BY HENRY W. SETZER University of Kansas Publications Museum of Natural History Volume 1, No. 23, pp. 473-573, 27 figures in text, 7 tables December 27, 1949 University of Kansas LAWRENCE 1949 University of Kansas Publications, Museum of Natural History Editors: E. Raymond Hall , Chairman, A. Byron Leonard, Edward H. Taylor, Robert W. Wilson Volume 1, No. 23, pp. 473-573, 27 figures in text, 7 tables December 27, 1949 University of Kansas Lawrence, Kansas PRINTED BY FERD VOILAND, JR., STATE PRINT

The geographic range of the kangaroo rats, genus Dipodomys , extends from southern Canada south to the southern limits of the Mexican Tableland and from the Pacific Coast east to the eastern limits of the Great Plains in Kansas, Oklahoma and Nebraska. These animals are usually restricted to sandy soils in semiarid regions. The species Dipodomys ordii , with which this account is primarily concerned, is, to the best of my knowledge, almost exclusively confined to sandy areas. Since 1841, when Gra

Available specimens were arranged according to geographic origin. These were segregated as to sex and then under each sex by age. Individual variation was next measured in each of several samples in which individuals were of like geographic origin, sex, age and season. Finally, comparable materials were arranged geographically for detection of variations of systematic worth. Following preliminary studies of material thus arranged, additional specimens were collected from critical areas. When ful

The family Heteromyidae was defined by Wood (1935:81) essentially as follows: Cheek teeth brachydont to hypsodont and even rootless; usually six cusps per molar, three on each loph; enamel rarely divided into two plates, never reduced to one; skull light, thin and papery; mastoids inflated, mastoidal breadth often greatest, never appreciably less than zygomatic breadth; interorbital space wider than rostrum; palate nearly horizontal and little if any below level of zygomata; nasals extended beyo

Skeletal Indices of Dipodomys The right kidney is variable in position in reference to the left. In all species the right kidney lies anterior to the left but in some, D. deserti and D. ingens , it is markedly anterior. In Dipodomys agilis , D. merriami and D. deserti there are small to large patches of lymphoid tissue on the caecum. These patches were not noted in any of the other species examined and I do not know their function. In the three above mentioned species, however, the large intesti

From the differences noted in the skeleton, in the entire visceral mass, and in the shape and position of the liver it appears that as a saltator becomes more specialized skeletally, there is a concurrent compacting and aligning of the viscera into a more or less bilaterally balanced mass. It seems that this alignment is for a stabilization in leaping. It seems reasonable that the individual that has a loose and unconsolidated visceral mass, or in which the viscera or at least the heaviest part

Relative Specializations of the Species for each Index The figure 1 represents the least specialized condition for the index, while the figure 11 represents the most specialized condition. The remainder of the numbers indicate the relative degree of specialization of each species for each index. The species that have been examined are listed in Table 3 in increasing order of specialization from top to bottom. Usually animals of extreme morphological specialization are much restricted environment

If we assume the region of origin and center of dispersal of a group of animals to be the one in which the greatest numbers of the most specialized species of a given genus are found, then the northern Tableland of Mexico and the adjoining region of the United States in southeastern California and southwestern Nevada is the region of origin and the center of dispersal for the genus Dipodomys . Dipodomys deserti , Dipodomys merriami , Dipodomys panamintinus , Dipodomys microps , Dipodomys phillip

The first three columns represent the actual measurements of the various elements; the fourth column is the index established. Six different complexes (groups) of subspecies of D. ordii have probably arisen as a result of geographical separation. The Great Plains complex consisting of D. o. richardsoni , D. o. oklahomae , D. o. evexus , D. o. terrosus , D. o. luteolus , D. o. priscus and D. o. medius are, with the exception of D. o. priscus , inhabitants of the high plains grassland habitat. D.

Indices for the Subspecies of DIPODOMYS ORDII...

Numerals (derived from Table 5 ) are Indicative of the Relative Degree of Specialization of the Subspecies of DIPODOMYS ORDII...

Ord Kangaroo Rat Dipodomys ordii is a medium sized, relatively short-tailed, five-toed species of a color about average for the genus. As in other members of the genus, the hind legs and feet are disproportionately long as an adaptation to the saltatorial mode of progression. The upperparts are buffy, reddish or blackish, depending on the subspecies, but the entire ventral surface, dorsal surfaces of the hind feet, supraorbital and postauricular spots, forelimbs, hip stripes, lateral stripes of

  1. There are thirty-five recognizable subspecies of the species Dipodomys ordii of which four are herein, for the first time, recognized by name. Three subspecies, D. o. oklahomae , D. o. sennetti and D. o. compactus , previously were regarded by most authors as full species.   2. The species Dipodomys ordii is divisible into six complexes, or groups, of subspecies on both geographic and morphological bases.   3. Dipodomys ordii is the most generalized Recent species of the genus.   4. The ext

Measurements (in Millimeters) of Dipodomys ordii D. o. richardsoni 1-1/2 mi. N Beaver, Oklahoma (KU) ♂ Mean (4) 251.2 131.5 40.5 41.0 24.7 22.0 4.3 14.9 13.0 26.3 Maximum 256 136 41 41.8 25.1 22.3 4.5 15.4 13.2 27.3 Minimum 243 133 40 40.4 24.4 21.5 4.2 14.6 12.7 26.0 ♀  KU 17962 253 135 42 40.6 25.4 22.6 4.6 15.1 14.2 25.7 KU 17963 246 133 40 39.4 24.0 ... 4.3 14.1 12.5 25.6 KU 17963 255 136 41 41.2 25.5 22.1 4.5 15.1 13.8 26.2 D. o. oklahomae 2-1/4 mi. S Norman, Oklahoma (USBS) ♂ Mean (4) 239.