Figs. 1-3. Three views of the skull of the type specimen of Thomomys
umbrinus pullus. × 1.
Title: A New Pocket Gopher (Thomomys) and A New Spiny Pocket Mouse (Liomys) from Michoacán, Mexico
Author: E. Raymond Hall
Bernardo Villa Ramírez
Release date: November 14, 2010 [eBook #34314]
Language: English
Credits: Produced by Chris Curnow, Joseph Cooper and the Online
Distributed Proofreading Team at http://www.pgdp.net
A series of 17 pocket gophers of the species Thomomys umbrinus obtained in 1943 from points 3, 4 and 5 miles south of Pátzcuaro proves upon comparison to be an hitherto unrecognized subspecies which is described and named as follows:
Thomomys umbrinus pullus, new subspecies
Type.—Male, adult, skin and skull; No. 100151, Univ. California Mus. Vert. Zool.; 5 mi. S Pátzcuaro, 7800 ft., Michoacán, Mexico; March 10, 1943; obtained by Hubert H. Hall, original No. 117.
Range.—Known only from 3 to 5 miles south of Pátzcuaro, Michoacán.
Diagnosis.—Size small (see measurements); color black or between Cinnamon-Brown and Snuff Brown; distal half of tail whitish and all of tail whitish in one specimen; lambdoidal crests perpendicular to sagittal plane of skull; posteroventral face of tympanic bulla rugose; jugal vertical (flat surface not oblique); interpterygoid space truncate at apex with sides curved outward (see figure).
Comparison.—From topotypes of Thomomys umbrinus supernus Nelson and Goldman, pullus differs as follows: More individuals wholly black (except distal half of tail); underparts lacking white; rostrum broader; braincase anteriorly slightly more expanded dorsally; lambdoidal crests perpendicular to sagittal plane rather than inclined posteromediad; interparietal broader, ♂ 5.7 (5.0-7.0) versus 4.5, and in ♀ 6.5 (5.6-7.1) rather than 4.8 (4.4-5.1); flattened middle part of jugal vertical rather than oblique; in side view, mastoid and paroccipital processes farther apart thus exposing larger surface of mastoidal bulla; incisors, in both upper and lower jaws, slightly narrower; molariform teeth smaller, interpterygoid space truncate, at apex, with sides convex mediad, rather than V-shaped; ventral face of tympanic bullae rugose in posterior half rather than smooth.
Figs. 1-3. Three views of the skull of the type specimen of Thomomys
umbrinus pullus. × 1.
Remarks.—Among named subspecies of Thomomys umbrinus, T. u. pullus most closely resembles T. u. supernus, the subspecies next adjacent to the northward. Therefore, the results of comparisons with only that subspecies are here reported upon. T. u. tolucae to the eastward is for one thing a much larger animal and has slightly less procumbent upper incisors. So far as we know, Thomomys umbrinus has not heretofore been reported from Michoacán. Of our seventeen skins, eight are brown, six are black and two are intermediate in color.
Most of these pocket gophers lived where there was a good growth of pine trees in the same areas where large pocket gophers of the species Cratogeomys gymnurus occurred. The field notes of the collector of the type of T. u. pullus record that when he was making a shallow excavation to reveal the gopher burrow in which he trapped the holotype, he found the burrow approximately five inches below the surface of the ground and that in digging deeper than was necessary he accidentally broke into the burrow of a Cratogeomys. Another member of our field party (E. R. Hall) when removing from its burrow a trapped Thomomys that was caught only by the hind leg, dug around the animal whose burrow was approximately six inches underground and in doing so he also broke through the roof of a burrow of Cratogeomys. The burrow of Cratogeomys was approximately sixteen inches below the ground. Nowhere else, except 3 to 5 miles south of Pátzcuaro, have the authors found two kinds of pocket gophers living together. The two-story arrangement south of Pátzcuaro was possible because of the different levels at which the two kinds of animals made their burrows and the two-story arrangement was accidental and exceptional rather than the rule.
Measurements.—Average and extreme measurements of five adults of each sex, are as follows: Total length, male 184 (178-198), female 185 (174-194); length of tail, 54 (48-60), 53 (47-57); length of hind foot, 26.8 (25-29), 27.6 (26-29); weight, 86.1 (78.7-96.9), 74.3 (70.2-84.8) grams; basilar length, 30.2 (28.8-31.3), 28.6 (27.8-29.1); zygomatic breadth, 23.2 (22.3-24.6), 21.3 (20.8-21.8); least interorbital breadth, 5.9 (5.8-6.1), 6.4 (6.0-6.8); mastoid breadth, 17.8 (17.1-18.7), 17.2 (16.6-17.5); length of nasals, 12.4 (11.8-13.0), 11.5 (11.0-12.5); breadth of rostrum, 7.5 (6.9-8.2), 7.1 (6.9-7.3); length of rostrum, 14.1 (13.4-14.5), 13.3 (12.7-13.5); alveolar length of maxillary tooth-row, 7.0 (6.7-7.5), 6.9 (6.8-7.0); palato-frontal depth, 13.2 (13.0-13.4), 12.9 (12.3-13.5).
Specimens examined.—Total, 17, all from 7800 ft., Michoacán, as follows: 3 mi. S Pátzcuaro, 1; 4 mi. S Pátzcuaro, 10; 5 mi. S Pátzcuaro, 6.
In 1943 a series of fifteen spiny pocket mice, Liomys irroratus, was obtained within a radius of five miles of Pátzcuaro and, mostly on geographic considerations, the animals were assigned to Liomys irroratus alleni (Coues). In fact, in his "Revision of the Spiny Pocket Mice," Goldman (N. Amer. Fauna, 34:57, 1911) had thus identified the one specimen available to him from Pátzcuaro. Critical examination of the series, however, revealed cranial features not described in the named kinds from adjoining geographic areas, and comparisons showed that the animal from Pátzcuaro differs subspecifically from any named kind. The new subspecies may be known as:
Liomys irroratus acutus, new subspecies
Type.—Female, adult, skin and skull; No. 100171, Univ. California Mus. Vert. Zool.; 2 mi. W. Pátzcuaro, 7700 ft., Michoacán, Mexico; March 10, 1943; obtained by E. R. Hall and J. R. Alcorn, original No. 3837 of Alcorn.
Range.—Known only from the vicinity of Pátzcuaro, Michoacán.
Diagnosis.—Size large (see measurements); upper parts dark brown; posterior border of nasals V-shaped with apex directed anteriorly; frontomaxillary suture medially concave or rarely straight; interparietal subcircular; basisphenoid wide; tympanic bullae large.
Comparisons.—From Liomys irroratus alleni, acutus differs as follows: Color slightly darker brown on upper parts; size slightly less; posterior border of nasals V-shaped rather than truncate; frontomaxillary suture medially concave or straight instead of convex; interparietal subcircular (anterior border) rather than triangular; basisphenoid broader; tympanic bullae larger and more inflated. From Liomys irroratus jaliscensis (topotypes), acutus differs as follows: Color slightly darker brown on upper parts; size larger, without overlap, in external measurements and in basilar length, length of nasals and mastoid breadth; posterior border of nasals V-shaped rather than almost truncate; frontomaxillary suture medially concave or straight rather than convex; interparietal subcircular rather than quadrilateral; basisphenoid wider; tympanic bullae larger. From Liomys irroratus pullus, acutus differs in longer body, shorter tail, slightly longer hind foot; all of upper parts, and especially upper side of tail, more brownish and less blackish; posterior border of nasals and frontomaxillary suture differing in same way as from alleni; interorbital region narrower in relation to length of skull; over-all length of skull greater; interparietal anteroposteriorly longer; tympanic bullae more inflated.
Figs. 4-6. Three views of the skull of the type specimen of Liomys irroratus
acutus. × 1.
Remarks.—This relatively large, dark-colored, spiny pocket mouse of east-central Michoacán differs from its geographic neighbors in V-shape of posterior border of nasals, semicircular shape of interparietal, medially concave maxillofrontal suture, wide basisphenoid and larger tympanic bullae. The latter character is not constant. Intergradation with L. i. alleni is shown by specimens from Querendaro in which the shape of the interparietal is exactly intermediate between those of topotypes of the two subspecies and also in that the basisphenoid is wider than in acutus but narrower than in alleni. Intergradation with L. i. jaliscensis is shown, by specimen No. 120275 (U. S. N. M.) from Zamora, in shape of posterior end of nasals, direction of maxillofrontal suture, and shape of interparietal. In each of these features the specimen from Zamora is almost exactly intermediate between acutus and jaliscensis. In large size of tympanic bullae and wider basisphenoid the specimen agrees with acutus, but otherwise is nearly as small as jaliscensis to which it is here referred. Actually the specimen could, with almost equal propriety, be referred to either subspecies.
Measurements.—The measurements of two males, Nos. 100184, 100182, and average and extreme measurements of five females, are, respectively, as follows: Total length, 257, 267, 244 (230-251); length of tail, 130, 128, 122 (105-129); length of hind foot, 32, 31, 31 (30-33); length of ear from notch, 16, 17, 15.3 (13.0-19); weight in grams, 71.5, 65.1, 50.8 (44.8-61.8); greatest length of skull, 35.2, 34.9, 33.6 (32.7-34.2); zygomatic breadth, 17.7, 17.5, 16.5 (16.1-17.1); interorbital breadth, 8.4, 8.1, 7.8 (7.5-8.0); length of nasals, 15.1, 14.9, 14.0 (13.3-14.5); width of braincase, 15.9, 15.1, 15.0 (14.7-15.1); alveolar length of upper molariform tooth-row, 6.0, 6.0, 5.6 (5.5-5.9). The measurements were taken according to the method of Goldman (N. Amer. Fauna, 34:10, 1911). Each of the specimens of which measurements are given above is adult; the transverse enamel fold has been obliterated in M1, is represented by only an isolated lake in M2 (except in one female where all trace of the fold has worn away) and is present in M3.
Specimens examined.—Total, 16, all from Michoacán, Mexico, and unless otherwise indicated in the University of California Museum of Vertebrate Zoölogy, as follows: 3 mi. NW Pátzcuaro, 6700 ft., 1; 2 mi. W Pátzcuaro, 7700 ft., 5; 2 mi. W Pátzcuaro, 6700 ft., 2; Pátzcuaro, 1 (U. S. Nat. Mus.); 5 mi. S Pátzcuaro, 7800 ft., 7.
For the loan of comparative materials we are grateful to Dr. Harold E. Anthony of the American Museum of Natural History, [Pg 255] Mr. Stanley P. Young and Dr. Hartley H. T. Jackson of the Biological Surveys Collection in the United States National Museum, Dr. Charles P. Lyman of the Museum of Comparative Zoölogy, and for assistance with the field work to the John Simon Guggenheim Memorial Foundation and to Miss Annie M. Alexander.
Transmitted April 1, 1948.