Subspeciation in the Kangaroo Rat, Dipodomys ordii / KU. Vol 1 No 23

by Henry W. Setzer

From Dipodomys ordii oklahomae, D. o. richardsoni differs as follows: Size larger in all measurements taken; color darker in all pigmented areas; skull larger in all respects; auditory bullae larger and more inflated ventrally; jugal straight or nearly so instead of bowed laterad; pterygoid fossae smaller; nasals straight instead of inflated as a "bulb" distally.

For comparisons with D. o. montanus and D. o. evexus, see accounts of those subspecies.

Remarks.—This race of Dipodomys ordii is readily distinguished from Dipodomys ordii evexus, from the valley of the upper Arkansas River, by larger size, larger skull and lighter color. Intergradation with Dipodomys ordii luteolus occurs rather freely in northeastern Colorado, as indicated by specimens from 3 miles northeast of Fitzsimmons, 6 miles east and 1 mile north of Denver and Barr Lake. These specimens resemble D. o. richardsoni in light color, greater inflation of the auditory bullae and the shape of the pterygoid fossae but resemble D. o. luteolus, to which they are here referred, in the length of the nasals, the least interorbital width and in the external measurements. In the southern part of the range of D. o. richardsoni intergradation occurs with Dipodomys ordii medius, as at 6 miles southwest of Muleshoe, Texas. Specimens from there have the long, wide rostrum and narrow skull of D. o. richardsoni but in the sum total of their characters more closely resemble D. o. medius. At Texline, Texas, the animals show intergradation in the length and shape of the nasals and degree of convexity of the cranium but are referable to D. o. richardsoni.

In fine, intergradation occurs at all points where the range of D. o. richardsoni touches that of any other geographic race. No one series of it is as uniform as are most series of specimens of other known races. Dipodomys ordii richardsoni shows a mixture of characters. Nevertheless, each of the populations studied has characters in most of the animals that make this form recognizable as a taxonomic unit—a unit that seems, as yet, not to have become stabilized even in the central parts of its range.

[Coues and Allen] (1877:542) list specimens from Fort Cobb, Arkansas. It is known that the Post Office Department, for administrative purposes, attached certain towns and military installations in Indian Territory (now Oklahoma) to the State of Arkansas. Thus it is apparent that Fort Cobb, Arkansas, as recorded by [Coues and Allen] (loc. cit.) is Fort Cobb, Oklahoma. Specimens from Fort Cobb would be expected to be D. o. richardsoni.

Specimens examined.—Total, 351, distributed as follows:

Nebraska: Adams County: Bladen, 10 (AMNH). Dundy County: Haigler, 1 (USBS).

Colorado: Crowley County: Olney, 1 (USBS). Kiowa County: Chivington, 3 (USBS). Otero County: 18 mi. S La Junta, 4 (AMNH); Higbee, 1 (USBS). Bent County: 4 mi. SE Las Animas, 4100 ft., 3 (MVZ). Prowers County: Lamar, 9 (LACM); 1 mi. S Lamar, 4000 ft., 11 (KU). Baca County: Gaumes Ranch, 4600 ft., NW Corner, 1 (USBS).

Kansas: Cheyenne County: 23 mi. NW St. Francis, 5 (KU). Rawlins County: 2 mi. NE Ludell, 2 (KU); 1-1/2 mi. W Ludell, 1 (KU). Wallace County: Lacey Ranch, 4-1/2 mi. E and 9 mi. S Wallace, 1 (KU); unspecified, 2 (KU). Logan County: 5 mi. W Elkader, 2 (KU); unspecified, 1 (UM). Gove County: unspecified, 1 (KU). Trego County: Banner, 8 (USNM); Parrington Ranch, 12 mi. S Collyer, 2 (KU); unspecified, 8 (USNM). Ellis County: Ellis, 1 (USBS). Lane County: Pendennis, 10 (USBS). Hamilton County: Coolidge, 2 (CNHM); 1 mi. E Coolidge, 5 (KU). Pawnee County: 1 mi. S Larned, 4 (KU); 2 mi. S and 1/4 mi. W Larned, 2 (KU); 3 mi. S and 1-1/2 mi. W Larned, 10 (KU). Edwards County: Kinsley, 3 (USBS); 3-1/2 mi. E Kinsley, 5 (KU); S side Arkansas River, 2 mi. S Kinsley, 1 (KU); 1 mi. W and 3-1/2 mi. S Kinsley, 9 (KU). Stafford County: Little Salt Marsh, 15 mi. N and 3 mi. E Stafford, 2 (KU). Reno County: Medora, 1 (UM); 2 mi. W and 1/2 mi. S Medora, 4 (KU). Kiowa County: 5 mi. N Belvidere, 1(KU). Pratt County: Cairo, 2 (USBS). Sedgwick County: Wichita, 6 (AMNH). Morton County: 10 mi. N and 3 mi. E Elkhart, 34-1/2 (KU). Seward County: 1 mi. E Arkalon, 7 (KU); Liberal, 1 (KU); unspecified, 1 (KU). Meade County: Meade, 1 (USNM); 13 mi. SW Meade, 13 (6 AMNH; 7 KU); 17 mi. SW Meade, 2 (KU). Clark County: 12 mi. S Ashland, 1 (UM); unspecified, 3 (KU). Barber County: Medicine Lodge, 4 (USBS); 1 mi. W Aetna, 3 (KU); 1/2 mi. W Aetna, 2 (KU); Aetna, 3 (KU); 1 mi. SW Aetna, 1 (KU); 1-1/2 mi. SW Aetna, 1 (KU); 1 mi. S Aetna, 5 (KU); unspecified, 2 (KU). Harper County: 4-1/2 mi. NE Danville, 12 (KU); 2 mi. NE Runnymede, 3 (KU).

New Mexico: Union County: Clayton, Apache Canyon, 1 (USBS). Quay County: Glenrio, 10 (LACM).