Subspeciation in Pocket Gophers of Kansas

By
BERNARDO VILLA-R. and E. RAYMOND HALL

University of Kansas Publications
Museum of Natural History

Volume 1, No. 11. pp. 217-236
November 29, 1947

UNIVERSITY OF KANSAS
LAWRENCE
1947

University of Kansas Publications Museum of Natural History
Editors: E. Raymond Hall, Chairman, H. H. Lane, and Edward H. Taylor
Volume 1, No 11. pp. 217-236
Published November 29, 1947

University of Kansas
Lawrence, Kansas

PRINTED BY
FRED VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS
  1947

21-8188

Subspeciation in Pocket Gophers of Kansas

By

BERNARDO VILLA-R. AND E. RAYMOND HALL

Several full species of the genus Geomys have been recorded from Kansas. The purpose of the study now reported upon was to determine the present taxonomic status of these animals and the distribution of each within the boundaries of Kansas. No pocket gopher of any kind has been reported from the southeastern part of the state; in all other parts Geomys is locally common.

HISTORY

The first published reference that we have found to pocket gophers of Kansas is Prof. Spencer F. Baird's (1857:377, 380) mention of two specimens from Fort Riley. One he identified as Geomys bursarius (p. 377) and the other (p. 380) he doubtfully referred to Geomys breviceps. Both specimens were obtained by Dr. W. A. Hammond. J. A. Allen (1874:49) reported pocket gophers from Kansas under the generic name "Geomys?". Professor M. V. B. Knox (1875:21) published a list of Kansas mammals in which he used the names Geomys bursarius Shaw and Geomys breviceps Baird, the last one for the specimen taken by Dr. Hammond, at Fort Riley. Baker (1889:57) employed the name Geomys bursarius Rich. for the gopher "found along the hundredth meridian, between N latitude 38° 30' and 39° 30'." He reported this animal as common in western Kansas. Merriam (1895:129) recorded G. bursarius and G. lutescens from Kansas. Allen (1895:265) recorded five specimens of Geomys lutescens collected between September 16 and October 13 at Long Island, Phillips County, Kansas, by W. W. Granger. Since that time several papers, some of them dealing mostly with habits of pocket gophers, have been published in which reference is made to Geomys in Kansas. Hibbard (1933:240) recognized three species: G. bursarius, G. lutescens, and G. breviceps llanensis. In 1944 (74-75) he recorded Cratogeomys from Meade County, on the basis of two skulls dug out of the ground, and he recognized the same three full species of the genus Geomys that he did in 1933, along with two additional subspecies.

Specimens to the total number of 335 from Kansas have been available for the present study of the five subspecies recognized. The reason for arranging all of the named kinds as subspecies of a single species is that intergradation has been found to occur between every pair of kinds having contiguous geographic ranges. The characters previously thought by some writers constantly to differentiate, say, Geomys lutescens of western Kansas from Geomys bursarius of eastern Kansas, prove not to do so; instead, in areas geographically intermediate between the geographic ranges of the two kinds, the pocket gophers are intermediate in morphological characters and therefore are regarded as intergrades. Intergradation of this kind here is accepted as the criterion of subspecies, and lack of such intergradation as the criterion of species. Search for structural characters, distinctive of the different kinds, additional to those characters noted by other writers, has resulted in the finding of a few such characters but they too are subject to intergradation. Therefore the several kinds are arranged as subspecies of a single species which takes the name Geomys bursarius because it is the oldest available name. Detailed comment on specimens showing intergradation are to be found in the accounts of G. b. bursarius and G. b. major.

METHODS AND ACKNOWLEDGEMENTS

The series with the largest number of individuals from one restricted locality was selected for initial study. These individuals were segregated by sex, and specimens of each sex were arranged from oldest to youngest. Each series was divided into age-groups, and within a given age-group of one sex from one locality of what was considered as one species, estimation was made of the amount of individual variation. Thus, it was possible when comparing different kinds of pocket gophers to use only one age class of one season of one sex.

Age was estimated to some extent by size of animal and nature of its pelage. The immature pelage is grayer and the hair is more crinkled than in adults. A more certain guide to age, however, is furnished by the skull. With increasing age some sutures disappear, the rostrum increases in length and the ridges marking the limits of the temporal muscles come to fuse and eventually, in males, form a high sagittal crest.

Cranial measurements were taken as follows:

Basilar length.—From the anteriormost inferior border of the foramen magnum to a line connecting the posteriormost margins of the alveoli of the first upper incisors.

Length of the nasals.—The greatest length of the nasals.

Zygomatic breadth.—The greatest distance across the zygomatic arches.

Mastoid breadth.—The greatest distance across the mastoids.

Breadth of rostrum.—Width, perpendicular to long axis of the skull.

Interorbital constriction.—The least distance between the orbits.

Maxillary tooth row.—The greatest length of the upper molariform tooth row at the alveolar border.

Extension of premaxillae posterior to nasals.—From the posteriormost border of the nasals to the posterior end of the extension of a premaxilla.

Depth of skull.—From the median suture of the frontals, on the dorsal surface of the skull to the median suture of the palatines at the level of the first molar (not premolar).

Length of rostrum.—From the anterior border of the nasal to the maxilla at the lateral end of the hamulus of the lacrimal.

In the list of specimens examined, localities are arranged by counties from west to east, beginning at the northwestern corner of the state; specimens in each county are arranged from north to south. If several localities are in the same latitude, the westernmost is listed first. Capitalized color terms are after Ridgway, Color Standards and Color Nomenclature, Washington, D. C., 1912.

Fig. 1. Map showing the geographic distribution of the five subspecies of the Missipi Valley pocket gopher, Geomys bursarius, in Kansas, with insert showing range of the species.

In connection with this study each of the authors acknowledges assistance from the John Simon Guggenheim Memorial Foundation and one of us (Villa) is grateful