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Comments on
the Taxonomy and Geographic Distribution
of Some North American Rabbits

BY

E. RAYMOND HALL and KEITH R. KELSON

University of Kansas Publications
Museum of Natural History
Volume 5, No. 5, pp. 49-58
October 1, 1951

University of Kansas
LAWRENCE
1951


UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

Editors: E. Raymond Hall, Chairman, A. Byron Leonard,
Edward H. Taylor, Robert W. Wilson

Volume 5, No. 5, pp. 49-58
October 1, 1951

UNIVERSITY OF KANSAS
Lawrence, Kansas

PRINTED BY
FERD VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS
1951
[Illustration]
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Comments on the Taxonomy and Geographic Distribution of Some North
American Rabbits

BY

E. RAYMOND HALL AND KEITH R. KELSON


In preparing maps showing the geographic distribution of North American
lagomorphs, some conflicting statements in the literature have led us to
examine the pertinent specimens of the Florida cottontail and the
Audubon cottontail with results as given below. The study here reported
upon was aided by a contract between the Office of Naval Research,
Department of the Navy, and the University of Kansas (NR 161-791).
Unless otherwise indicated, catalogue numbers are of the United States
National Museum and most of the specimens are in the Biological Surveys
collection of the Fish and Wildlife Service. Grateful acknowledgment is
made to persons in charge of the collections for permission to use the
collections under their charge.


Sylvilagus floridanus similis Nelson

     1907. _Sylvilagus floridanus similis_ Nelson, Proc. Biol. Soc.
     Washington, 20:82, July 22.

Some confusion has existed concerning the subspecific identity of the
Florida cottontail in Nebraska because of the way in which Nelson
recorded specimens in his "The Rabbits of North America" (N. Amer.
Fauna, 29:fig. 11, and pp. 169-174, August 31, 1909). He (_op.
cit._:174) listed the following specimens under the western subspecies,
_S. f. similis_: Two topotypes (Nos. 87784 and 18738/25532) and of
course the type; the specimen (No. 116288) from the Snake River [= Snake
Creek of maps], 11 mi. NW Kennedy; two from Neligh (126074 and 151438);
and one (probably 18680/25410) from Kennedy. But, he listed (_op.
cit._:172) under _S. f. mearnsi_, the eastern subspecies, a specimen
(10721) from Brownlee, and two from Kennedy. One of the two from Kennedy
probably was the one that is recorded in the files of the U.S. Fish and
Wildlife Service as "identified by Cary. spec. in Univ. Nebraska". The
other, or third, specimen from Kennedy, we judge, did not exist at all
but was recorded by Nelson because a card in the reference file, under
Kennedy, Nebraska, in addition to No. 18680/25410, carried a second
entry, a number 3471X. The latter is the X-catalogue number of specimen
No. 116288 from the Snake River! The X-catalogue is used in place of a
field catalogue for specimens sent to the mammal collection of the
United States Fish and Wildlife Service, by persons who do not keep
regular field numbers of their own. It seems that Nelson prepared (or
had prepared) his lists of specimens, at least in part, from cards
rather than from the labels on the specimens themselves. Some further
confusion as to names that Nelson intended to apply to cottontails in
Nebraska resulted from the fact that his map (_op. cit._:fig. 11)
indicated that the localities mentioned above for _S. f. mearnsi_ were
within the geographic range of _S. f. similis_.

Our comparison of each of the Nebraskan specimens with specimens of _S.
f. mearnsi_ in comparable pelage from Iowa and with the type and
topotypes of _S. f. similis_ reveals that each of the specimens of which
catalogue numbers are given above is clearly referable to _Sylvilagus
floridanus similis_.

Because some mammalogists have suspected that intergradation between
_Sylvilagus floridanus similis_ and _Sylvilagus nuttallii grangeri_
occurs along the eastern base of the Rocky Mountains, we have examined
specimens which may throw light on this matter.

From _S. f. similis_ (holotype and three topotypes), _S. n. grangeri_
(eight practical topotypes from Redfern, South Dakota) differ as
follows: Throat patch darker; hind foot shorter; ear (dry) from notch
longer; rostrum narrower; posterior extension of supraorbital process
enclosing a longer and wider space between it and the braincase;
superior border of premaxilla straight in profile instead of convex
dorsally; tympanic bullae more inflated; external auditory meatus larger
(diameter of the meatus more, instead of less, than crown length of
upper molars); posterior border of palate without, instead of with,
spine.

Specimens of the two species from places as near each other as extreme
southeastern Montana (_S. f. similis_ from Boxelder Creek, Capitol and
the Little Missouri River) and Devils Tower, Wyoming (_S. n. grangeri_),
seem not to differ in the length of the hind foot and the ear and in the
color of the spot on the chest. Also, the presence or absence of the
spine on the posterior margin of the palate is subject to individual
variation in these specimens but the other cranial differences,
mentioned above, still are apparent. These same cranial differences are
readily apparent between specimens of the two species taken only five
miles apart in eastern Wyoming (for the precise localities, see the
following paragraph). It is concluded, therefore, that _S. f. similis_
and _S. n. grangeri_ do not inter-grade along the eastern base of the
Rocky Mountains.

Data on specimens from Laramie County in eastern Wyoming show that _S.
f. similis_ is a heavier animal than _S. n. grangeri_ and also that
_similis_ molts earlier. For example, an adult female (K.U. No. 15936)
taken on July 13, 1945, three miles east of Horse Creek P.O., 6400 ft.,
weighed 1374 grams and is in fresh pelage, whereas an adult female of
_S. n. grangeri_ (K.U. No. 15935), taken on July 17, 1945, two miles
west of Horse Creek P.O., 6600 ft., weighed only 1149 grams, and still
has some of the worn winter pelage on the upper parts.


Sylvilagus floridanus holzneri (Mearns)

     1896. _Lepus sylvaticus holzneri_ Mearns, Proc. U.S. Nat. Mus.,
     18:554, June 24.

     1904. _Sylvilagus floridanus holzneri_, Lyon, Smithsonian Miscl.
     Coll., 45:336, June 15.

Examination of cottontail rabbits from Arizona in the Biological Surveys
Collection and the United States National Museum indicates that
_Sylvilagus audubonii_ can be distinguished from _Sylvilagus nuttallii_
and _Sylvilagus floridanus_ by the larger (more inflated) tympanic
bullae. Topotypes of _Sylvilagus nuttallii pinetis_ and other specimens
from Alpine, Mt. Thomas, Springerville, the Prieto Plateau at 9000 feet
on the south end of the Blue Range, and the Tunitcha Mountains are
characterized by a posteriorly pointed supraoccipital shield and a long,
wide space between the braincase and the posterior extension of the
supraorbital process. The cottontails with equally small tympanic bullae
from more western and more southern localities are referable to
_Sylvilagus floridanus holzneri_ on the basis of a posteriorly truncate
or emarginate supraoccipital shield and a narrower and shorter space
(usually a "foramen") between the braincase and the posterior extension
of the supraorbital process. In _S. f. holzneri_ the posterior end of
the posterior process fuses with the braincase whereas the posterior end
of this process in Arizonan specimens of _S. n. pinetis_ merely lies
against the braincase or projects free of it. In specimens from Arizona
the difference in shape of the posterior border of the supraoccipital
shield and the difference in size of the space between the braincase and
the posterior extension of the supraorbital process are the only
differences of taxonomic worth found by us. Many other features of the
skull, of color of pelage, and of size of external parts all fell within
the range of individual variation of a series of specimens from one
locality.

Specimens from the following localities in Arizona are referable to
_Sylvilagus floridanus holzneri_ (Mearns).

     Hualpai Mts., Nos. 117461, 117462, 117488, 117490, 117495, 227735,
     and 227832; Ft. Whipple, No. 214157; Prescott, No. 34667/46752;
     Mayer, No. 247495; Reynolds Creek Ranger Station, Sierra Ancha
     Mts., Gila Co., No. 247734; Fish Creek, Tonto National Forest, 2000
     ft., No. 212833; north base Mt. Turnbull, 4500 ft., No. 214339; Ash
     Creek, 6100 ft., Graham Mts., No. 204363; Pinery Canyon, 7500 ft.,
     Chiricahua Mts., No. 247953; Thomas Cañon, 2 mi. E Baboquivari
     Mts., No. 244420; Pine Springs, 15 mi. south of Colorado Cañon, No.
     2425 Amer. Mus. Nat. Hist. On December 4, 1950, we removed the
     skull of No. 2425 to more certainly ascertain the identity of the
     individual.

The specimens listed above include those that Nelson (N. Amer. Fauna,
29:211, August 31, 1909) listed from the Hualpai Mountains, Pine
Springs, and Prescott under the name _Sylvilagus nuttallii pinetis_.
Nelson (_op. cit._:Pl. X, fig. 2) figured one of these skulls from the
Hualpai Mountains as _S. n. pinetis_ and the cranial measurements (_op.
cit._:201) that he records for _S. nuttallii pinetis_ likewise are of
these same specimens of _Sylvilagus floridanus holzneri_. Nelson's
description (_op. cit._:207-210) seems to have been affected by the
erroneous (as we see the matter) inclusion of these specimens of _S. f.
holzneri_ in the materials identified by him as _Sylvilagus nuttallii
pinetis_.

The specimens so far mentioned from Arizona can be identified with ease.
The identification becomes difficult, however, when the holotype of _S.
f. holzneri_, from the Huachuca Mountains, is examined. The difficulty
results from the holotype having a barely detectable emargination in the
posterior border of the supraoccipital shield. In this respect the
holotype is intermediate between _S. f. holzneri_ (as known by specimens
from more western localities in Arizona) and _S. n. pinetis_ from the
White Mountains to the northward. As noted above, _S. f. holzneri_ has a
deep notch and _S. n. pinetis_ has none. This intermediacy of the
holotype supports the possibility, mentioned by Nelson (_op. cit._:200),
that intergradation occurs between _S. f. holzneri_ and _S. n. pinetis_.
Additional evidence, however, is against this possibility; the notch in
the supraoccipital is deeper in specimens (No. 66136, from Chiricahua
Mts., and No. 204364, from Ash Creek in Graham Mts.) from mountains
geographically intermediate between the Huachuca Mountains and the White
Mountains. Also, the holotype of _S. f. holzneri_ differs from _S. n.
pinetis_ and agrees with other specimens of _S. f. holzneri_ from
farther southwest in Arizona in the robustness of the posterior
extensions of the supraorbital processes and in the considerable degree
of fusion of the tips of these processes with the squamosals.
Additionally, the rostrum of the holotype is wide and deep as in other
specimens of _S. floridanus_ from more eastern localities and is unlike
the narrow and shallow rostrum of _S. n. pinetis_.

If intergradation occurs in Arizona between the species _Sylvilagus
floridanus_ and _Sylvilagus nuttallii_, as Nelson (_op. cit._:200)
intimated it might, the intergrades probably will be found along the
Tonto Rim or in the territory between the Blue Range and the Graham
Mountains.


Sylvilagus floridanus cognatus Nelson

     1907. _Sylvilagus cognatus_ Nelson, Proc. Biol. Soc. Washington,
     20:82, July 22.

We have examined the specimens recorded by Nelson (N. Amer. Fauna,
29:193, August 31, 1909) and conclude that Nelson (_op. cit._)
accurately described them. We differ from Nelson on one point of
interpretation; we prefer to use the trinomial, instead of the binomial,
for _cognatus_ because the kind and amount of difference between it and
subspecies of _Sylvilagus floridanus_ (_S. f. holzneri_ and possibly _S.
f. llanensis_) is on the order of magnitude that distinguishes
subspecies, and not full species, of _Sylvilagus_.

The specimen (W.D. Hollister, original No. 208) from the Datil
Mountains, lent to us by the Colorado Museum of Natural History, does
have, as Nelson (_op. cit._) pointed out, larger tympanic bullae and a
slenderer rostrum than do other specimens of _S. f. cognatus_.
Nevertheless, No. 208, agrees with _cognatus_ and differs from
_Sylvilagus nuttallii pinetis_ in the greater vertical depth of the
zygoma, the greater transverse width of the first pair of upper
incisors, the broader posterior extensions of the supraorbital
processes, the fusion (instead of freedom from, or mere touching to, the
braincase) of the tips of these extensions, the less upturned
supraorbital processes, and the more nearly truncate posterior margin of
the supraorbital shield. Therefore, the specimen is referable to
_Sylvilagus floridanus cognatus_. The slender rostrum and large tympanic
bullae of No. 208 are either individual variations or features peculiar
to the population of _Sylvilagus floridanus_ in the Datil Mountains.


Sylvilagus floridanus robustus Bailey

     1905. _Lepus pinetis robustus_ V. Bailey, N. Amer. Fauna, 25:159,
     October 24.

Nelson (N. Amer. Fauna, 29:194-195, August 31, 1909) described specimens
from the Big Bend area of Texas. This was the only area from which
Nelson had specimens. Our examination of these same specimens indicates
that his description of them was accurate. Davis and Robertson (Jour.
Mamm., 25:271, September 8, 1944) recorded a specimen, under the name
_Sylvilagus robustus_, from "The Bowl, Guadalupe Mountains, Culberson
County, Texas." Our examination of the skull of this specimen
([female] adult, No. 658, Mus. Zool., Louisiana State
University) indicates that it is, among named kinds of rabbits, best
referred to _robustus_. The specimen is morphologically as well as
geographically intermediate between _S. f. cognatus_ and _S. robustus_.
This morphological intermediacy is illustrated by certain of the
following cranial measurements of three adult females: No. 108695
(_robustus_), Chisos Mts.; No. 658 from the Guadalupe Mts.; and No.
128651, NE slope Capitan Mts. Basilar length, 59.2, 54.2, 54.4; length
of nasals, 33.9, 31.1, 32.2; breadth of rostrum above premolars, 19.3,
17.5, 17.0; depth of rostrum in front of premolars, 15.8, 14.8, 14.0;
interorbital breadth, 20.4, 19.1, 19.7; parietal breadth, 27.2, 27.1,
26.5; diameter of bulla, 13.3, 12.2, 10.7. Considering the intermediate
nature of specimen No. 648, and the kind and amount of difference
between _Sylvilagus floridanus cognatus_ and _S. robustus_, it seems
appropriate to us to use the name-combination _Sylvilagus floridanus
robustus_.

Actual intergradation, in the sense of interbreeding between individuals
of a continuously distributed population of animals, probably does not
occur regularly between _S. f. cognatus_ and _S. f. robustus_ nor
between several populations within either one of these subspecies; in
south-central Arizona and western Texas the animals are said to occur
only in the higher parts of the mountains. Consequently a given
population is separated from another by low-lying territory inhospitable
to the species _Sylvilagus floridanus_. This low-lying territory is
inhabited by another species, _Sylvilagus audubonii_. More intensive
collecting in the region concerned may, however, show a continuous
distribution of the species _Sylvilagus floridanus_ in several areas
where it seems now to have an interrupted distribution.


Sylvilagus audubonii neomexicanus Nelson

     1907. _Sylvilagus audubonii neomexicanus_ Nelson, Proc. Biol. Soc.
     Washington, 20:83, July 22.

Nelson (N. Amer. Fauna, 29:230, August 31, 1909) listed under
_Sylvilagus audubonii cedrophilus_ Nelson an adult female, skin with
skull (U.S. Nat. Mus., Biol. Surv. Coll., No. 108698) from fifteen miles
south of Alpine, Texas. Nelson (_loc. cit._) remarked that the
"bleached" color of the back and the great lateral breadth of the
tympanic bullae of No. 108698 were peculiarities not possessed by any
other specimen examined. Geographically, the locality of capture is far
south of other known occurrences of _S. a. cedrophilus_ and
approximately on the boundary separating the range of _S. a. minor_ from
that of _S. a. neomexicanus_. The large size, which may have induced
Nelson to refer the specimen to _S. a. cedrophilus_, is not surprising
considering that the individual is a female and fully adult. A
combination of new and old fur on the upper parts presents a pattern
that might be duplicated in other specimens of _S. a. neomexicanus_. The
lateral inflation of the tympanic bullae can be interpreted as
intergradation with the geographically adjacent _S. a. minor_ to the
south; _S. a. minor_ has large bullae. There are no features otherwise
which suggest that the specimen is anything other than _Sylvilagus
audubonii neomexicanus_ and we refer it to that subspecies.


Sylvilagus audubonii minor Mearns

     1896. _Lepus arizonae minor_ Mearns, Proc. U.S. Nat. Mus., 18:557,
     June 24.

     1907. _S[ylvilagus]. a[uduboni]. minor_, Nelson, Proc. Biol. Soc.
     Washington, 20:83, July 22.

Nelson (N. Amer. Fauna, 29:230, August 31, 1909) listed, without
comment, under _Sylvilagus audubonii cedrophilus_ Nelson, a skin with
skull inside (Amer. Mus. Nat. Hist., 5419, [female] adult or sub-adult)
from San Diego, Chihuahua, Mexico. We locate San Diego approximately 230
miles south and 60 miles east of El Paso, Texas. Thus, the specimen is
from near the center of the geographic range of _Sylvilagus audubonii
minor_. With the permission of Mr. G.G. Goodwin of the American Museum
of Natural History we removed the skull. It differs in no essential
features from those of other specimens of _S. a. minor_. For example, of
specimens in the United States National Museum, Biological Surveys
Collection, a female (No. 132002) from Guzman in Chihuahua, and a male
(No. 51020) from Santa Rosalia in the same state, are almost
indistinguishable from the San Diegan specimen. The specimen is without
external measurements but the length of the hind foot and length of ear
from the notch in the dry state (80 and 57, respectively) agree with the
corresponding measurements of _S. a. minor_. Color of the skin furnishes
no diagnostic character as between _S. a. minor_ and _S. a.
cedrophilus_. We identify the specimen from San Diego as _Sylvilagus
audubonii minor_.

_Transmitted January 30, 1951._


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