Geographic Distribution of the Pocket Mouse, Perognathus fasciatus

by J. Knox Jones

Specimens from the eastern part of the range of P. f. fasciatus are somewhat smaller and slightly darker than topotypes from Buford, North Dakota. Specimens from 9 mi. SE Bainville, Johnson Lake and 3 mi. S Medicine Lake, Montana, and from Crosby, North Dakota, are also paler than those from farther east. At the southern limit of the range of the subspecies, specimens from the Rosebud Agency and Minichaduza River, South Dakota, approach olivaceogriseus in pale dorsal coloration.

Specimens examined.—Total number, 83, as follows: Manitoba: Aweme, 3 (USBS 2, NMC 1). Junction of Antler and Souris rivers, 1 (NMC). Oak Lake, 2 (NMC). Montana: Roosevelt County: 9 mi. SE Bainville, 4 (MZ); Johnson Lake, 2 (USBS). Sheridan County: 3 mi. S Medicine Lake, 1880 ft., 1 (KU). Nebraska: Cherry County: Ft. Niobrara Game Reserve, 1 (NSM); Sparks, 1 (MZ); Valentine, 2 (UNDZ). North Dakota: Benson County: 2 mi. W Fort Totten, 1400 ft., 3 (KU). Bottineau County: Bottineau, 1 (CNHM). Burleigh County: 9 mi. E Bismark, 7 (MZ). Dickey County: Oakes, 2 (CNHM 1, USBS 1). Divide County: Crosby, 1 (USBS). Kidder County: Dawson, 1 (USBS); 6 mi. W Steele, 6 (MZ). McHenry County: 1/2 mi. E Upham, 1 (USBS). Morton County: 12 mi. W Mandan, 2 (MZ). Oliver County: Ft. Clark, 8 (USBS). Sargent County: 7-2/10 mi. E, 1-2/10 mi. S Oakes, 1200 ft., 1 (KU). Sioux County: Cannon Ball, 6 (USBS). Stark County: 1 mi. S Dickinson, 1 (MZ); 9 mi. W Dickinson, 3 (MZ); 2 mi. W Taylor, 4 (MZ). Stutsman County: 7 mi. N Jamestown, 1 (MZ); 14 mi. W Jamestown, 1 (MZ). Wells County: Bowdon, 1 (USBS). Williams County: Buford, 9 (USBS). South Dakota: Todd County: Minichaduza River, 2 (USBS); Rosebud Agency, 1 (USBS). Tripp County: Colome, 3 (MZ). Walworth County: Swan Creek, 13 mi. S Shelby, 1600 ft., 1 (KU).

Perognathus fasciatus olivaceogriseus Swenk

Perognathus flavescens olivaceogriseus Swenk, Missouri Valley Fauna, 3:6, June 5, 1940, type from [Little Bordeaux Creek, sec. 14, T. 33 N, R. 48 W, 3 mi. E] Chadron, Dawes County, Nebraska.

Geographic distribution.—Southeastern Alberta, southeast to eastern Wyoming and adjacent parts of South Dakota and Nebraska.

Diagnosis.—External measurements of the holotype and average and extreme external measurements of six adults (five males and one female) from several localities in eastern Wyoming are, respectively, as follows: Total length, 124, 132 (125-140); length of tail-vertebrae, 53, 63 (59-68); length of hind foot, 16.5, 17 (17-18); length of ear, 6.5, 6.6 (6.0-7.0). Color: Upper parts Cream Buff, lined with black and giving a pale olivaceous appearance; lateral line near (16'd) Light Ochraceous-Buff; postauricular patches Cream Buff; subauricular patches and underparts white; tail indistinctly bicolor, dusky above, whitish below. Skull: Size medium for species (see Table 1); braincase and auditory bullae moderately inflated; interorbital region narrow; mastoidal region broad.

Remarks.—From topotypes of Perognathus fasciatus fasciatus, geographically adjacent to the northeast, P. f. olivaceogriseus differs in: Upper parts paler, especially face which is heavily washed with buff; hind foot smaller; skull averaging slightly smaller in all measurements taken (especially least interorbital breadth and cranial depth), except mastoidal breadth which is slightly more and interparietal breadth, length of tympanic bulla and length of maxillary tooth-row which are approximately the same. From topotypes of Perognathus fasciatus infraluteus, geographically adjacent to the south, P. f. olivaceogriseus differs in: Upper parts paler and less drab; lateral line brighter and more ochraceous; underparts never buffy; skull averaging larger in all measurements taken except interparietal breadth and length of maxillary tooth-row which are smaller. From topotypes of Perognathus fasciatus litus, geographically adjacent to the southwest, P. f. olivaceogriseus differs in: Upper parts darker; skull, when specimens of equal age are compared, averaging larger in mastoidal breadth, interparietal breadth and basal length. From topotypes of Perognathus fasciatus callistus, P. f. olivaceogriseus differs in: Upper parts slightly darker, pelage not silky, coarser in appearance; hind foot shorter; skull averaging smaller in all measurements taken (especially mastoidal breadth), except interparietal breadth which is more.

Swenk (loc. cit.) originally described P. f. olivaceogriseus as a subspecies of Perognathus flavescens. I have examined the holotype, kindly made available to me by Dr. Seth B. Benson of the Museum of Vertebrate Zoology, University of California, and the paratype, in the collection of the University of Nebraska State Museum. Neither is P. flavescens, but both are clearly specimens of P. Fasciatus on the basis of olive-gray dorsal coloration, larger over-all dimensions of the skull, and in that the tympanic bullae do not meet anteriorly. In addition, a third specimen from Glen, Nebraska, purported by Swenk to be intermediate between flavescens and olivaceogriseus, has been examined and found to be an immature fasciatus.