A New Subspecies of Ground Squirrel (Spermophilus spilosoma) from Tamaulipas, Mexico

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  UNIVERSITY OF KANSAS PUBLICATIONS
  MUSEUM OF NATURAL HISTORY

  Volume 14, No. 8, pp. 121-124
  March 7, 1962

  A New Subspecies of Ground Squirrel
  (Spermophilus spilosoma) from Tamaulipas,
  Mexico

  BY

  TICUL ALVAREZ

  UNIVERSITY OF KANSAS
  LAWRENCE
  1962




  UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

  Editors: E. Raymond Hall, Chairman, Henry S. Fitch,
  Theodore H. Eaton, Jr.

  =Volume 14, No. 8, pp. 121-124
  Published March 7, 1962=

  UNIVERSITY OF KANSAS
  Lawrence, Kansas

  PRINTED BY
  JEAN M. NEIBARGER, STATE PRINTER
  TOPEKA, KANSAS
  1962


  29-1505




A New Subspecies of Ground Squirrel (Spermophilus spilosoma) from
Tamaulipas, Mexico

BY TICUL ALVAREZ


When A. H. Howell (N. Amer. Fauna, 56:1-256, 1938) revised the North
American ground squirrels, he had no specimens of the spotted ground
squirrel, _Spermophilus spilosoma_, from Tamaulipas. Thirteen years
later, Hall (Univ. Kansas Publ., Mus. Nat. Hist., 5:38, 1951) listed the
species for the first time from the state when he recorded as _S. s.
annectens_ 13 specimens from the barrier beach 88-89 miles south and 10
miles west of Matamoros.

In 1953, Mr. Gerd Heinrich collected 10 individuals of _S. spilosoma_
from the coastal plain of eastern Tamaulipas that extend southward the
known range of the species on the east coast of Mexico, provide the
first specimens from the mainland of Tamaulipas, and represent a new
subspecies that is named and described below.


=Spermophilus spilosoma oricolus= new subspecies

     _Type._--Female, adult, skin and skull, No. 55497 Museum of Natural
     History, The University of Kansas; from one mile east of La Pesca,
     Tamaulipas, Mexico; obtained on May 27, 1953, by Gerd Heinrich,
     original number 6933.

     _Diagnosis._--Size medium for species (see measurements); general
     color cinnamon buff, almost pure on dorsal surface of hind foot and
     dorsal and ventral midline of tail; spots well marked; postorbital
     constriction narrow; auditory bullae small; viewed from front,
     lower border of maxillary plate forming continuously concave line
     with jugal; zygomatic process of maxillary narrow, having anterior
     border concave.

     _Comparisons._--From _Spermophilus spilosoma annectens_ (specimens
     from Padre and Mustang islands, Texas), _S. s. oricolus_ differs as
     follows: larger in external dimensions but smaller in cranial
     dimensions; postorbital constriction narrower, 13.4 (13.2-13.8)
     instead of 14.0 (13.5-14.7); rostrum slightly broader; greatest
     distance between posterior border of maxillary plate and squamosal
     arm of zygoma longer, averaging 9.9 (9.7-10.2) instead of 9.6
     (9.0-10.1); zygomatic process of maxillary, viewed dorsolaterally
     above lacrimal narrower, having anterior border concave instead of
     almost straight; when skull viewed from front, lower border of
     maxillary plate forming continuously concave line with jugal
     instead of almost a right angle where jugal and maxillary meet;
     ramus of lower jaw narrower; general color paler; upper surface of
     hind foot washed with cinnamon instead of yellowish; postauricular
     spot absent (usually present in _annectens_).

     From _Spermophilus spilosoma pallescens_ (specimens from
     southeastern Coahuila), _S. s. oricolus_ differs as follows: color
     more cinnamon especially on upper surface of hind foot; dorsal
     spots more distinct; smaller externally, except hind foot, which
     measures the same; braincase and postorbital constriction narrower;
     nasals shorter; auditory bullae conspicuously smaller.

     From _Spermophilus spilosoma cabrerai_ (specimens from eastern San
     Luis Potosi), _S. s. oricolus_ differs mainly in pale (cinnamon)
     rather than dark (blackish) upper parts, but differs also in being
     smaller externally (judging from measurements given in the original
     description by Dalquest, Proc. Biol. Soc. Washington, 64:107,
     1951), and in having a greater zygomatic breadth, narrower
     braincase and postorbital constriction, and narrower maxillary
     process.

     _Measurements._--Average and extreme measurements of eight
     specimens from the type locality (four females, including type, and
     four males) are as follows: total length (only five specimens), 234
     (212-245); length of tail vertebrae (five only), 67 (50-75); length
     of hind foot, 36.1 (35-37); length of ear from notch, 8.4
     (7.5-10.0); length of head and body, 166 (155-171); greatest length
     of skull, 41.2 (40.6-42.7); zygomatic breadth, 24.4 (23.7-25.2);
     cranial breadth, 18.4 (17.8-18.9); interorbital constriction, 9.2
     (8.5-9.8); postorbital constriction, 13.4 (13.2-13.8); length of
     nasals, 14.0 (13.6-14.8); length of maxillary tooth-row, 8.0
     (7.7-8.4); greatest distance between posterior border of maxillary
     plate and squamosal arm of zygoma, 9.9 (9.7-10.2).

     _Remarks._--The type locality of _S. s. oricolus_ is nearly at sea
     level on the coastal plain of eastern Tamaulipas. In so far as now
     known, the population of ground squirrel here named as new is
     isolated, the nearest records of occurrence being those reported by
     Hall (_loc. cit._) from a place on the barrier beach approximately
     80 miles north of La Pesca. The nearest record from the mainland
     (_S. s. annectens_) is from southern Texas.

     A possible explanation for the presence of the species at La Pesca
     is that it dispersed southward along the barrier beach, and that an
     isolated or semi-isolated segment finally reached the mainland
     where the barrier beach rejoins it just northeast of La Pesca. This
     possibility is strengthened by study of the specimens already
     mentioned from 88-89 miles south and 10 miles west of Matamoros,
     because they combine many characters of _annectens_ and _oricolus_.
     The insular specimens differ from both _annectens_ and _oricolus_
     in having shorter nasals and a shorter skull, narrower zygomatic
     and interorbital regions, and a relatively broader interpterygoid
     space. Also, the zygomatic process of the maxillary, viewed
     dorsolaterally above the lacrimal, is even narrower that in
     _oricolus_ and has the anterior border even more concave. In color,
     specimens from the barrier beach are pale as is _oricolus_, but the
     over-all color is reddish cinnamon rather than cinnamon buff.
     Concerning the juncture of the zygomatic plate with the jugal, 12
     of the 13 specimens studied resemble _annectens_ in this character
     and one resembles _oricolus_. The specimens from the barrier beach
     may themselves represent an unnamed subspecies; more material than
     now is available is needed, because most of the specimens are not
     fully adult. Because the 13 specimens from the barrier beach
     resemble _oricolus_ slightly more than _annectens_, all characters
     considered, they are tentatively assigned to _oricolus_.

     The author is grateful to Professor E. Raymond Hall and Mr. J. Knox
     Jones, Jr., for permission to examine the specimens here reported
     and for helpful suggestions. Field work that yielded the specimens
     was financed by the Kansas University Endowment Association. The
     laboratory phases of the study were made when the author was a
     half-time Research Assistant supported by a grant, No. 56 G 103,
     from the National Science Foundation.

     _Specimens examined._--A total of 23, all from Tamaulipas: 88 mi.
     S, 10 mi. W Matamoros, 12; 89 mi. S, 10 mi. W Matamoros, 1; 1 mi. E
     La Pesca, 10.

_Transmitted November 8, 1961._


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