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A New Piñon Mouse (Peromyscus truei) from
Durango, Mexico

BY

ROBERT B. FINLEY, JR.




University of Kansas Publications
Museum of Natural History

Volume 5, No. 20, pp. 263-267
May 23, 1952




University of Kansas
LAWRENCE
1952




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. 20, pp. 263-267
May 23, 1952




UNIVERSITY OF KANSAS
Lawrence, Kansas




PRINTED BY
FERD VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS
1952

24-2794




A New Piñon Mouse (Peromyscus truei) from
Durango, Mexico

BY

ROBERT B. FINLEY, JR.


The extensive collection of Mexican mammals made by Mr. J. R.
Alcorn for the University of Kansas Museum of Natural History
contains fourteen piñon mice from lava rocks eight miles northeast
of the city of Durango, Mexico. These mice are all much darker
than the piñon mice, _Peromyscus truei gentilis_, of adjoining areas
in Durango and Zacatecas and show a superficial resemblance to
the widespread _P. t. gratus_ which occurs 450 miles to the southeast.
Morphological differences from _P. t. gratus_, as well as geographic
considerations (see remarks), make desirable the recognition of the
lava-dwelling piñon mice from Durango as a distinct subspecies.

All specimens examined of subspecies compared with the series
of piñon mice from northeast of Durango are in the University of
Kansas Museum of Natural History. Capitalized color names and
designators are of Maerz and Paul, A Dictionary of Color, McGraw
Hill Book Co., New York, 1930.

I wish to acknowledge generous financial aid from the Kansas
University Endowment Association which made possible the field
work by Mr. Alcorn in Mexico.

This heretofore unknown subspecies is characterized below and
may be known as:

=Peromyscus truei erasmus= subsp. nov.

_Type._--Mus. Nat. Hist., Univ. Kansas, no. 34417, young adult female, skin
and skull; from eight miles northeast of Durango, 6200 feet, Durango,
Mexico; collected 16 August 1949 by J. R. Alcorn, original number 10255.

_Range._--Known only from the type locality.

_Diagnosis._--Upper parts dark brownish gray (Smoke Brown, 16 A 2, to
Biskra, 16 A 12), darkest between ears; lower sides suffused with dull
orange buff (13 H 9 to 12 H 9); dark eye ring and black spot at base of
vibrissae conspicuous; ears 95 to 100 per cent as long as hind foot; bullae
round, greatly inflated; interparietal large, anterior margin curved or
slightly sinuous, not bulging strongly forward laterally; rostrum short;
nasals broad; braincase high and full; incisive foramina slightly pointed
anteriorly; molars small, as in _P. t. gentilis_.

_Measurements._--Measurements of 3 males and mean and extreme measurements
of 11 females, all from the type locality, are, respectively, as follows:
total length, 192, 188 (incomplete), 196 (incomplete), 193 (188-209);
length of tail, 102, 97 (broken), 97 (broken), 101 (94-114); length of hind
foot, 22, 23, 23, 22.5 (22-23); length of ear, from notch, in flesh, 21,
22, 23, 21.5 (20-23); greatest length of skull, 27.4, 27.7, 27.9, 27.3
(26.5-28.3); basilar length, 20.2, 21.0, -- (broken), 20.4 (19.6-21.2);
greatest breadth of braincase, 12.8, 12.8, 13.3, 12.85 (12.4-13.4); least
interorbital breadth, 4.4, 4.6, 4.6, 4.41 (4.2-4.6); length of nasals,
10.1, 10.3, 10.9, 10.3 (9.8-11.1); diastema, 6.6, 7.0, 7.1, 6.78 (6.3-7.2);
length of incisive foramina, 5.6, 5.9, 6.0, 5.77 (5.5-6.0); length of
palatal bridge, 3.8, 3.9, --, 3.96 (3.8-4.3); postpalatal length, 9.9, --,
--, 9.7 (9.2-10.4); alveolar length of maxillary tooth-row, 4.1, 4.1, 4.4,
4.2 (4.1-4.4). All measurements are in millimeters.

_Measurements of the type._--Total length, 189; length of tail, 95; length
of hind foot, 22; length of ear, from notch (in flesh), 21; greatest length
of skull, 26.9; basilar length, 20.3; greatest breadth of braincase, 13.0;
least interorbital breadth, 4.4; length of nasals, 10.1; diastema, 6.6;
length of incisive foramina, 5.5; length of palatal bridge, 3.9;
postpalatal length, 9.8; alveolar length of maxillary tooth-row, 4.2.

_Comparisons._--From _Peromyscus truei gentilis_ (specimens from 5 mi. N
Durango, Durango; 4 mi. W Durango, Durango; and 8 mi. N & 1 mi. W
Sombrerete, Zacatecas), the subspecies of the surrounding region, _P. t.
erasmus_ differs in markedly darker coloration, sides and face less
brightly washed with orange buff, dark eye ring and spot at base of
vibrissae more conspicuous, higher incidence and greater extent of buffy
pectoral spot. External measurements do not differ significantly. No
consistent cranial differences were found.

From _Peromyscus truei gratus_ (specimens from Pedregal de los Reyes,
Distrito Federal, México) to the southeast, _P. t. erasmus_ differs in
slightly darker dorsal color, more inflated bullae, and less sinuous (not
bulging so much forward laterally) anterior margin of interparietal.

From _Peromyscus truei gratus_ (specimens from various localities in
eastern Jalisco and western Michoacán) to the south, _P. t. erasmus_
differs in slightly darker dorsal color, longer ears, and more inflated
bullae.

From _Peromyscus truei truei_ (specimens from 4 mi. N El Rito, Rio Arriba
Co., New Mexico) to the northwest, _P. t. erasmus_ differs in much darker
color, shorter tail, shorter hairs on tail, smaller ears, shorter rostrum,
wider nasals, and more pointed anterior ends of incisive foramina.

_Remarks._--The tail of _P. t. erasmus_ varies greatly in color, being
either bicolor or unicolor, dark gray above and varying from white
to dark gray below. The type has the tail dark gray above grading
gradually on the sides to medium gray below. A buffy pectoral
spot or band is present in about half of the adults examined, being
most prominent in the type, which is also one of the darkest specimens
in the series. The shape of the posterior edge of the bony
palate is also variable, being convex, square, or concave; and the
dorsal branches of the premaxillaries may terminate slightly anterior
or slightly posterior to the posterior ends of the nasals. In the type
the posterior palatal margin is concave and the dorsal branches of
the premaxillaries almost reach the ends of the nasals. _Peromyscus
truei gratus_ from Distrito Federal also shows high variability in all
these characters.

_Peromyscus truei erasmus_ is a dark race of the piñon mouse known
from the west side of a rough area of dark lavas a few miles northeast
of the city of Durango and closely surrounded by the light colored
race, _P. t. gentilis_, known from outside the area of lava rocks.
Specimens of _erasmus_ from eight miles northeast of Durango are
all conspicuously darker than 11 specimens of _gentilis_ from five
miles north of Durango and four miles west of Durango which are
typical in color for _gentilis_. Although _erasmus_ more nearly resembles
in color _gratus_, in cranial characters and external measurements
it shows closer relationship to _gentilis_.

Alcorn reported (verbal communication) that the type series of
_erasmus_ was collected on the west side of the Río de la Saucida in
hills covered with broken lava rocks, cactus, and spiny shrubs.
Some cottonwoods grow along the river, which is almost dry most
of the time. East of the river is a flat plain or valley of adobelike
soil a few miles wide beyond which extends a rough area of dark
lavas. The approximate extent of the lava plain is indicated on
World Aeronautical Chart, Lake Santiaguillo (521). The specimens
of _gentilis_ from five miles north of Durango and four miles west of
Durango were collected on slopes of adobe soil covered with grasses,
scattered junipers and low shrubs, this habitat being the lower eastern
edge of the juniper-wooded slopes that rise westward to the
Sierra Madre Occidental.

The available facts suggest that _P. t. erasmus_ has evolved from
_P. t. gentilis_ by natural selection for concealing coloration on the
dark lavas northeast of Durango, México. _P. t. erasmus_ probably
reaches its western limit close to the type locality.

_Specimens examined._--Total 14, from the type locality.

_Museum of Natural History, University of Kansas, Lawrence._

_Transmitted January 21, 1952._

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