOUS
                [Illustration]     [Illustration]   [Illustration]    [Illustration]  [Illustration]   [Illustration]
  SCALE IN FEET 10                 10               5                 5               5                5

                        [Illustration: Plate 39
  Comparison of Mesozoic flying and swimming reptiles. Reproduced with
   permission of Dr. J. W. Dixon, Jr., and Geology Department, Baylor
                       University, Waco, Texas.]

               [Illustration: FLYING REPTILES—PTEROSAURS]

        GROUP          AGE         TEETH        TAIL       HEAD        SIZE           EXAMPLE

  RHAMPHORHYNCHOIDS JURASSIC   WELL          LONG TAIL  WITHOUT     SMALL      [Illustration]
                               DEVELOPED     WITH       CREST       MAXIMUM    _RHAMPHORHYNCHUS_
                                             FLATTENED              WINGSPAN
                                             RUDDER AT              OF 2 FEET
                                             END
  PTERODACTYLOIDS   JURASSIC   JAW PARTLY    SHORT OR   WITH SMALL  FROM SIZE  [Illustration]
                    AND        OR            NO TAIL    OR LARGE    OF         _PTERANODON-K_
                    CRETACEOUS COMPLETELY               CREST       SPARROW
                               TOOTHLESS,                           TO GIANTS
                               HORNEY BEAK                          WITH SPAN
                                                                    OF 25′

               [Illustration: MESOZOIC SWIMMING REPTILES]

      GROUP         AGE        DESCRIPTION       SIZE      HABITAT        EXAMPLE

  ICHTHYOSAUR    TRIASSIC   FISH-LIKE BODY,   AVERAGE    MARINE      [Illustration]
                 TO         HEAD LONG AND     LENGTH =               _ICHTHYOSAURUS-J_
                 CRETACEOUS POINTED, NO       7′
                            DISTINCT NECK     MAXIMUM
                                              LENGTH =
                                              43′
  MOSASAUR       CRETACEOUS LIZARD-LIKE       AVERAGE    MARINE      [Illustration]
                            BODY, FLATTENED   LENGTH =               _PYLOSAURUS_
                            TAIL,             15′-20′
                            DOUBLE-JOINTED    MAXIMUM
                            JAW, RECURVED     LENGTH =
                            TEETH             50′
  PLESIOSAUR     TRIASSIC   LONG NECK AND     MAXIMUM    MARINE      [Illustration]
                 TO         SMALL HEAD OR     LENGTH =               _ELASMOSAURUS-K_
                 CRETACEOUS LONG HEAD AND     50′                    _TRINACROMERUM-K_
                            SHORT NECK,
                            POWERFUL FLIPPERS
  CHELONIA       TRIASSIC   SHAPED LIKE       MAXIMUM    MARINE,     [Illustration]
  (TURTLES)      TO PRESENT MODERN TURTLES,   SIZE =     STREAMS,    _ARCHELON-K_
                            BODY COVERED      11′ × 12′  AND
                            WITH BONY PLATES             TERRESTRIAL
  PHYTOSAUR      TRIASSIC   CROCODILE-LIKE    MAXIMUM    STREAMS     [Illustration]
                            BODY, NOSTRILS    LENGTH =   AND SWAMPS  _RUTIODON_
                            ON A “HUMP”       25′
                            ALMOST BETWEEN
                            THE EYES

                        [Illustration: Plate 40]

  PELYCOSAUR × ¹/₁₂
    DIMETRODON
  PRIMITIVE AMPHIBIAN × ¹/₂₀
    ERYOPS
  COTYLOSAUR
    SEYMOURIA × ⅕

                        [Illustration: Plate 41
                           SWIMMING REPTILES]

  ICHTHYOSAUR × ¹/₁₂₀
  MOSASAUR × ¹/₆₀
  PLESIOSAUR × ¹/₆₀

                        [Illustration: Plate 42]

                 [Illustration: CROCODILE-LIKE REPTILE
                                 × ¹/₅₀
                               PHYTOSAUR]

                    [Illustration: FLYING DINOSAURS]

    RHAMPHORHYNCHUS × ⅙
    PTERANODON × ¹/₄₀

                             Ichthyosaurs.—

These were extinct, short-necked, marine reptiles that were fish-like in
appearance. Ichthyosaurs resemble the modern dolphins, and some of them
attained lengths of 25 to 40 feet (Pl. 41), though the average was much
less. The group is known from rocks ranging from middle Triassic to late
Cretaceous in age.

                              Mosasaurs.—

The mosasaurs are another group of extinct marine lizards which lived in
Cretaceous seas. Some of these great reptiles grew to be as much as 50
feet long, and their great gaping jaws were filled with many sharp
recurved teeth (Pl. 41). Mosasaurs were present in the great Cretaceous
seas which covered many parts of Texas, and their remains have been
reported from both north and central Texas. One such skeleton was found
near Austin, and its skull is on display in the Texas Memorial Museum.

                             Plesiosaurs.—

The plesiosaurs were marine reptiles which were characterized by a broad
turtle-like body, paddle-like flippers, and a long neck and tail (Pl.
41). These reptiles were not as streamlined or well equipped for
swimming as the ichthyosaurs or mosasaurs, but the long serpent-like
neck was probably very useful in helping the reptile catch fish and
other small animals for food. Plesiosaur remains range from middle
Triassic to late Cretaceous in age, and they have been found in
Cretaceous rocks in Texas. A short-necked plesiosaur which was collected
from Upper Cretaceous rocks near Waco is on display in the Strecker
Museum at Baylor University in Waco.

                              Phytosaurs.—

The phytosaurs were a group of crocodile-like reptiles which ranged from
6 to 25 feet in length (Pl. 42). They resembled the crocodiles both in
appearance and in their mode of life, but this similarity is only
superficial, and the phytosaurs and crocodiles are two distinct groups
of reptiles.

The phytosaurs are exclusively Triassic in age and their remains have
been collected from Triassic rocks along the eastern margin of the High
Plains of Texas.

                      Crocodiles and alligators.—

These reptiles adapted themselves to the same type habitat that was
occupied by the phytosaurs, which preceded them. Crocodiles and
alligators were much larger and more abundant during Cretaceous and
Cenozoic time than they are today; the crocodiles first appeared in the
Cretaceous and the alligators in the Tertiary. The remains of both
crocodiles and alligators have been found in Texas, and one such
crocodile (_Phobosuchus_) represents the remains of the largest
crocodile yet discovered (Pl. 43). This specimen probably had an overall
length of 40 to 50 feet, and its massive skull was 6 feet long and
possessed exceptionally strong jaws. The remains of this great beast
were collected from exposures of Upper Cretaceous rocks along the Rio
Grande in Trans-Pecos Texas.

                              Pterosaurs.—

These were Mesozoic reptiles with bat-like wings supported by arms and
long thin “fingers” (Pl. 42). The pterosaurs were well adapted to life
in the air, and their light-weight bodies and wide skin-covered wings
enabled them to soar or glide for great distances. The earliest known
pterosaurs were found in lower Triassic rocks, and the group became
extinct by the end of the Cretaceous. During this time certain of these
creatures attained a wingspread of as much as 27 feet, but their bodies
were small and light.

                              Dinosaurs.—

The collective term “dinosaurs” (meaning terrible lizards) has been
given to that distinctive group of reptiles prominent in Mesozoic life
for some 140 million years. In size, the dinosaurs ranged from as little
as 1 foot to as much as 85 feet in length and from a few pounds to
perhaps 45 tons in weight. Some were _carnivorous_ (meat-eaters) but the
majority were _herbivorous_ (plant-eaters). Some were _bipedal_ (walked
on their hind-legs) while others were _quadrupedal_ (walked on all
fours), and although most of the dinosaurs were terrestrial in habitat,
aquatic and semi-aquatic forms were also present.

According to the structure of their hip bones, the dinosaurs have been
divided into two great orders. These are the Saurischia (forms with
lizard-like pelvic girdle) and the Ornithischia (dinosaurs with a
bird-like pelvic girdle).

                        [Illustration: Plate 43
       Dr. Brown, R. T. Bird, and Dr. Schaikjer with the skull of
 _Phobosuchus_, an extinct crocodile from the Cretaceous of Trans-Pecos
                                 Texas.
    Photograph courtesy of the American Museum of Natural History.]

                           Order Saurischia.—

Dinosaurs belonging to this order were particularly abundant during the
Jurassic and are characterized by hip bones that are similar to those of
modern lizards. These dinosaurs were first discovered in rocks of
Triassic age and did not become extinct until the end of the Cretaceous.
The lizard-hipped reptiles are divided into two rather specialized
groups of dinosaurs: the _theropods_ (carnivorous bipedal dinosaurs that
varied greatly in size) and the _sauropods_ (herbivorous, quadrupedal,
semi-aquatic, usually gigantic dinosaurs).

                          SUBORDER THEROPODA.—

This type of saurischian dinosaur walked on bird-like hind limbs, and
they were exclusively meat-eating forms, such as _Allosaurus_ (Pl. 44)
of Jurassic age. Some theropods were exceptionally large and were
undoubtedly vicious beasts of prey. This assumption is borne out by such
anatomical features as the small front limbs with long sharp claws for
holding and tearing flesh, and the large strong jaws which were armed
with numerous, sharp, dagger-like teeth. The largest of all known
theropods was _Tyrannosaurus rex_ which, when standing on his hind
limbs, was almost 20 feet tall. Some individuals were as much as 50 feet
long, and _Tyrannosaurus_ is believed to have been among the most
vicious animals to ever inhabit our earth. A cast of the skull of one of
these great beasts is on display in the Texas Memorial Museum at Austin,
and a _Tyrannosaurus_ tooth has been found in the Big Bend National Park
in Trans-Pecos Texas.

                          SUBORDER SAUROPODA.—

The sauropods were the largest of all dinosaurs, and some attained a
length of 85 feet and probably weighed 40 to 50 tons (_Brontosaurus_,
Pl. 44). They were primarily herbivorous dinosaurs which had become
adapted to an aquatic or semi-aquatic type of existence and probably
inhabited lakes, rivers, and swamps. The tracks of sauropod dinosaurs
have been collected from Lower Cretaceous rocks in central Texas (Pl. 4)
and Upper Cretaceous beds in Big Bend National Park in Trans-Pecos
Texas.

                          Order Ornithischia.—

The ornithischian, or bird-hipped dinosaurs, were herbivorous reptiles
which were quite varied in form and size and appear to have been more
highly developed than the saurischians. This order includes the
duck-billed dinosaurs (ornithopods), the plate-bearing dinosaurs
(stegosaurs), the armored dinosaurs (ankylosaurs), and the horned
dinosaurs (ceratopsians). Ornithischian tracks are known from Cretaceous
rocks in central and Trans-Pecos Texas.

                         SUBORDER ORNITHOPODA.—

These unusual dinosaurs were predominantly bipedal, semi-aquatic, and
some (like the duck-billed dinosaurs) were highly specialized
(_Trachodon_, Pl. 45).

                         SUBORDER STEGOSAURIA.—

The stegosaurs were herbivorous, quadrupedal ornithischians with large
projecting plates down the back and heavy spikes on their tails. The
Jurassic dinosaur _Stegosaurus_ (Pl. 45) is most typical of the
plate-bearing forms. This creature weighed about 10 tons, was some 30
feet long, and stood about 10 feet tall at the hips. _Stegosaurus_ is
characterized by a double row of large, heavy, pointed plates which run
along the animal’s back. These plates begin at the back of the skull and
stop near the end of the tail. The tail was also equipped with four or
more long curved spikes which were probably used as a means of defense.
The animal had a very small skull which housed a brain that was about
the size of a walnut, and it is assumed that these, and all other
dinosaurs, were of very limited intelligence.

_Stegosaurus_ remains have not been discovered in Texas, but these, like
certain other of the extinct vertebrates, are mentioned because of their
interesting and unusual form.

                        SUBORDER ANKYLOSAURIA.—

The ankylosaurs were four-footed, herbivorous, Cretaceous dinosaurs
which had relatively flat bodies. The skull and back of the animal were
protected by bony armor, and the club-like tail was armed with spikes.
_Paleoscincus_ (Pl. 45), a typical ankylosaur, had large spines
projecting from along the sides of the body and tail. The armored spiked
back and the heavy club-like tail probably provided _Paleoscincus_ with
much-needed protection from the vicious meat-eating dinosaurs of
Cretaceous time.

                        [Illustration: Plate 44
                         SAURISCHIAN DINOSAURS]

  ALLOSAURUS × ¹/₁₈₀
  BRONTOSAURUS × ¹/₂₅₀

                        [Illustration: Plate 45
                        ORNITHISCHIAN DINOSAURS]

  STEGOSAURUS × ¹/₉₀
  TRACHODON × ¹/₁₀₀
  PALEOSCINCUS × ¹/₂₅
  TRICERATOPS × ¹/₁₂₀

                         SUBORDER CERATOPSIA.—

The ceratopsians, or horned dinosaurs, are another group of dinosaurs
that are known only from rocks of Cretaceous age. These plant-eating
dinosaurs possessed beak-like jaws, a bony neck frill which extended
back from the skull, and one or more horns. _Triceratops_ (Pl. 45) is
the largest of the horned dinosaurs (some forms were as much as 30 feet
long), and the skull measured 8 feet from the tip of the parrot-like
beak to the back of the neck shield.

                              CLASS AVES.—

Because of the fragile nature of their bodies, birds are seldom found as
fossils. In spite of this, however, some interesting and important
fossil bird remains have been discovered.

The oldest known bird was found in Upper Jurassic rocks exposed in
Germany. This primitive bird, named _Archaeopteryx_, is little more than
a reptile with feathers. _Archaeopteryx_ was a pigeon-sized creature
which had scales as well as feathers, a lizard-like tail, a toothed
beak, and other definitely reptilian characteristics.

During late Cretaceous time the birds underwent changes that resulted in
forms similar to those that are living today, and most of the
present-day birds had developed by the end of the Tertiary.

Although not commonly found, fossil birds have been recorded from
certain of the Cenozoic rocks of Texas.

                            CLASS MAMMALIA.—

The mammals are animals that are born alive and fed with milk from the
mother’s breast. They are warm-blooded, air-breathing, have a protective
covering of hair, and are the most advanced of all vertebrates. The
foregoing features are the more typical mammalian characteristics, but
exceptions to these are found in certain mammals.

Mammals first appeared in the Jurassic and were probably derived from
some form of mammal-like reptile. Although rare during the Mesozoic,
mammals underwent rapid development and expansion during the Cenozoic,
and during this era certain types of mammals became extremely large and
assumed many bizarre shapes. The majority of these unusual forms lived
but a short time but are well known from their fossils, and the remains
of some of these animals which inhabited Texas during the Cenozoic may
be seen in the Texas Memorial Museum at Austin.

Recent mammalian classification recognizes several subclasses and
numerous orders and suborders, but the treatment of the mammals in a
publication of this nature must of necessity be somewhat brief and no
attempt at detailed classification is made.

                         Subclass Allotheria.—

The allotherians first appeared during the Jurassic and underwent
considerable development in the late Cretaceous and early Tertiary.
Included in this subclass are the _multituberculates_ which are a group
of small rodent-like animals that were probably the earliest of the
herbivorous mammals. These animals were probably never very numerous,
and they became extinct during the early part of Eocene time.

                           Subclass Theria.—

Members of this subclass are first known from rocks of Jurassic age, and
they constitute the largest group of mammals that are living today.
Therians undergo considerable development before they are born and at
birth typically resemble the fully developed animal. This subclass has
been divided into several orders but only the more important ones are
discussed here.

                            Order Edentata.—

The edentates are a rather primitive group of mammals which are
represented by such living forms as the anteaters, tree sloths, and
armadillos. Members of this group were common in the southern part of
the United States in Pleistocene and Pliocene time, and fossil edentates
have been reported from rocks of this age in Texas. One such form was
_Mylodon_ (Pl. 46), one of the extinct giant ground sloths. These huge
sloths were quite heavy and some of them stood as much as 15 feet tall;
these great creatures were the forerunners of the modern tree sloths of
South America. The mounted skeleton of one of these giant ground sloths
is displayed in the Texas Memorial Museum.

                        [Illustration: Plate 46
                           CENOZOIC MAMMALS]

  ENTELODONT × ¹/₃₅
  GLYPTODON × ¹/₅₀
  MYLODON × ¹/₉₀

Another interesting representative of this order was the glyptodont.
These peculiar mammals, which were ancestral to the present-day
armadillos, developed at about the same time as the ground sloths.
_Glyptodon_ (Pl. 46), a typical glyptodont that has been reported from
the Pleistocene of Texas, is quite characteristic of this group. This
armadillo-like beast had a solid turtle-like shell that in some forms
was as much as 4 feet high. From the front of the bone capped head to
the tip of its tail, a large individual might be as much as 15 feet
long. The thick heavy tail was protected by a series of bony rings, and
in some species the end of the tail was developed into a bony heavily
spiked club. The _carapace_ (hard outer shell) of a large glyptodont is
mounted at the Texas Memorial Museum.

                           Order Carnivora.—

Animals belonging to this order are called carnivores and are
characterized by clawed feet and by teeth which are adapted for tearing
and cutting flesh. The carnivores, or meat-eaters, were first
represented by an ancient group of animals called _creodonts_, and this
short-lived group first appeared in the Paleocene and were extinct by
the end of the Eocene. They ranged from the size of a weazel to that of
a large bear, and their claws were sharp and well developed. Their
teeth, however, were not as specialized as those of modern carnivores,
and the creodont brain was relatively small. It is assumed that these
animals had a very low order of intelligence when compared to the more
advanced carnivores of today.

These early meat-eaters were followed by more specialized carnivores
which developed throughout Cenozoic time. Some examples of these are the
saber-tooth cat _Dinobastis_ (Pl. 47) and the dire wolf _Canis diris_
(Pl. 47), both of which have been reported from the Texas Pleistocene.
Some remains of these unusual forms, representing the cat and dog
families, are on display at the Texas Memorial Museum.

                           Order Pantodonta.—

Pantodonts, known also as _amblypods_, were primitive, hoofed,
herbivorous animals. They were distinguished by a heavy skeleton, short
stout limbs, and blunt spreading feet. The pantodonts appeared first
during Paleocene time and had become extinct by the end of the
Oligocene.

                           Order Dinocerata.—

The members of this order are an extinct group of gigantic mammals
commonly called _uintatheres_. _Uintatherium_ (Pl. 48), which is typical
of the group, had three pairs of blunt horns, and the males had
dagger-like upper tusks. Some of the uintatheres were as large as a
small elephant and stood as much as 7 feet tall at the shoulders. The
size of the brain in relation to the size of the body suggests that
these animals were not as intelligent as most mammals. Uintatheres are
known from rocks ranging from Paleocene to Eocene in age. Uintathere
remains have been reported from Big Bend National Park in Trans-Pecos
Texas.

                          Order Proboscidea.—

The earliest proboscideans, the elephants and their relatives, first
appeared in the late Eocene of Africa and were about the size of a small
modern elephant but had larger heads and shorter trunks. Proboscidean
development is marked by an increase in size, change in skull and tooth
structure, and elongation of the trunk. Two well-known fossil
proboscideans are the _mammoth_ and the _mastodon_, both of which
inhabited Texas during Pleistocene time. The mastodons resembled the
elephants, but the structure of their teeth was quite different (fig.
25). Moreover, the mastodon skull was lower than that of the elephant
and the tusks were exceptionally large—some reaching a length of 9 feet.

                        [Illustration: Plate 47
                           CENOZOIC MAMMALS]

  DINOBASTIS × ¹/₂₀
  CANIS DIRUS × ¹/₁₅
  HYRACOTHERIUM × ¹/₁₀
  PLIOHIPPUS × ¹/₂₀

There were several types of mammoths, and the _woolly mammoth_ is
probably the best known. This animal lived until the end of the
Pleistocene and, like the woolly rhinoceros discussed below, is known
from ancient cave paintings and frozen remains. Information gathered
from these sources indicates that this great beast had a long coat of
black hair with a woolly undercoat (Pl. 49).

[Illustration: Fig. 25. Sketches of Pleistocene (a) mastodon tooth (×⅙)
                      and (b) mammoth tooth (×⅙).]

During the Pleistocene, mammoths were widespread over the United States,
and their remains are abundant in many stream deposits of this age.
Proboscidean bones have been reported from Pleistocene rocks in many
parts of Texas, where they are commonly found in sand and gravel pits.

                         Order Perissodactyla.—

The perissodactyls, or odd-toed animals, are mammals in which the
central toe on each limb is greatly enlarged. Modern representatives
include the horses, rhinoceroses, and tapirs. Extinct members of the
Perissodactyla include the _titanotheres_, _chalicotheres_, and
_baluchitheres_, all of which grew to tremendous size and took on many
unusual body forms.

                                HORSES.—

One of the first perissodactyls was _Hyracotherium_ (also called
_Eohippus_), which is the earliest known horse (Pl. 47). This small
animal, whose remains have been found in Big Bend National Park, was
about 1 foot high and his teeth indicate a diet of soft food. Following
the first horse, there is a long series of fossil horses which provide
much valuable information on the history of this important group of
animals.

The record of the development of the horse is well represented in Texas,
and the bones and teeth of fossil horses are common in certain parts of
the State. Fossils of this type have been reported from the Tertiary of
the Trans-Pecos, Gulf Coastal Plain, and High Plains regions of Texas,
and the teeth of Pleistocene horses have been found in sand and gravel
pits in many parts of the State. Horse teeth (fig. 26) are particularly
useful fossils as they may be accurately identified and used to
determine the age of the rocks in which they are found.

 [Illustration: Fig. 26. Typical Pliocene horse tooth. Top view (a) and
                 lateral view (b) of molar tooth (×½).]

                             TITANOTHERES.—

This group of odd-toed mammals appeared first in the Eocene, at which
time they were about the size of a sheep. By Middle Oligocene time they
had increased to gigantic proportions but still had a small and
primitive brain. _Brontotherium_ (Pl. 48) was slightly rhinoceros-like
in appearance and is believed to be the largest land animal that ever
inhabited the North American continent. This animal was about 8 feet
tall at the shoulders; a large bony growth protruded from the skull and
this was extended into a flattened horn, which was divided at the top.

                        [Illustration: Plate 48
                           TERTIARY MAMMALS]

  UINTATHERIUM × ¹/₄₅
  BRONTOTHERIUM × ¹/₃₅

Although the titanotheres underwent rapid development during the early
Tertiary, these huge beasts became extinct during the middle of the
Oligocene epoch. Titanothere remains have been reported from the
Trans-Pecos region of Texas.

                            CHALICOTHERES.—

The chalicotheres were in some ways like the titanotheres, but they also
exhibited many peculiarities of their own. The head and neck of
_Moropus_, a typical chalicothere, were much like that of a horse, but
the front legs were longer than the hind legs, and the feet resembled
those of a rhinoceros except that they bore long claws instead of hoofs.
The chalicotheres lived in North America from Miocene until Pleistocene
time but were probably never very numerous, and their remains have not
yet been discovered in Texas.

                             RHINOCEROSES.—

The rhinoceroses are also odd-toed animals, and there are many
interesting and well-known fossils in this group. The _woolly
rhinoceros_ (Pl. 49) was a Pleistocene two-horned form that ranged from
southern France to northeastern Siberia. The woolly rhinoceros is well
known from complete carcasses recovered from the frozen tundra of
Siberia and from remains that were found preserved in an oil seep in
Poland. These unusual specimens plus cave paintings made by early man
have given a complete and accurate record of this creature. Although the
woolly rhinoceros has not been reported from Texas, other fossil
rhinoceroses have been found in the High Plains and Gulf Coastal Plain
of Texas. These fossils have been found in rocks ranging from Middle
Oligocene to late Pliocene in age.

_Baluchitherium_, the largest land mammal known to science, was a
hornless rhinoceros that lived in late Oligocene and early Miocene time.
This immense creature measured approximately 25 feet from head to tail,
stood almost 18 feet high at the shoulder, and must have weighed many
tons. Remains of these creatures have not been discovered in North
America, and they appear to have been restricted to Central Asia.

                          Order Artiodactyla.—

The artiodactyls are the even-toed hoofed mammals and include such
familiar forms as pigs, camels, deer, goats, sheep, and hippopotamuses.
This is a large and varied group of animals, but the basic anatomical
structure of the limbs and teeth show well the relationship between the
different forms. Artiodactyls are abundant fossils in rocks ranging from
Eocene to Pleistocene in age and are common in rocks of this age in
Texas.

                             ENTELODONTS.—

These giant pig-like artiodactyls lived during Oligocene and early
Miocene time and were distinguished by a long heavy skull that held a
relatively small brain. The face was marked by large knobs which were
located beneath the eyes and on the underside of the lower jaw, and
although these knob-like structures were blunt they had the appearance
of short horns. Certain of these giant swine attained a height of 6 feet
at the shoulders and had skulls that measured 3 feet in length (Pl. 46).
Entelodont remains have been found in the Miocene of the Texas Coastal
Plain.

                                CAMELS.—

The first known camels have been reported from rocks of upper Eocene
age, and these small forms underwent considerable specialization of
teeth and limbs as they developed in size. Many of the camels that lived
during the middle Cenozoic had long legs which were well adapted to
running and long necks which would have allowed the animals to browse on
the leaves of tall trees.

The earliest known Texas camels were found in rocks of Oligocene age,
and camels, like horses, must have been abundant in Texas during the
Pleistocene for their fossilized remains are common in many parts of the
State.

                        [Illustration: Plate 49
                           CENOZOIC MAMMALS]

  WOOLLY RHINOCEROS × ¹/₂₀
  WOOLLY MAMMOTH × ¹/₄₀




                          BOOKS ABOUT FOSSILS


The following books are recommended for the reader who wants to know
more about fossils and fossil collecting. The publications listed below
cover various phases of historical geology and paleontology and range
from children’s books to the more technical publications of the
professional paleontologist. This list, however, is by no means
all-inclusive and many other interesting and useful publications are
available.


                             GENERAL WORKS


Dunbar, C. O. (1959) Historical geology, John Wiley and Sons, New York.

  College-level text, well written and well illustrated.


Moore, R. C. (1958) Introduction to historical geology, McGraw-Hill Book
Co., New York.

  College-level presentation of earth history. Many illustrations of
  fossils.


Moore, Ruth (1953) Man, time, and fossils, Alfred Knopf, New York.

  A readable account of fossils and their development throughout
  geologic time.


Panghorn, M. W., Jr. (1957) Earth for the layman, American Geological
Institute, Washington, D. C.

  Contains many valuable references.


Raymond, P. E. (1950) Prehistoric life, Harvard University Press,
Cambridge, Mass.

  College-level text.


Richards, H. G. (1953) Record of the rocks, Ronald Press, New York.

  College-level earth history text.


Simpson, G. G. (1953) Life of the past, Yale University Press, New
Haven, Conn.

  Thorough, yet readable, introduction to paleontology.


Stirton, R. A. (1959) Time, life, and man: the fossil record, John Wiley
and Sons, New York.

  An introductory college text, most of which is of interest to adult
  level general readers.


Note: _See also_ sections on Paleontology and Fossils _in_ Encyclopedia
Americana, Encyclopaedia Britannica, and others.


                       NONTECHNICAL AND JUVENILE


Andrews, R. C. (1953) All about dinosaurs, Random House, New York.

  Interesting and readable dinosaur book for junior high and high-school
  age.


Andrews, R. C. (1956) All about strange beasts of the past, Random
House, New York.

  Interesting and easy to read, this book deals largely with extinct and
  unusual mammals (junior high and high school).


Colbert, E. H. (1945) The dinosaur book, American Museum of Natural
History, New York.

  A classic among “popular” dinosaur books. For all age levels.


Colbert, E. H. (1957) Dinosaurs, American Museum of Natural History, New
York.

  This little booklet provides a well-illustrated introduction to the
  dinosaurs. For high school and adult-level readers.


Dickinson, Alice (1954) First book of prehistoric animals, Franklin
Watts, Inc., New York.

  Easy to read, well-illustrated book for grade-school age.


Dunkle, D. H. (1957) The world of the dinosaurs, Smithsonian
Institution, Washington, D. C.

  An easy to understand, amply illustrated introduction to the dinosaurs
  (high school-adult level).


Fenton, C. L. (1937) Life long ago, The John Day Co., New York.

  Very good for advanced grade and high-school age.


Heal, Edith (1930) How the world began, Thomas S. Rockwell Co., Chicago.

  An account of the beginnings of life. For upper grade through
  high-school age.


Markman, H. C. (1954) Fossils, Denver Museum of Natural History, Denver,
Colo.

  A well-illustrated general survey of fossils. For adult-level readers.


Matthews III, W. H. (1962) Fossils: An introduction to prehistoric life,
Barnes and Noble, Inc., New York, [“In preparation” at time of first
printing of Guidebook No. 2.]

  This publication contains many collecting aids and much background
  material for amateur collectors. Contains also a brief review of earth
  history.


Matthews III, W. H. (1963) Wonders of the dinosaur world, Dodd, Mead &
Co., New York.

  Well illustrated, non-technical presentation of dinosaurs. For
  junior-high and high-school teachers.


Parker, B. M. (1942) Stories read from the rocks, Basic Science
Education Series, Row, Peterson and Co., Evanston, Ill.

  Well written and colorfully illustrated. For advanced grades and
  junior high.


Parker, B. M. (1948) Animals of yesterday, Basic Science Education
Series, Row, Peterson, and Co., Evanston, Ill.

  Well written and colorfully illustrated. For advanced grades and
  junior high.


Shaver, R. H. (1959) Adventures with fossils, Geological Survey, Indiana
Department of Conservation, Bloomington, Ind.

  Collection hints and general information on fossils. Particularly for
  the lower grades.


Shuttlesworth, D. E. (1957) Real book of prehistoric life, Garden City
Books, Garden City, N. Y.

  Survey of prehistoric life. For grade and junior-high levels.


                               COLLECTING HELPS


Brown, Vinson (1954) How to make a home nature museum, Little, Brown and
Co., Boston.

  Contains suggestions for collecting, mounting, and displaying fossils
  and other objects of nature.


Camp, C. L., and Hanna, G. D. (1937) Methods in paleontology, University
of California Press, Berkeley.

  Excellent discussion of collecting and preparation techniques.


Casanova, Richard (1957) An illustrated guide to fossil collecting,
Natureograph Co., San Martin, Calif.

  Has collecting hints and fossil localities for most of the States.


Collinson, C. C. (1959) Guide for beginning fossil hunters, Educational
Series 4, Illinois State Geological Survey, Urbana.

  Clearly written, well illustrated, particularly for the lower grades.


Goldring, Winifred (1950) Handbook of paleontology for beginners and
amateurs, New York State Museum, Albany, N. Y.

  A complete summary of paleontology. For the advanced collector.


La Rocque, A., and Marple, M. F. (1955) Ohio fossils, Ohio Division of
Geological Survey, Bulletin 54, Columbus, Ohio.

  Rather comprehensive treatment of the invertebrates with several
  useful keys for fossil identification.


Livingston, V. E., Jr. (1959) Fossils in Washington, Division of Mines
and Geology, Department of Conservation, Olympia, Wash.

  An introduction to the geology and fossils of Washington. Contains
  guide to collecting localities.


Simpson, B. W. (1958) Gem trails of Texas, Bessie W. Simpson, Granbury,
Texas.

  Field guide to Texas mineral, rock, and fossil locations. Contains
  numerous maps and well-described collecting localities.


Unklesbay, A. G. (1955) Common fossils of Missouri, University of
Missouri Bulletin, Handbook 4, Columbia, Mo.

  Written for the amateur; contains much general information of interest
  to the beginning collector.


                               REFERENCE WORKS


Arnold, C. A. (1947) An introduction to paleobotany, McGraw-Hill Book
Co., New York.

  College-level textbook.


Beerbower, J. R. (1960) Search for the past, Prentice-Hall, Inc.,
Englewood Cliffs, N. J.

  Good background text. Well illustrated. Has section on vertebrates.


Colbert, E. H. (1955) Evolution of the vertebrates, John Wiley and Sons,
New York.

  Comprehensive and technical treatment of vertebrate fossils.


Cushman, J. A. (1948) Foraminifera, their classification and economic
use, Harvard University Press, Cambridge, Mass.

  College-level text containing large numbers of descriptions and
  illustrations of foraminifera.


Easton, W. H. (1960) Invertebrate paleontology, Harper & Bros., Inc.,
New York.

  College-level text. Good illustrations, useful for identification.


Fenton, C. L., and Fenton, M. A. (1958) The fossil book, Doubleday and
Co., New York.

  Comprehensive, easy-to-read, beautifully illustrated treatment of all
  types of fossils.


Jones, D. J. (1956) Introduction to microfossils, Harper and Brothers,
New York.

  College-level textbook with considerable information on collection,
  preparation, and the types of microfossils.


Moore, R. C., et al. (1953-1959) Treatise on invertebrate paleontology,
Geological Society of America and University of Kansas, Lawrence,
Kansas.

  A technical reference for the more advanced collector. It is issued in
  several parts and contains latest classification.


Moore, R. C., Lalicker, C. G., and Fisher, A. G. (1953) Invertebrate
fossils, McGraw-Hill Book Co., New York.

  College-level reference with fine illustrations. Of value for purposes
  of identification.


Romer, A. S. (1945) Vertebrate paleontology, University of Chicago
Press, Chicago.

  A college-level textbook with numerous illustrations.


Shimer, H. W. (1933) Introduction to the study of fossils, The Macmillan
Company, New York.

  A relatively simple college-level presentation of plant and animal
  fossils.


Shimer, H. W., and Shrock, R. R. (1944) Index fossils of North America,
John Wiley and Sons, New York.

  Comprehensive survey of the more common fossils of North America.
  Useful to the advanced collector and a most useful aid for fossil
  identification.


Shrock, R. R., and Twenhofel, W. H. (1953) Principles of invertebrate
paleontology, McGraw-Hill Book Co., New York.

  Useful college-level reference for advanced collectors.


                   SELECTED REFERENCES ON TEXAS FOSSILS[2]


*Adkins, W. S. (1920) The Weno and Pawpaw formations of the Texas
Comanchean: Univ. Texas Bull. 1856.

  Descriptions and illustrations of many common Cretaceous fossils.


*Adkins, W. S. (1928) Handbook of Texas Cretaceous fossils: Univ. Texas
Bull. 2838.

  Lists all fossils described from the Texas Cretaceous prior to 1928,
  with many useful illustrations.


*Adkins, W. S., and Winton, W. M. (1919) Paleontological correlation of
the Fredericksburg and Washita formations of north-central Texas: Univ.
Texas Bull. 1945.

  Contains descriptions and illustrations of many common Lower
  Cretaceous fossils of north-central Texas.


Clarke, W. B., and Twitchell, M. W. (1915) The Mesozoic and Cenozoic
Echinodermata of the United States: U. S. Geological Survey Monograph
54, Washington, D. C.

  A valuable guide to the Mesozoic and Cenozoic echinoderms of Texas.


*Frizzell, D. L. (1954) Handbook of Cretaceous Foraminifera of Texas:
Univ. Texas, Bureau Econ. Geol. Rept. Inves. No. 22.

  A technical, but invaluable aid in the study of Texas Cretaceous
  microfossils.


*Girard, R. M. (1959) Bibliography and index of Texas geology,
1933-1950: Univ. Texas Pub. 5910.

  This valuable reference guide contains many references to Texas
  fossils. Note especially entries under Paleontology in the index.


Heuer, Edward (1958) Comments on the nomenclature revision of the Strawn
and Canyon megafossil plates, _in_ A guide to the Strawn and Canyon
Series of the Pennsylvanian System in Palo Pinto County, Texas, An
Occasional Publication of the North Texas Geological Society, Wichita
Falls, Texas.

  Contains illustrations and latest name changes of many of the more
  common Pennsylvanian fossils of north Texas.


*King, R. E. (1930) Geology of the Glass Mountains, Part II, Faunal
summary and correlation of the Permian formations with description of
Brachiopoda: Univ. Texas Bull. 3042.

  Contains descriptions and illustrations of numerous brachiopods from
  the Glass Mountains of Trans-Pecos Texas.


*Lee, Wallace, et al. (1939) Stratigraphic and paleontologic studies of
the Pennsylvanian and Permian rocks of north-central Texas: Univ. Texas
Pub. 3801.

  Contains an extensive faunal list and important collecting localities
  for Pennsylvanian invertebrates.


*Moore, R. C., and Jeffords, R. M. (1944) Description of lower
Pennsylvanian corals from Texas and adjacent states: Univ. Texas Pub.
4401, pp. 77-208.

  Describes and illustrates many of the more common Pennsylvanian
  corals.


*Plummer, F. B. (1943) The Carboniferous rocks of the Llano region of
central Texas: Univ. Texas Pub. 4329.

  Contains geologic map, locality data, and illustrations of many
  Carboniferous fossils.


*Plummer, F. B., and Moore, R. C. (1921) Stratigraphy of the
Pennsylvanian formations of north-central Texas: Univ. Texas Bull. 2132.

  Describes and illustrates many of the more common Pennsylvanian
  fossils of north-central Texas.


*Plummer, F. B., and Scott, Gayle (1937) Upper Paleozoic ammonites in
Texas: Univ. Texas Bull. 3701, pt. 1.

  *Renick, B. C., and Stenzel, H. B. (1931) The lower Claiborne of the
  Brazos River, Texas: Univ. Texas Bull. 3101, pp. 73-108.


Contains discussion and illustrations of many common Tertiary fossils.

  Sellards, E. H. (1955) Texas through 250 million years: Museum Notes
  No. 4, Texas Memorial Museum, Austin.


This little booklet provides a short geologic history of Texas along
with a review of oil in Texas.

  *Sellards, E. H., Adkins, W. S., and Plummer, F. B. (1933) The geology
  of Texas, Vol. I, Stratigraphy: Univ. Texas Bull. 3232 (August 22,
  1932).


This important publication will give the advanced collector much
valuable information on the distribution of the rocks of Texas. Complete
with geologic map.

  Stanton, T. W. (1947) Studies of some Comanche pelecypods and
  gastropods: U. S. Geological Survey Prof. Paper 211, Washington, D. C.


Describes and illustrates most of the more common Lower Cretaceous
pelecypods and gastropods of the State.

  *Stenzel, H. B., Krause, E. K., and Twining, J. T. (1957) Pelecypoda
  from the type locality of the Stone City beds (Eocene) of Texas: Univ.
  Texas Pub. 5704.


Descriptions and illustrations of many of the more common Tertiary clams
and oysters.

  *Stephenson, L. W. (1941) The larger invertebrate fossils of the
  Navarro group of Texas: Univ. Texas Pub. 4101.


Contains descriptions of many common Upper Cretaceous invertebrates
(exclusive of corals and crustaceans).

  Stephenson, L. W. (1952) Larger invertebrate fossils of the Woodbine
  formation (Cenomanian) of Texas: U. S. Geological Survey Prof. Paper
  242, Washington, D. C.


*Winton, W. M. (1925) The geology of Denton County: Univ. Texas Bull.
2544.

  Illustrates and discusses the occurrence of many Cretaceous fossils.


*Winton, W. M., and Adkins, W. S. (1920) The geology of Tarrant County:
Univ. Texas Bull. 1931.

  Contains many illustrations of common north Texas Cretaceous fossils.




                                GLOSSARY


Amber—a hard, yellowish, translucent, fossilized plant resin.

Ammonite—ammonoid cephalopod with complexly wrinkled suture pattern;
  member of subclass Ammonoidea.

Anterior—front or fore.

Anus—the terminal opening of the alimentary canal, through which waste
  matter is discarded from the body.

Aperture—the opening of shells, cells, etc.

Aragonite—calcium carbonate (CaCO₃) crystallizing in a different form
  than calcite. In shells it is chalky and opaque; is less stable than
  calcite.

Archeozoic—the oldest known geological era; early Precambrian time.

Articulated—joined by interlocking processes or by teeth and sockets.

Asymmetrical—without or lacking symmetry.

Bilateral—pertaining to the two halves of a body as symmetrical and
  mirror images of each other.

Binomial nomenclature—system of scientific nomenclature requiring two
  names: generic and trivial.

Blastoid—stalked echinoderm with bud-like calyx usually consisting of 13
  plates; member of class Blastoidea.

Brachiopod—bivalved marine invertebrate; member of phylum Brachiopoda.

Brackish—a mixture of salt and fresh waters.

Burrow—a hole in the ground, rock, wood, etc., made by certain animals
  for shelter or while gathering food.

Calcareous—composed of, or containing, calcium carbonate; limy.

Calcite—calcium carbonate (CaCO₃) crystallizing in a different form than
  aragonite. In shells it is translucent and more stable than aragonite.

Cambrian—the first (oldest) period of the Paleozoic era.

Calyx—in corals the bowl-shaped depression in the upper part of the
  skeleton; in stalked echinoderms that part of the body which contains
  most of the soft parts.

Caprinid—a Cretaceous pelecypod that is typically coiled in the form of
  a ram’s horn.

Carapace—the hard protective covering that forms the exoskeleton of many
  invertebrates; in arthropods it is usually chitinous or
  calcaro-chitinous.

Carbonization—the process of fossilization whereby organic remains are
  reduced to carbon or coal.

Cast—the impression taken from a mold.

Cenozoic—the latest era of geologic time, following the Mesozoic era and
  extending to the present.

Cephalon—the head; in trilobites the anterior body segment forming the
  head.

Cephalopod—marine invertebrate with well-defined head and eyes and with
  tentacles around the mouth; member of class Cephalopoda, phylum
  Mollusca; includes squids, octopuses, pearly nautilus.

Ceratite—an ammonoid cephalopod with suture composed of rounded saddles
  and jagged lobes; member of subclass Ammonoidea.

Chert—a cryptocrystalline variety of silica; flint is a variety of
  chert.

Chitin—a horn-like substance, found in the hard parts of many animals,
  such as beetles, crabs, etc.

Chitinous—composed of chitin.

Cirri—in crinoids, the jointed appendages which branch off the side of
  the stem or from the base of some crinoid stems.

Coelenterate—invertebrates characterized by a hollow body cavity, radial
  symmetry, and stinging cells; a member of phylum Coelenterata;
  includes jellyfishes, corals, sea anemones.

Colonial—in biology refers to the way in which some invertebrates live
  in close association with, and are more or less interdependent upon,
  each other; colonial corals, hydroids, etc.

Columella—a small column or central axis; in corals the small rod or
  axial pillar in the center of the corallite; in gastropods the solid
  or perforate pillar formed by the union of the successive coils of a
  conispiral shell.

Columnal—one of the disk-shaped segments of a crinoid stalk.

Concentric—having a common center, as circles; refers to shell markings
  that are parallel to shell margin.

Concretion—nodular or irregular masses in sedimentary rocks and usually
  formed around a central core, which is often a fossil.

Conical—cone-shaped.

Conodont—minute tooth-like fossils found in certain Paleozoic rocks;
  their origin is not definitely known, but they may have been part of
  some type of extinct fish.

Coral—bottom-dwelling marine invertebrate that secretes calcareous hard
  parts; member of class Anthozoa, phylum Coelenterata.

Corallite—the skeleton formed by an individual coral animal; may be
  solitary or form part of a colony.

Corallum—the skeleton of a coral colony.

Corona—crown; in echinoids the main part of the skeleton consisting of
  symmetrically arranged calcareous plates.

Coprolite—the fossil excrement of animals.

Correlation—the process of demonstrating that certain strata are closely
  related to each other or that they are stratigraphic equivalents.

Cretaceous—the third and last period of the Mesozoic era.

Cystoid—an extinct stemmed echinoderm with calyx composed of numerous
  irregularly arranged plates; member of class Cystoidea.

Dendritic—resembling a tree, branching.

Dentition—the system or arrangement of teeth peculiar to any given
  animal.

Devonian—the fourth oldest period of the Paleozoic era, follows the
  Silurian, precedes the Mississippian.

Dip—the angle of inclination which the bedding plane of rocks makes with
  a real or imaginary horizontal line.

Distillation—in fossils that process by which volatile organic matter is
  removed, leaving a carbon residue.

Dolomite—a mineral composed of calcium magnesium carbonate (CaMg(CO₃)₂).

Dorsal—pertaining to the back.

Echinoderm—a marine invertebrate with calcareous exoskeleton and usually
  exhibiting a five-fold radial symmetry; member of phylum
  Echinodermata; includes cystoids, blastoids, crinoids, starfishes, and
  sea urchins.

Echinoid—bottom-dwelling, unattached marine invertebrate with
  exoskeleton of calcareous plates covered by movable spines; member of
  class Echinoidea; sea urchins, heart urchins, biscuit urchins.

Endoskeleton—the internal supporting structure of an animal.

Eocene—the next to earliest of the Tertiary epochs, follows the
  Paleocene and precedes the Oligocene.

Equivalved—right and left valves subequal and (except for hinge
  structures) comprising mirror images of each other.

Evolution—a term applied to those methods or processes and to the sum of
  those processes whereby organisms change through successive
  generations.

Exoskeleton—an external skeleton, or hard covering for the protection of
  soft parts, particularly among invertebrates.

Fault—the displacement of rocks along a zone of fracture.

Fauna—an assemblage of animals (living or fossil) living in a given
  place at a given time.

Flank—the side or lateral portion of anything.

Flora—an assemblage of plants (living or fossil) living in a given place
  at a given time.

Fold—in brachiopods, a major rounded elevation of shell which affects
  both inner and outer shell surfaces.

Foramen—in brachiopods, the opening in the pedicle valve near the beak
  where the pedicle extends through the shell.

Foraminifer—a protozoan usually possessing a calcareous, perforated,
  chambered shell, but shell may be chitinous or agglutinated; a member
  of the order Foraminifera, phylum Protozoa.

Formation—a rock unit useful for mapping and distinguished primarily on
  the basis of lithologic characters.

Fossil—the remains or traces of organisms buried by natural causes and
  preserved in the earth’s crust.

_Guide fossil_—a fossil which, because of its limited vertical but wide
  horizontal distribution, is of value as a guide or index to the age of
  the rocks in which it is found.

Fossiliferous—containing fossilized organic remains.

Fusulinid—a spindle-shaped foraminifer: test shaped like a grain of
  wheat.

Gastrolith—highly polished well-rounded pebbles found associated with
  certain reptilian fossils; “stomach stones.”

Gastropod—a terrestrial or aquatic invertebrate, typically possessing a
  single-valved, calcareous, coiled shell; member of class Gastropoda,
  phylum Mollusca: snails and slugs.

Geologic age—the age of an object as stated in terms of geologic time
  (e.g., a Pennsylvanian fern, Cretaceous dinosaur).

Geologic map—map showing distribution of rock outcrops, structural
  features, mineral deposits, etc.

Geologic range—the known duration of an organism’s existence throughout
  geologic time (e.g., Cambrian to Recent for brachiopods).

Glauconite—a greenish mineral commonly formed in marine environments and
  essentially a hydrous silicate of iron and potassium.

Goniatite—an ammonoid cephalopod with suture composed of smooth saddles
  and simple angular lobes; member of subclass Ammonoidea.

Graptolite—an extinct, marine, colonial organism with chitinous hard
  parts; believed to belong to subphylum Hemichordata of phylum
  Chordata.

Guide fossil—see Fossil.

Habitat—the physical environment in which an organism lives.

Hinge-line—in brachiopods, the edge of the shell where the two valves
  articulate; in pelecypods, the dorsal margin of the valve which is in
  continual contact with the opposite valve.

Igneous rock—rocks which have solidified from lava or molten rock called
  magma.

Index fossil—see Fossil.

Inequivalved—opposite valves unlike in shape or size, or both.

Jurassic—second oldest period of the Mesozoic; follows the Triassic,
  precedes the Cretaceous.

Keel—a strong continuous ridge along the ventral side of ammonites.

Larva—the young form of some animals before they assume the mature
  shape.

Lateral—side or to the side.

Lithology—the study and description of rocks based on the megascopic
  (with the naked eye) examination of samples. Used also to refer to the
  texture and composition of any given rock sample.

Living chamber—in mollusks, that part of the shell which is occupied by
  the living animal.

Lobe—in cephalopods, the backward flexure of the suture or septum.

Longitudinal—in a direction parallel with the length.

Lophophore—in brachiopods, a tentacle-bearing appendage attached to the
  anterior surface of the mantle cavity.

Mantle—in mollusks and brachiopods, a layer of tissue containing cells
  that secrete the shell.

Meso-—a prefix signifying middle.

Mesozoic—that era of geologic time that precedes the Cenozoic and
  follows the Paleozoic.

Miocene—fourth oldest epoch of the Tertiary period; follows the
  Oligocene, precedes the Pliocene.

Mississippian—fifth oldest period of the Paleozoic: follows the
  Devonian, precedes the Pennsylvanian.

Multicellular—composed of more than one cell.

Nacreous—pearly.

Node—a knob.

-oid—a suffix meaning “in the form of.”

Oligocene—the third oldest epoch of the Tertiary period: precedes the
  Miocene, follows the Eocene.

Operculum—the lid or covering of the aperture of certain shells.

Oral—referring to the mouth or aperture.

Orbitoidids—foraminifers with large typically disk-shaped tests.

Ordovician—second oldest period of the Paleozoic era; follows the
  Cambrian, precedes the Silurian.

Ossicle—loosely used as a small plate.

Paleocene—oldest epoch of the Tertiary period; precedes the Eocene.

Paleozoic—that era of geologic time that follows Precambrian time and
  precedes the Mesozoic era.

Pedicle opening (pedicle foramen)—see Foramen.

Pelecypod—a bivalved aquatic invertebrate; member of class Pelecypoda,
  phylum Mollusca.

Pennsylvanian—the sixth oldest period of the Paleozoic era; follows the
  Mississippian, precedes the Permian.

Period—a division of geologic time (Pl. 1).

Periostracum—the horny outer covering or epidermis on shells.

Permian—seventh and last period of the Paleozoic.

Permineralization—that process by which mineral matter has been added to
  the original shell material by precipitation in the interstices rather
  than replacing the original shell material.

Phosphatic—containing or pertaining to phosphate minerals.

Phylum—one of the primary divisions of the animal or vegetable kingdoms.

Planispiral—shell coiled in one plane.

Pleistocene—earliest epoch of Quaternary period, Cenozoic era; follows
  Pliocene epoch of Tertiary period, precedes Recent epoch of
  Quaternary.

Pleural—referring to the side or ribs; in trilobites, refers to lateral
  portions of thorax and pygidium.

Pliocene—latest epoch of Tertiary period of Cenozoic era; follows
  Miocene epoch and precedes Pleistocene epoch of Quaternary period.

Polygonal—many sided or having many-sided plates.

Polyp—a many-tentacled aquatic coelenterate animal, typically
  cylindrical or cup-shaped, as in corals.

Porcelaneous—like porcelain.

Pore—a very small opening.

Posterior—situated behind; to the rear.

Precambrian—that portion of geologic time before the Cambrian; divided
  into Archeozoic era (Early Precambrian) and Proterozoic era (Late
  Precambrian).

Protero—combining form meaning fore, former, or anterior in time (Greek
  _proteros_, fore).

Proterozoic—youngest era of the Precambrian; follows the Archeozoic era
  and precedes the Cambrian period of the Paleozoic era.

Protista—the organic kingdom including the simplest of all one-celled
  organisms which possess various characters of both plants and animals;
  bacteria, algae, foraminifers, radiolarians.

Protoconch—in mollusks, the initial chamber of shell.

Pyrite—a hard, brass-yellow mineral composed of iron sulfide; “fool’s
  gold.”

Quaternary—the youngest period of the Cenozoic era, follows the Tertiary
  period.

Radial symmetry—see Symmetry.

Reef—a mound-like or ridge-like elevation of the sea bottom which almost
  reaches the surface of the water, composed primarily of organic
  material and commonly formed by reef-building animals, such as corals
  and oysters.

Replacement—type of fossilization whereby hard parts of organisms are
  removed by solution accompanied by almost simultaneous deposition of
  other substances in the resulting voids; mineralization.

Respiration—the process of oxygenation.

Rock—an aggregation of one or more minerals.

Rock-unit—divisions of rocks based on definite physical and lithologic
  characteristics and not defined on the basis of geologic time alone;
  groups, formations, members.

Rudistid—a Cretaceous pelecypod that does not exhibit the typical clam
  or oyster shape; many are cone-shaped, resembling corals.

Saddle—in cephalopods, the forward flexure (curved toward the aperture)
  of the suture or septum.

Scaphopod—an exclusively marine mollusk with a single-valved tusk-shaped
  shell; member of class Scaphopoda, phylum Mollusca.

Scavenger—an animal that feeds on organic refuse.

Sedentary—stationary in life, not moving from place to place.

Sediment—material that has been deposited by settling from a
  transportation agent such as water or air; typically composed of
  weathered rock fragments.

Sedimentary rock—rocks formed from the accumulation and lithification of
  sediments.

Segment—one of the parts into which a body naturally separates or is
  divided; for example, segments of arthropods or annelid worms.

Septal—pertaining to the septum.

Septum (plural, septa)—a dividing wall or partition; in fusulinids, a
  partition between chambers in the fusulinid shell; in corals, one of
  the radiating, longitudinal, calcareous plates located within the
  corallite; in cephalopods, the transverse partitions between the
  chambers.

Series—the rocks formed during an epoch; the time-stratigraphic term
  next in rank below a system.

Serrate—notched like a saw.

Sessile—animal attached to the sea floor more or less permanently.

Silica—an oxide of silicon (SiO₂).

Siliceous—containing or pertaining to silica.

Silicification—the process of combining or impregnating with silica.

Silurian—the third oldest period of the Paleozoic era; follows the
  Ordovician, precedes the Devonian.

Sinus—an elongate depression on brachiopod shells.

Siphuncle—in cephalopods, the segmented horny or calcareous tube which
  extends from the protoconch to the living chamber.

Slickensides—polished and grooved surfaces that are the result of two
  rock masses sliding past each other as in faulting.

Solitary—living alone; not part of a colony.

Species—one of the smaller natural divisions in classification.

Specific name—see Trivial name.

Spicule—a minute spike or dart, skeletal element in sponges and
  holothurians.

Stratum (plural, strata)—a single bed or layer of rock.

Strike—the direction of a real or imaginary line that is formed by the
  intersection of a bed or stratum with a horizontal plane; strike is
  perpendicular to the dip.

Subconical—less than conical in shape; almost a cone.

Suture—the line of junction between two parts; in crinoids, the line of
  junction between two plates; in gastropods, the line of junction of
  the whorls as seen on the exterior of the shell; in cephalopods, the
  line of junction between a septum and the shell wall.

Symmetry—orderly arrangement of parts of an object with reference to
  lines, planes, or points.

_Bilateral symmetry_—the symmetrical duplication of parts on each side
  of a vertical anterior-posterior plane.

_Radial symmetry_—the symmetrical repetition of parts around a common
  vertical dorso-ventrally disposed axis.

_Pentamerous symmetry_—symmetry arranged in a pattern of fives.

System—the rocks formed during a period; the time-stratigraphic term
  next in rank above a series.

Taxonomy—that branch of science that deals with classification,
  especially in relation to plants, animals, or fossils.

Tertiary—the oldest period of the Cenozoic era; follows the Cretaceous
  period of the Mesozoic and precedes the Quaternary period of the
  Cenozoic.

Test—the protective covering of some invertebrate animals.

Theca—a sheath or case; in coelenterates, the bounding wall at or near
  the margin of the exoskeleton; in echinoderms, the main body skeleton
  (or calyx) which houses the animal’s soft parts; in graptolites, any
  cup or tube of the colony.

Thorax—in trilobites, that part of the body between the cephalon and
  pygidium.

Time-unit—a portion of continuous geologic time (e.g., eras, periods,
  epochs, and ages).

Time-rock unit—same as time-stratigraphic unit.

Time-stratigraphic unit—term given to rock units with boundaries
  established by geologic time; strata deposited during definite
  portions of geologic time (e.g., systems, series, stages, etc.).

Topography—the physical features or configuration of a land surface.

Topographic map—a map showing the physical features of an area,
  especially the relief and contour of the land.

Transverse—at right angles to length.

Triassic—the youngest period of the Mesozoic era; follows the Permian
  period of the Paleozoic and precedes the Jurassic period of the
  Mesozoic.

Trilobite—an extinct marine arthropod having a flattened segmented body
  covered by a hardened dorsal exoskeleton divided into three lobes.

Trivial name—the Latinized name added to a generic name to distinguish
  the species; same as specific name.

Type locality—the geographic location at which a formation was first
  described and from which it was named; or from which the type specimen
  of a fossil species comes.

Type specimen—the individual or specimen on which the original
  designation of a species was established.

Umbilicus—an external depression or opening at the center of many
  loosely coiled shells; in gastropods it is usually located at the base
  of the shell; in cephalopods it is usually located laterally.

Umbo—the arched part of the valve near the beak in bivalve shells.

Unicellular—composed of one cell.

Valve—the one or more pieces comprising the shell of animals.

Variety—a subdivision of a species, designated by a third name when a
  variety is designated.

Ventral—pertaining to the abdomen; as opposed to dorsal, pertaining to
  the back.

Vertebrate—an animal having a backbone or spinal column.

Whorl—a single turn or volution of a coiled shell.

-zoic—combining form meaning “life” (Greek _zoikos_, life).

Zooecium (plural, zooecia)—tube or chamber occupied by an individual of
  the bryozoan colony; also called an autopore.




                               Footnotes


[1]Associate Professor of Geology, Lamar State College of Technology,
    Beaumont, Texas.

[2]Entries marked with asterisk are published by the Bureau of Economic
    Geology, The University of Texas, Austin. Those not out of print are
    distributed at nominal sale price; list sent on request. These
    publications may be consulted at many public libraries and/or
    Chamber of Commerce offices.




                                 Index


            Page numbers in italics indicate illustrations.


                                   A
  _Acanthoceras_: 77
  _Actinomma_: 49
  Africa: 87
  Agnatha: 87
  Alaska: 7
  _Alectryonia lugubris_: 68
  algae: 44, 46, 47
  “algal biscuits”: 44
  alligators: 95
  _Allorisma_: 67
  _Allosaurus_: 90, 97, 98
  Allotheria: 100
  allotherians: 100
  Amarillo College: 27
  amber: 7
  amblypods: 102
  _Ambocoelia_: 57
  _Amelanchier_: 48
  American Museum of Natural History: 2, 15, 96
  ammonites: 11, 75, 76, 77, 78
  Ammonoidea: 66
  ammonoids: 75, 76, 77, 78
  Amphibia: 89
  amphibians: 87, 92
  Amphineura: 56
  _Amphiscapha_: 61
  _Ancilla_: 64
  _Angulotreta_: 55, 56
  ankylosaurs: 90, 97, 99
  Annelida: 78
  annelids: 78
  _Anomia_: 74
  anteaters: 100
  Anthozoa: 49, 51
  _Apsotreta_: 55, 56
  aragonite: 11
  _Archelon_: 91
  _Archetectonica_: 64
  _Archaeopteryx_: 100
  Archeozoic, derivation and pronunciation: 33
  Archer County: 89
  _Archimedes_: 54
  _arietina, Exogyra_: 70
  Aristotle: 3
  Arizona: 7
  Arkansas: 37
  Arlington State College: 1, 27
  armadillos: 100, 102
  Aronow, Saul: 1
  Arthropoda: 78, 79, 80
  arthropods: 10, 78, 79, 80
      crustaceans: 79, 80
      insects: 7, 79
      ostracodes: 79, 80
      trilobites: 78, 80
  Articulata: 56
  Artiodactyla: 106
  artiodactyls: 106
      camels: 106
      entelodonts: 101, 106
  ash, volcanic: 5
  _Astacodes_: 79
  _Astartella_: 67
  Asteroidea: 82
  asteroids: 82, 83
  Asterozoa: 82
  _Astraeospongium_: 50
  _Astrhelia_: 53
  _Astylospongia_: 50
  _Aulosteges tuberculatus_: 12, 13
  Austin: 14, 17, 19, 87
  Austin College: 27
  Australia: 87
  author, of a fossil: 22
  autopores: 51
  Aves: 89, 100
  _Avonia_: 12, 13
      _signata_: 12, 13
      _subhorrida_: 12, 13


                                      B
  bacteria: 47
  _Baculites_: 77
  bags, collecting: 17, 18
  Balcones fault zone: 36, 37
  baluchitheres: 104, 106
  _Baluchitherium_: 106
  _Barbatia_: 74
  Baylor County: 89
  Baylor University: 1, 2, 27, 90, 91, 95
  Beaumont: 1, 34
      clay: 34
  Beaver, Harold: 1
  _Belemnites_: 77, 78
  Belemnoidea: 78
  belemnoids: 77, 78
  _Bellerophon_: 61
  Big Bend area: 35, 36
      National Park: 35, 97, 102
  Big Spring: 89
  binomial nomenclature: 21-22
  Bird, R. T.: 2, 15, 96
  birds, fossil: 5, 100
  Blastoidea: 81
  blastoids: 26, 28, 81
  Blinn College: 27
  bone, permineralized: 9
  Books About Fossils: 108-110
  Boon, Jack: 1
  Brachiopoda: 54, 55, 56
  brachiopods: 26, 29, 54, 55, 56
      articulate: 54, 55, 56, 57, 58
      Cambrian: 55
      Cretaceous: 56
      inarticulate: 55, 56
      Mississippian: 55
      Pennsylvanian: 57, 58
      Permian: 12, 13
      Recent: 56
      silicified: 12, 13
      symmetry: 24, 26, 29
  _Brachiosaurus_: 90
  Brewster County: 11, 12, 35, 41
  brittle stars: 82
  Bronaugh, Richmond L.: 1
  Brontosaurus: 90, 97, 98
  _Brontotherium_: 104, 105, 106
  Brown, L. F., Jr.: 1
  Bryophyta: 44
  Bryozoa: 51, 54, 55
  bryozoans: 26, 27, 28, 30, 51, 54, 55, 84
      Mississippian: 54
      Pennsylvanian: 55
  _bulla, Venericardia_: 72
  Bureau of Economic Geology: 2, 19
  burrows: 14
  “button corals”: 49, 53


                                      C
  _Calamites_: 48
  calcite: 10, 11
  callus: 59
  _Calyptraphorus_: 64
  _Camarotoechia_: 55
  Cambrian—
      derivation and pronunciation: 34
      fossils: 40
          brachiopods: 55
          graptolites: 86
      of Franklin Mountains, Llano, Marathon, and Solitario uplifts:
          40
  camels: 106
  _cameratus, Neospirifer_: 58
  _Caninia_: 51, 52
  _Canis diris_: 102, 103
      _domestica_: 22
  caprinid: 27, 30
  caprock, of High Plains: 35
  carbon residues: 10, 86
  Carboniferous: 34
  _carinata, Ostrea_: 71
  Carnivora: 102
  carnivores: 102, 103
  _Caryocorbula_: 74
  _Caryocrinites_: 81
  Casey, Josephine: 2
  casts: 11
  catalog, fossil; number: 31
  cement, portland: 19
  Cenozoic—
      derivation and pronunciation: 33
      periods of: 34
      rocks in Texas: 43
  central Asia: 106
  central Texas: 11, 42
  Cephalopoda: 56, 66, 75, 78
  cephalopods: 24, 26, 27, 28, 29, 30, 66, 75, 76, 77, 78
      ammonites: 75, 76, 77, 78
      ammonoids: 75, 76, 77, 78
      belemnoids: 77, 78
      ceratites: 75, 78
      coleoids: 77, 78
      cuttlefish: 78
      goniatites: 75, 76
      nautiloids: 66, 75, 76
      octopus: 66, 78
      squid: 66, 78
      sutures: 66, 75, 78
  ceratites: 75, 78
  ceratopsians: 90, 99, 100
  _Ceratosaurus_: 90
  _Cerithium_: 62
  chalicotheres: 104, 106
  Chelonia. _See_ turtles.
  chisels: 17
  chitin: 10
  chitons: 56
  Chondrichthyes: 87
  _Chonetes_: 57
  Chordata: 84-102
  chordates: 84
      amphibians: 89, 92
      birds: 100
      fishes: 87, 88, 89
      graptolites: 40, 84, 86
      mammals: 100-107
      reptiles: 89-100
  _Cladochonus_: 51, 52
  _Cladophyllia_: 53
  clams: 11, 56, 59. _See also_ pelecypods.
  class, taxonomic: 22
  classification, binomial nomenclature: 21-22
      units of: 22
  club mosses: 47
  coal: 20, 47
      mines: 20, 47
      plants: 16, 46, 47, 48
  _Cochlespiropsis_: 63
  Coelenterata: 49, 51, 84
  coelenterates: 49, 51-_53_
  Coleoidea: 66
  coleoids: 77, 78
  collecting bags: 17, 18
  columella, corals: 51
      gastropods: 59, 60
  columnal, crinoid: 81, 82, 83
  Comanchean series of Cretaceous: 34. _See also_ Lower Cretaceous.
  compass: 19
  _Composita subtilita_: 57
  compound corals. _See_ corals, colonial.
  concretions: 16
  coniferous trees: 7
  conodonts: 41, 88, 89
  _Conus_: 63
  Cooper, G. A.: 2, 12
  coprolites: 14
  corallite: 49, 51
  corallum: 51
  corals: 11, 24, 26, 27, 49, 51, 52, 53
      “button”: 49, 53
      colonial: 24, 27, 30, 51, 52, 53
      Cretaceous: 53
      “horn”: 49, 51, 52
      morphology: 51
      Pennsylvanian: 52
      polyp: 49
      solitary: 24, 28, 29, 30, 49, 51, 52, 53
      symmetry: 24, 26, 27, 28, 29, 30
      Tertiary: 53
  _Cordaites_: 48
  correlation: 32
  _Corythosaurus_: 90
  cotylosaurs: 89, 92
  crabs: 78, 79
  _Crassatella_: 72
  crayfish: 78
  creodonts: 102
  Cretaceous—
      _See also_ Comanchean and Gulf series.
      derivation and pronunciation: 34
      fossils: 42-43
          arthropods: 79
          brachiopods: 56
          cephalopods: 66, 67, 76, 77
          corals: 53
          crocodiles: 95, 96
          dinosaurs: 90, 91, 93, 94, 95, 97, 99
          echinoderms: 83, 84, 85
          foraminifers: 49
          gastropods: 59, 62
          nautiloids: 76
          pelecypods: 59, 66, 68-_71_
          shark teeth: 88
          worms: 78
              tubes: 9
      of central Texas, Edwards Plateau, Gulf Coastal Plain, High
          Plains, north Texas, and Trans-Pecos Texas: 42
      “Pyrite Fossil Zone” of: 11
  crinoidal limestone: 41, 82, 83
  Crinoidea: 81
  crinoids: 26, 28, 41, 81, 82, 83
      calyx: 81, 82, 83
      morphology: 81
      stems: 26, 28, 81, 82, 83
  Crockett County: 42
  Crockett formation: 43
  crocodiles: 95, 96
  crossopterygians: 87
  crustaceans: 79, 80
  Culberson County: 35
  cuttlefish: 78
  cycads: 47, 48
  _Cymatoceras_: 75, 76
  Cystoidea: 81
  cystoids: 81, 82, 83


                                      D
  “Dark Ages”: 3
  da Vinci, Leonardo: 3
  Davis, Darrell: 1
  Decapoda. _See_ Coleoidea.
  deer: 106
  Del Mar College: 27
  dendrites: 14
  _Dendrograptus_: 86
  Denver, Colorado: 19
  _Derbya_: 57
  Devonian—
      derivation and pronunciation: 34
      fossils: 41
          placoderms: 87, 88
          _Psilophyton_: 48
      of El Paso and Van Horn regions, Llano and Marathon uplifts:
          41
  Diablo Mountains: 41
  diatoms: 44, 46, 47
  Dibranchiata. _See_ Coleoidea.
  _Dictyoclostus_: 55
  _Dimetrodon_: 92
  _Dinobastis_: 102, 103
  Dinocerata: 102
  dinocerates: 102, 105
  dinosaurs: 89, 90-_94_, 95, 96, 97, 98, 99, 100
      armored: 90, 97, 99, 100
      duck-billed: 90, 97, 99
      flying: 91, 94, 95
      horned: 90, 99, 100
      plate-bearing: 90, 97, 99
      swimming: 91, 93, 95
  _Diplodocus_: 90
  _Diplograptus_: 86
  dire wolf: 102, 103
  _diris, Canis_: 102, 103
  distillation: 10
  _Distorsio_: 63
  division, plant: 44
  Dixon, J. W., Jr.: 2, 90, 91
  dolomite: 11
  dolphins: 95
  _domestica, Canis_: 22
  DuBar, Jules: 1
  _Dufrenoyia_: 77


                                      E
  Eastland County: 20
  East Texas State College: 27
  Echinodermata: 80-84
  echinoderms: 80-84
      asteroids: 82, 83
      blastoids: 81
      crinoids: 81, 82, 83
      cystoids: 81, 82, 83
      echinoids: 82, 84, 85
      holothuroids: 84
          sclerites: 83
  Echinoidea: 82
  echinoids: 26, 28, 29, 82, 84, 85
      Cretaceous: 84, 85
      plates: 84, 85
      spines: 84, 85
  Echinozoa: 82
  Edentata: 100
  edentates: 100, 101, 102
  Edwards Plateau: 19, 36, 37, 42, 43
  Egyptian desert: 3
  _Elasmosaurus_: 91
  elephants: 102
  Eleutherozoa: 82
  Ellison, Samuel P.: 1
  El Paso region—
      Devonian of: 41
      Ordovician of: 40
      Precambrian of: 40
      Silurian of: 40
  _Endopachys_: 53
  _Enoploclytia_: 79
  entelodont: 101, 106
  _Eohippus._ _See_ _Hyracotherium_.
  epoch, geologic: 33
  era, geologic: 33-34
  Erath County: 20
  _Eryops_: 92
  _Euomphalus_: 61
  _Euphemites_: 62
  Europe: 89
  _Exogyra arietina_: 70
      _laeviscula_: 70
      _ponderosa_: 70
      _texana_: 70


                                      F
  “false fossils”: 14
  family, taxonomic: 22
  “feather stars”: 82
  ferns: 47, 48
  fish: 87, 88, 89
      armored: 41, 88
      carbon residue: 9
      scales: 10
      teeth: 10
      vertebrae: 10
  _Fistulipora_: 55
  _Flabellum_: 53
  foramen, pedicle: 54, 56
  Foraminifera: 47, 49
      Cretaceous: 49
      fusulinids: 26, 29, 49
      orbitoid: 26, 28
      Pennsylvanian: 49
  forams: 26, 28, 29, 47, 49
  formation, geologic: 34
  fossil—
      birds: 5, 100
      burrows: 14
      cataloging: 31
      collecting: 17
          equipment: 17
          ethics: 20
          how to collect: 20
          where to look: 19
      definition: 3
      dung: 14
      footprints: 14
      gizzard stone: 14
      identification: 21, 23-30
          keys: 26-30
      preservation—
          altered hard parts: 10-11
              carbonization: 9, 10
              mineralization: 10
              permineralization: 10
              petrifaction: 10
              replacement, calcareous, iron, siliceous: 10, 11, 13
          kinds of: 7
          original hard and soft parts: 7
      record, missing pages in: 5
      wood: 47
  fossilization, requirements of: 5
  fossils—
      animal: 47-107
      Cambrian: 40
      carbonized: 10
      classification of: 21-22
      cleaning: 21
      etching in acid: 21
      frozen: 5, 7, 104
      guide and/or index: 32
      in amber: 7
      in oil saturated soil: 7
      in quicksand: 5
      in tar: 5
      in volcanic ash: 5
      main types of: 44
      natural mummies: 7
      permineralized or petrified: 10
      plant: 4, 10, 20, 32, 44-48
      Pleistocene: 101, 102, 103, 104
      Precambrian: 40
      preparation of: 21
      Quaternary: 43, 101, 102, 103, 104
      replaced or mineralized: 10
      silicified: 21
          Cretaceous: 11
          Permian: 11
          etching: 21
      Silurian: 40, 81
      Tertiary: 43
      Triassic: 42
      uses of: 31-32
  France: 106
  Franklin Mountains, Cambrian of: 40
  frogs: 89
  _Frondicularia_: 49
  fungi: 44
  Fusselman limestone: 40
  _Fusulina_: 49
  fusulinids: 26, 29, 47, 49
  _Fusus_: 63


                                      G
  Gaptank formation: 35, 41
  gastroliths: 14
  Gastropoda: 56, 59
  gastropods: 26, 27, 29, 30, 56, 59, 60
      Cretaceous: 59, 62
      morphology: 60
      ornamentation: 59
      Pennsylvanian: 61, 62
      Tertiary: 59, 63, 64
  generic name: 21-22
  genus: 21-22
  geologic—
      column: 33
      history: 33
      map, definition: 40
      map of Texas: 38-39
      time: 34
      time scale: frontispiece, 33
  geology of Texas: 37-43
  Germany: 5, 100
  _Gingko_: 47, 48
  _Girtyocoelia_: 50
  Glasscock County: 42
  Glass Mountains: 11, 12, 35, 41, 42
  glauconite: 11
  _Globigerina_: 49
  Glossary: 111-114
  _Glycymeris_: 74
  _Glyptodon_: 101, 102
  glyptodont: 101, 102
  goats: 106
  goniatites: 75, 76
  Grand Prairie: 36, 37
  Graptolithina: 84, 86
  graptolites: 27, 30, 40, 84, 86
      of Marathon uplift: 40, 86
  Graptozoa. _See_ graptolites.
  _graysonana, Gryphaea_: 69
  Great Flood: 3
  ground sloths: 7, 101, 102
  _Gryphaea graysonana_: 69
      _washitaensis_: 69
  Guadalupe Mountains, Peak: 35
  Gulf Coast: 32
  Gulf Coastal Plain of Texas: 35, 36, 37, 42, 43, 106
  Gulf of Mexico: 37
  Gulf series of Cretaceous: 34. _See also_ Upper Cretaceous.
  _Gyrodes_: 62


                                      H
  hagfish: 87
  hammer, geologist’s: 17, 18
  _Hamulus_: 78
  hand lens: 17, 18
  hard parts, animal—calcareous, chitinous, phosphatic, siliceous
          remains: 10
  Hardin-Simmons University: 27
  heart urchins: 82, 83
  _Heliospongia_: 50
  hematite: 11
  _Hemiaster_: 85
  Hemichordata: 84
  Henderson County Junior College: 27
  Herodotus: 3
  _Heterostegina_: 32
  _Heteralosia hystricula_: 12, 13
  “het” zone: 32
  Hexacoralla: 51
  High Plains: 35, 36, 37, 42, 43, 89, 95, 106
  hippopotamuses: 106
  _Holaster_: 85
  _Holectypus_: 85
  Holothuroidea: 82
  holothuroids: 84
      sclerites: 83
  _Homo sapiens_: 22
  “horn corals”: 49, 51, 52
  horses: 103, 104
      teeth: 104
  Howard County Junior College: 27
  Hudspeth County: 35, 41, 42
  Hueco Mountains: 41
  Hughes, Jack T.: 1
  hydroids: 49
  Hydrozoa: 49, 84
  _Hyracotherium_: 103, 104
  _hystricula, Heteralosia_: 12, 13


                                      I
  ichthyosaurs: 91, 93, 95
  _Ichthyosaurus_: 91, 93
  identification keys, fossil: 26-30
      use of: 23-27
  igneous rocks: 5, 19
  Inarticulata: 54, 56
  _Inoceramus_: 69
  insects: 7, 78, 79
      in amber: 7
  iron, replacement by: 11
  Italy: 3


                                      J
  Jack County: 20
  jellyfish: 5, 49
  Jurassic—
      derivation and pronunciation: 34
      fossils: 42
          birds: 100
          dinosaurs: 90, 91, 95, 97, 98, 99
          _Gingko_: 48
      of Hudspeth County and/or Malone Mountain: 41
  _Juresania_: 58


                                      K
  keys. _See_ identification keys.
  Kilgore College: 27
  _Kingena wacoensis_: 56


                                      L
  labels, paper: 19
  _laeviscula, Exogyra_: 70
  Lamar State College of Technology: 1, 2, 27
  lampreys: 87
  _Latirus_: 63
  Lee College: 27
  _Lepidodendron_: 46
  _Levifusus_: 64
  _Lima_: 72
  limonite: 11
  _Lingula_: 55, 56
  Linnaeus: 21
  Linné: 21
  _Linoproductus_: 57
  _lisbonensis, Ostrea_: 72
  liverworts: 44
  lizards: 89
  Llano uplift: 36, 37, 40, 41
  Lonsdale, John T.: 1
  lophophore, brachiopod: 54
  _Lophophyllidium_: 49, 51, 52
      _proliferum_: 52
      _radicosum_: 52
  Los Angeles, California: 5
  Louisiana: 37
  Lower Cretaceous: 34, 42, 56, 97. _See also_ Comanchean.
  _lugubris, Alectryonia_: 68
  _Lunatia_: 62
  lungfishes: 87


                                      M
  Macon, J. W.: 2
  magnifying glass: 17, 18
  Malone Mountain: 42
  Mammalia: 89, 100-107
  mammoths: 102, 104, 107
      frozen: 7, 102
      tooth: 104
      woolly: 102, 104, 107
  mantle, brachiopod: 54
      pelecypod: 59
  maps—
      county: 17
      geologic: 19
          of Texas: 38-39
      physiographic of Texas: 36
      topographic: 19, 20
  Marathon uplift: 35, 36, 40, 41
  marcasite: 11
  _Marginifera_: 57
      _opima_: 12, 13
  mastodon, tooth: 104
  _Meandrostia_: 50
  Mediterranean Sea: 3
  _mercenaria, Venus_: 22
  _Mesalia_: 63
  _Mesolobus_: 57
  Mesozoic—
      derivation and pronunciation: 33
      periods of: 34
      rocks in Texas: 42-43
  metamorphic rocks: 5, 19
  _Metoicoceras_: 76
  _Michelinia_: 52
  _Micrabacia_: 49, 52
  microfossils: 4, 10, 32, 47, 49, 50, 78
  micropaleontological slides: 32
  micropaleontologist: 32, 47, 80
  micropaleontology: 4, 89
  Midwestern University: 27
  mine dumps: 20, 47
  Mississippian—
      derivation and pronunciation: 34
      fossils: 41
          blastoid: 81
          brachiopods: 55
          bryozoan: 54
      of Hueco Mountains: 41
      of Llano region: 41
  mold, external: 9, 11, 59, 66
      internal: 9, 11, 59, 62, 66
  Mollusca: 56-78
  mollusks: 7, 56, 59-78. _See also_ Mollusca.
  _Moropus_: 106
  mosasaur: 91, 93, 95
  “moss animals”: 54
  mosses: 44
  _Muirwoodia multistriatus_: 12, 13
  multituberculates: 100
  _multistriatus, Muirwoodia_: 12, 13
  mussels: 56, 59
  museums, as aid in identification: 23
      American, Natural History: 2, 15, 96
      Strecker: 95
      Texas Memorial: 14, 87, 95, 97, 100, 102
  _Myalina_: 67
  _Mylodon_: 100, 101


                                      N
  Nautiloidea: 66
  nautiloids: 66
      Cretaceous: 76
      morphology: 75
      Pennsylvanian: 76
      sutures: 75
  _Nautilus_: 66
      morphology: 75
  _Neithea_: 70
  _Neospirifer_: 57
      _cameratus_: 58
  _Nerinea_: 62
  _Neuropteris_: 48
  _Neverita_: 64
  New Mexico: 7
  New York City: 14
  North-Central Plains: 35, 36, 37, 40, 41, 42, 43
  north Texas: 42
  North Texas State College: 27
  notebook, field: 17
  _Notopocorystes_: 79, 80
  _Nucula_: 73
  _Nuculana_: 67
  _Nuculopsis_: 67


                                      O
  octopus: 66, 78
  Odessa College: 27
  operculum: 59
  _Ophiuroidea_: 82
  ophiuroids: 82
  _opima, “Marginifera”_: 12, 13
  order, taxonomic: 22
  Ordovician—
      derivation and pronunciation: 34
      fossils: 40
          graptolites: 86
      of El Paso region, Llano, Marathon, Solitario, and Van Horn
          uplifts: 40
  ornamentation, brachiopod: 54
      gastropod: 59
      pelecypod: 66
  Ornithischia: 97
  ornithischians: 90, 97, 98, 100
  Ornithopoda: 97
  ornithopods: 90, 97, 99
  _Orthoceras_: 66, 76
  _Orthoyoldia_: 73
  ossicles. _See_ sclerites.
  _Osteichthyes_: 87
  Ostracoda: 80
  ostracoderms: 87
  ostracodes: 78, 79, 80
  _Ostrea carinata_: 71
      _lisbonensis_: 72
      _quadriplicata_: 71
      _sellaeformis_: 72
  _Oxytropidoceras_: 77
  oysters: 56, 59


                                      P
  _Pachecoa_: 72
  _Pachymya_: 71
  paleobotany: 4
  paleobotanists: 44
  paleontology—
      definition: 4
      divisions of: 4
      history of: 3
      invertebrate: 4
      vertebrate: 4
  _Paleoscincus_: 90, 97, 99, 100
  Paleozoic—
      derivation and pronunciation: 33
      periods of: 34
      rocks of Texas: 40-42
  Palo Pinto County: 20
  Paluxy Creek: 14, 15
  Pan American College: 27
  Pantodonta: 102
  pantodonts: 102
  _Parasaurolophus_: 90
  _Parasmilia_: 53
  Parker County: 20
  Pawpaw formation: 11
  pearly nautilus: 66
      morphology: 75
  Pecos County: 42
  Pecos River valley: 35
  _Pecten_: 59, 68, 74
  pedicle: 54, 56
      foramen: 54, 56
      valve, brachiopod: 54
  Pelycosaurs: 89, 92
  Pelecypoda: 56, 59, 65-66
  pelecypods: 26, 29, 30, 56, 59, 60, 66
      Cretaceous: 59, 66, 68-_71_
      dentition: 66
      morphology: 59, 60, 65, 66
      ornamentation: 66
      Pennsylvanian: 66, 67
      teeth: 60, 65, 66
      Tertiary: 72, 73, 74
  Pelmatozoa: 80, 81
  Pennsylvanian—
      derivation and pronunciation: 34
      fossils: 41
          brachiopods: 57, 58
          bryozoans: 55
          cephalopods: 66, 76
          corals: 52
          crinoids: 41, 82, 83
          fusulinids: 47, 49
          gastropods: 61, 62
          nautiloids: 76
          pelecypods: 66, 67
          plants: 46, 47, 48
          shark teeth: 87
          sponges: 50
      of Diablo and Hueco Mountains, Llano and Marathon uplifts, and
          north-central Texas: 41
  _Pentaceros_: 83
  _Pentagonaster_: 83
  _Pentremites_: 81
  period, geologic: 33
  periostracum: 60
  Perissodactyla: 104
  perissodactyls: 103, 104, 105
  Permian—
      derivation and pronunciation: 34
      fossils: 41
          amphibian: 89, 92
          brachiopods: 12, 13
          cotylosaurs: 89, 92
          pelycosaurs: 89, 92
      of Glass Mountains: 11, 12, 35
  _permiana, Prorichthofenia_: 12, 13
  permineralized bone: 9
  petroleum geologist: 4
  _Phaneroceras_: 76
  _Phobosuchus_: 95, 96
  _Pholadomya_: 71, 72
  phyla: 22
  _Phyllograptus_: 86
  phylum: 22
  physiographic provinces, of Texas: 35-37
  physiography, definition: 35
      of Texas: 35-37
  phytosaurs: 42, 91, 94, 95
  pick, mineralogist’s or prospector’s: 17, 18
  pigs: 106
  _Pinna_: 67
  Pisces: 86-89
  _Pitar_: 72
  Placodermi: 87
  placoderms: 87, 88
  plant kingdom: 44
  plants, classification: 44
      Pennsylvanian: 46, 47, 48
  _Platyceras_: 62
  Pleistocene: 43. _See also_ Quaternary.
      fossils: 101, 102, 103, 104
  plesiosaurs: 91, 93, 95
  _Pleurocora_: 53
  _Plicatula_: 68, 74
  _Pliohippus_: 103
  Poland: 7, 106
  pollen: 47
  polyp, coral: 49
  _Polypora_: 55
  _ponderosa, Exogyra_: 70
  Porifera: 49
  _Porodiscus_: 49
  portland cement: 19
  Precambrian—
      definition: 34
      fossils: 40
      of El Paso region: 40
      of Llano uplift: 37, 40
      of Van Horn uplift: 40
      rocks of Texas: 40
  Presidio County: 35
  Proboscidea: 102
  proboscideans: 102, 104, 107
      teeth: 104
  _proliferum, Lophophyllidium_: 52
  _Prorichthofenia permiana_: 12, 13
  Proterozoic, derivation and pronunciation: 33
  Protista: 47
  _Protocardia_: 68
  _Protoceratops_: 90
  Protozoa: 47, 49
  protozoans: 47
  pseudofossils: 14
  _Pseudoliva_: 63
  _Psilophyton_: 48
  _Pteranodon_: 91, 94
  Pterodactyloids: 91
  pterosaurs: 91, 94, 95
  _Punctospirifer_: 57
  pyrite: 11
  “Pyrite Fossil Zone” of Cretaceous: 11


                                      Q
  _quadriplicata, Ostrea_: 71
  quarries: 19
  Quaternary—
      derivation and pronunciation: 34
      fossils: 43, 101, 102, 103, 104
      of Edwards Plateau, Gulf Coast, High Plains, North-Central
          Plains, and Trans-Pecos Texas: 43
  quicksand: 5


                                      R
  _radicosum, Lophophyllidium_: 53
  Radiolaria: 47
  radiolarians: 47, 49
  Rancho La Brea tar pit: 5
  rays: 87
  Reagan County: 42
  _Receptaculites_: 50
  Renaissance: 3
  Reptilia: 89-100
  reptiles: 89-100
  rhamphorhynchoids: 91
  _Rhamphorhynchus_: 91, 94
  rhinoceroses: 7, 104, 106, 107
      woolly: 106, 107
  _Rhipodomella_: 55
  _Rhombopora_: 51, 55
  Rice University: 27
  Rio Grande valley, of Trans-Pecos: 35, 95
  road metal: 19
  _Robulus_: 49
  Rock and Mineral Clubs: 23
  rock units: 34
  _rockymontanus, Spirifer_: 58
  Rodda, Peter U.: 1
  rudistids: 26, 27, 28, 29, 30
  Rugosa: 51


                                      S
  saber-tooth cat: 102, 103
  St. Mary’s University: 27
  salamanders: 89
  _Salenia_: 85
  San Angelo College: 27
  San Antonio College: 27
  sand dollars: 82
  _sapiens, Homo_: 22
  Sarcodina: 47
  Saurischia: 97
  saurischians: 90, 97, 99
  Sauropoda: 97
  sauropods: 90, 97, 98
  scale trees: 46, 47
  scallops: 56, 59
  Scaphopoda: 56
  scaphopods: 26, 27, 28, 29, 56
  _Schizodus_: 67
  scientific names: 21-23
  Scleractinia: 51
  sclerites, holothurian: 83, 84
  scolecodont: 78
  scouring rushes: 47, 48
  Scyphozoa: 49, 84
  sea anemones: 49
  sea cucumbers: 82
  “sea lily”: 81, 82
  “sea mats”: 51, 54
  “sea-mice”: 56
  sea urchins: 82
  sedimentary rocks: 5, 19
  _sellaeformis, Ostrea_: 72
  septa, cephalopods: 66, 75
      corals: 49, 51
  serpent stars: 82
  _Serpula_: 78
  _Seymouria_: 92
  sharks: 87
      teeth: 10, 87, 88
  sheep: 106
  shrimp: 78
  Siberia: 7, 106
  _Sigillaria_: 46
  _signata, Avonia_: 12, 13
  silica: 10, 11
  silicification: 11
  Silurian—
      derivation and pronunciation: 34
      fossils: 40
          cystoid: 81
      of El Paso and Van Horn regions: 40
  skates: 87
  slickensides: 16
  slugs: 56
  Smith, Fred: 1
  snails: 11, 56, 59. _See also_ gastropods.
  snakes: 89
  Solitario uplift: 40
  Somervell County: 14, 15
  South America: 87, 102
  Southern Methodist University: 27
  South Texas College: 27
  Southwestern University: 27
  species: 22
  spicules, sponge: 49, 50
  spiders: 78
  spines, echinoid: 84, 85
  _Spirifer rockymontanus_: 58
  _Spirorbis_: 78
  sponges: 10, 27, 30, 49, 50
  spores: 47
  _Squamularia_: 57
  squid: 66, 78
  starfish: 82, 83
  _Stegosaurus_: 90, 97, 99
  stegosaurs: 90, 97, 99
  steinkern: 59, 62
  stems, crinoid: 26, 28, 41, 81, 82, 83
  Stephen F. Austin State College: 27
  “stomach stones”: 14
  stone, building: 19
  Strabo: 3
  _Straparolus_: 61
  Strecker Museum: 95
  _Striatopora_: 51, 52
  _Strobeus_: 62
  Styracosaurus: 90
  _subhorrida, Avonia_: 12, 13
  _subtilita, Composita_: 57
  Sul Ross State College: 27
  _Surcula_: 64
  sutures, cephalopod: 66, 75, 78
      nautiloid: 75
  swine, giant: 106
  _Sycostoma_: 64
  symmetry: 23
      bilateral: 24, 26, 29
      radial: 24, 26, 28, 80


                                      T
  tabulae: 51
  Tabulata: 51
  tape, masking: 19
  tapirs: 104
  tar: 5
  Tarleton State College: 27
  Tarrant County: 11
  taxonomy: 21-22
  teeth, horse: 104
      mammoth: 104
      shark: 10, 87, 88
  _Tellina_: 73
  Tertiary—
      derivation and pronunciation: 34
      fossils: 43
          corals: 53
          gastropods: 59, 63, 64
          mammals: 100-107, 103, 105
          microfossils: 32
          pelecypods: 72, 73, 74
          radiolarians: 49
          rocks of Gulf Coastal Plain, High Plains, North-Central
          Plains, and Trans-Pecos region: 42
  Tetracoralla: 51
  Tetrapoda: 86, 89-107
  _texana, Exogyra_: 70
  _Texanites_: 77
  Texas A. & M. College: 1, 27
  Texas Christian University: 27
  Texas College: 27
  Texas College of Arts and Industries: 27
  Texas Highway Department: 17
  Texas Memorial Museum: 14, 87, 95, 97, 100, 102
  Texas Technological College: 27
  Texas, the geology of: 34, 37-43
  Texas Western College: 27
  Thallophyta: 43, 46
  Theophrastus: 3
  Therapsids: 89
  Theria: 100
  therians: 100-107
      artiodactyls: 101, 106
      carnivores: 102, 103
      dinocerates: 102, 105
      edentates: 100, 101, 102
      pantodonts: 102
      perissodactyls: 104
      proboscideans: 102, 104, 107
  Theropoda: 97
  theropods: 90, 97, 98
  The University of Texas: 1, 2, 27
  time, geologic: 34
  titanotheres: 104, 105, 106
  toads: 89
  tortoises: 89
  traces of organisms: 14
      burrows: 14
      coprolites: 14
      gastroliths: 14
      tracks: 14, 15
      trails: 14
  Tracheophyta: 44, 46, 48
  _Trachodon_: 90, 97, 99
  tracks, dinosaur: 14, 15, 97
  Trans-Pecos region: 35, 36, 40, 42, 43, 86, 95, 102, 106
  tree sloths: 100, 102
  trees, coniferous: 7
  _Trepospira_: 61
  Triassic—
      derivation and pronunciation: 34
      fossils: 42
          dinosaurs: 95
          phytosaurs: 91, 94, 95
      of Crockett, Glasscock, Pecos, Reagan, and Upton counties;
          Glass Mountains and High Plains: 42
  _Triceratops_: 90, 99, 100
  _Trigonia_: 69
  Trilobita: 78
  trilobites: 78, 80
      morphology: 80
  Trilobitomorpha: 78
  _Trinacromerum_: 91
  Trinity University: 27
  trivial name: 21-22
  _Trochosmilia_: 53
  _Tuba_: 64
  _tuberculatus, Aulosteges_: 12, 13
  _Turrilites_: 77
      _worthensis_: 22
  _Turritella_: 62, 63
  turtles: 89, 91
  tusk-shells: 56
  Tyler Junior College: 27
  _Tylosaurus_: 91, 93
  _Tylostoma_: 62
  _Tyrannosaurus_: 90, 97


                                      U
  uintatheres: 102, 105
  _Uintatherium_: 102, 105
  umbilicus: 59, 60
  United States Geological Survey: 19
  United States National Museum: 2, 12
  University of Corpus Christi: 27
  University of Houston: 1, 27
  University of Texas, The: 1, 2, 27
  Upper Cretaceous: 34, 42, 78. _See also_ Gulf.
  Upton County: 42


                                      V
  valves, brachiopod: 54, 56
      pelecypod: 59, 65, 66
  Van Horn uplift: 35, 36, 40, 41
  _Venericardia_: 73
      _bulla_: 72
  ventral valve, brachiopod: 54
  _Venus mercenaria_: 22
  _Vertagus_: 63
  Vertebrata: 84, 86-107
  vertebrates: 86-107
      amphibians: 89, 92
      birds: 100
      fish: 87, 88, 89
      mammals: 100-107
      reptiles: 89-100
  _Vokesula_: 73
  volcanic ash: 5
  _Volutolithes_: 64


                                      W
  Waco: 91, 92, 95
  _wacoensis, Kingena_: 56
  Washington, D. C.: 19
  _washitaensis, Gryphaea_: 69
  Weches formation: 43
  West Texas State College: 1, 27
  Wilson, John A.: 2
  Wilson, Sarah Louise: 2
  Wise County: 20
  wood, petrified: 19
  Woodbine: 10, 37, 47
  worms, annelid, fossil, segmented: 78
  worm tubes, Cretaceous: 9
  _Worthenia_: 61
  _worthensis, Turrilites_: 22


                                      Y
  _Yoldia_: 67
  Young County: 20
  Young, Keith: 1


                                      Z
  Zoantharia: 51
  zooecia: 51




                          Transcriber’s Notes


--Retained publication information from the printed edition: this eBook
  is public-domain in the country of publication.

--Corrected a few palpable typos.

--Included a transcription of the text within some images.

--In the text versions only, text in italics is delimited by
  _underscores_.