Subspeciation in the Kangaroo Rat, Dipodomys ordii / KU. Vol 1 No 23 - Henry W. Setzer

	Humeroradial	Intermembral	Crural	Tibioradial	Femorotarsal-metatarsal	Cranial	Average
ordii	5	1	1	1	1	5	2.33
microps	1	2	4	5	4	2	3.0
panamintinus	6	3	3	3	3	1	3.1
agilis	7	4	5	6	6	4	5.3
heermanni	3	6	7	9	5	3	5.5
ingens	4	7	2	8	2	10	5.5
spectabilis	2	11	6	11	7	8	7.5
phillipsii	11	5	10	2	11	7	7.6
merriami	10	9	9	4	10	6	8.0
nitratoides	9	8	8	7	9	9	8.5
deserti	8	10	11	10	8	11	9.6

Figs. 11-15. Ventral views of skulls showing the degree of development of the auditory bullae and the configuration of the pterygoid fossae. All figures approximately × 1.

Fig. 11. Dipodomys ordii compactus, [M], adult, no. 646, TCWC; 19 mi. S Port Aransas, Mustang Island, Nueces County, Texas; 24 April, 1939.

Fig. 12. Dipodomys ordii oklahomae, [F], adult, no. 265456, USBS; 2-1/4 mi. S Norman, Cleveland County, Oklahoma; 21 March, 1934.

Fig. 13. Dipodomys ordii richardsoni, [F], adult, no. 15995, KU; 1 mi. S Lamar, Prowers County, Colorado; 8 September, 1945.

Fig. 14. Dipodomys ordii nexilis, [F], adult, no. 149941, USBS; 5 mi. W. Naturita, Montrose County, Colorado; 20 July, 1907.

Fig. 15. Dipodomys deserti deserti, [F], adult, no. 18670, KU; 14 mi. WSW Fallon, Churchill County, Nevada; 3 November, 1945.

Figs. 11-15. Ventral views of skulls showing the degree of development of the auditory bullae and the configuration of the pterygoid fossae. All figures approximately × 1.
	Fig. 11. Dipodomys ordii compactus, [M], adult, no. 646, TCWC; 19 mi. S Port Aransas, Mustang Island, Nueces County, Texas; 24 April, 1939.
	Fig. 12. Dipodomys ordii oklahomae, [F], adult, no. 265456, USBS; 2-1/4 mi. S Norman, Cleveland County, Oklahoma; 21 March, 1934.
	Fig. 13. Dipodomys ordii richardsoni, [F], adult, no. 15995, KU; 1 mi. S Lamar, Prowers County, Colorado; 8 September, 1945.
	Fig. 14. Dipodomys ordii nexilis, [F], adult, no. 149941, USBS; 5 mi. W. Naturita, Montrose County, Colorado; 20 July, 1907.
	Fig. 15. Dipodomys deserti deserti, [F], adult, no. 18670, KU; 14 mi. WSW Fallon, Churchill County, Nevada; 3 November, 1945.

Figs. 16-20. Dorsal views of skulls showing the degrees of inflation of the auditory bullae and the correlation of large bullae with small interparietal. All figures approximately × 1.

Fig. 16. Dipodomys ordii compactus, for data see [Fig. 11].

Fig. 17. Dipodomys ordii oklahomae, for data see [Fig. 12].

Fig. 18. Dipodomys ordii richardsoni, for data see [Fig. 13].

Fig. 19. Dipodomys ordii nexilis, for data see [Fig. 14].

Fig. 20. Dipodomys deserti deserti, for data see [Fig. 15].

Figs. 16-20. Dorsal views of skulls showing the degrees of inflation of the auditory bullae and the correlation of large bullae with small interparietal. All figures approximately × 1.
	Fig. 16. Dipodomys ordii compactus, for data see [Fig. 11].
	Fig. 17. Dipodomys ordii oklahomae, for data see [Fig. 12].
	Fig. 18. Dipodomys ordii richardsoni, for data see [Fig. 13].
	Fig. 19. Dipodomys ordii nexilis, for data see [Fig. 14].
	Fig. 20. Dipodomys deserti deserti, for data see [Fig. 15].

[Grinnell's] arrangement				Present arrangement
Heermanni Group				Heermanni Group
Dipodomys heermanni				Dipodomys heermanni
Dipodomys morroensis				Dipodomys agilis
Dipodomys mohavensis				Dipodomys ingens
Dipodomys leucogenys				Dipodomys venustus
Dipodomys panamintinus				Dipodomys elephantinus
Dipodomys stephensi
Dipodomys ingens
Spectabilis Group				Spectabilis Group
Dipodomys spectabilis				Dipodomys nelsoni
Dipodomys spectabilis				Dipodomys nelsoni
Phillipsii Group				Now in Merriami Group Below
Dipodomys phillipsii
Dipodomys perotensis
Dipodomys ornatus
Dipodomys elator
Merriami Group				Merriami Group
Dipodomys merriami				Dipodomys merriami
Dipodomys nitratoides				Dipodomys nitratoides
Dipodomys platycephalus				Dipodomys platycephalus
Dipodomys margaritae				Dipodomys margaritae
Dipodomys insularis				Dipodomys insularis
Dipodomys mitchelli				Dipodomys mitchelli
				Dipodomys phillipsii
				Dipodomys ornatus
				Dipodomys elator
Ordii Group				Ordii Group
Dipodomys ordii				Dipodomys ordii
				Dipodomys microps
Compactus Group				Now in Ordii Group Above
Dipodomys compactus
Dipodomys sennetti
Agilis Group				Now in Heermanni Group Above
Dipodomys agilis
Dipodomys venustus
Dipodomys elephantinus
Microps Group				Now in Ordii Group Above
Dipodomys microps
Dipodomys levipes
Deserti Group				Deserti Group
Dipodomys deserti				Dipodomys deserti
Were in Heermanii Group Above				Panamintinus Group
				Dipodomys panamintinus
				Dipodomys stephensi

In view of the foregoing evidence it seems best to estimate the relationships and history of the various species and groups of species only as far back as the early Pleistocene (see [Figure 21]). Inasmuch as faunas of fossil mammals from the mid-Pleistocene contain few, if any, Recent species (see [Hibbard], 1937:193), the living species of Dipodomys have probably had a geologic history no longer than the period of time which has elapsed since the middle Pleistocene, or at the earliest the early Pleistocene. Of the Recent species, only Dipodomys agilis is known as a fossil; it was found in the late Pleistocene tar pits of California. Under the heading "Dipodomys near ingens," however, [Schultz] (1938:206) recorded remains of kangaroo rats from the tar seeps of McKittrick in the San Joaquin Valley of California.

[DISPERSAL OF THE SEVERAL SPECIES]

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 phillipsii and Dipodomys ordii are found in the region mentioned. That the aforementioned region may be the center of differentiation for this genus is further indicated by: First, the finding, in this region, of saline deposits of Cenozoic (Miocene) age, indicating aridity, which is thought to have been one of the essential stimuli for the development of the saltatorial habit in the genus Dipodomys; second, the recovery of the advanced heteromyids from the Avawatz and Ricardo of the Clarendonian (Pliocene) of this same region; and third, the present abundance and diversification of kangaroo rats in this same geographic region which has been more or less arid since Miocene time.

A secondary center of evolution has been the low, hot interior valleys and adjacent foothills of central California where Dipodomys ingens, Dipodomys heermanni, Dipodomys venustus, Dipodomys agilis, Dipodomys elephantinus and Dipodomys nitratoides are now found. Although there are as many species as in the principal center of origin, the amount of specialization and adaptive radiation in California is not so great. Probably during the Quaternary, when the process of mountain building was actively under way the animals that had reached central California from the parental center became isolated by the emergence of the Tehachapi Mountains. This mountain range separated the California animals from populations farther south and east. As a result, D. nitratoides was differentiated from D. merriami, and D. heermanni underwent an evolution of its own which resulted in animals having either four or five toes on the hind foot. At the same time Dipodomys ingens developed there and has since been undergoing an evolution parallel to that of the large-sized species, Dipodomys spectabilis. The two species have paralleled each other not only in large size but to some extent in habits such as building large mounds that are kept free of vegetation and in occupying areas of rather hard clayey soil. Structurally, however, D. ingens has not yet become quite so specialized as D. spectabilis, probably because D. ingens has had less time in which to become so. A second species, if it is a full species, Dipodomys elephantinus, has also been isolated in central California but has not attained so high a degree of specialization as D. ingens. It is interesting to note that in each of the two stocks, two large-sized species have been evolved. In the parental stock the two species are Dipodomys deserti and Dipodomys spectabilis; the former is the most specialized species in the genus. In the stock isolated in California, however, even though two large species have been formed they are still below the average in degree of specialization for the genus. As noted elsewhere in this paper, the species from these low, hot valleys, excepting D. nitratoides, are all closely related one to another. Dipodomys venustus and Dipodomys elephantinus are either closely related species or possibly only subspecies of one species, Dipodomys agilis.

It is worthy of note that as the distance away from the center of differentiation increases, the number of species decreases. For example, in the northern Great Basin there are only two species (Dipodomys ordii and Dipodomys microps) and farther eastward, on the eastern side of the Rocky Mountains, there is only the one species, Dipodomys ordii. In north-central Texas, Dipodomys elator, perhaps a relict species, is found occupying an area farther east than that occupied by Dipodomys ordii at that latitude.

Dipodomys ordii, Dipodomys phillipsii and Dipodomys merriami occupy the southern portion of the range of the genus. Instead of being generalized at this southern part of the periphery of the range as are the kinds found on the other parts of the periphery of the range of the genus, these three southern kinds are notably specialized there in the south. The subspecies D. o. palmeri which occurs in the area, is the most specialized of the species Dipodomys ordii; and Dipodomys phillipsii and Dipodomys merriami stand high in the scale of specialization with respect to the other species of the genus. The reason for this is not clear.

[SUBSPECIATION]

Dipodomys ordii is, without question, a valid species if one accepts [Mayr's] (1942:120) definition that "Species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups." D. ordii is not known to hybridize with other species where their geographic ranges are adjacent or overlap. The first part of the definition "actually or potentially interbreeding populations" is substantiated by the 35 recognizable subspecies which can be defined as "a complex of interbreeding and completely fertile individuals which are morphologically identical or vary only within the limits of individual, ecological and seasonal variability. The typical characters of this group of individuals are genetically fixed and no other geographic race of the same species occurs within the same range" (after Rensch, 1934; from [Mayr], 1942:106). Thus we find that certain populations of individuals differ from others and that in geographic areas between two of these populations, individuals (intergrades) are found which resemble those of both populations. In another instance, a population may be geographically isolated yet in its characters it may be recognizable as a subspecies without actual intergradation because of slight degrees of difference, or a group may be different from another without being geographically separated and may or may not show intergradation.

Subspeciation in Dipodomys ordii almost certainly has been effected, by means of mutations, under the influence of natural selection. Natural selection enhanced by geographic and ecologic isolation, probably has retained mutations of evolutionary significance, thus permitting the development of the many recognizable subspecies.

In the subspecies of Dipodomys ordii the color ranges from pale to dark. The difference in color is as pronounced as that between the full species D. deserti and D. heermanni. The lightest-colored subspecies are Dipodomys ordii celeripes, D. o. extractus and D. o. compactus; the darkest are D. o. obscurus and D. o. palmeri.

There is a marked tendency for intergrades between a light-colored subspecies, such as D. o. celeripes, and a dark-colored kind, such as D. o. utahensis, to show varying degrees of blending in color. The insular population, D. o. compactus, has, however, two distinct color phases, a light phase and a slightly darker phase, and shows no tendency toward blending. In other kinds of mammals, blending of color is known to be the result of the action of multiple alleles, but in the insular kangaroo rat (D. o. compactus) the color appears to be the result of either a reduced multiple allelomorphic complex or even a unit factor. The two color phases of this insular subspecies, which might be an expression of a unit factor, more probably are specializations in which the multiple alleles for color have been reduced. The probability that there is either a unit factor or a reduced number of alleles at work is suggested by the taking of more dark-colored than light-colored animals and by the absence of blending of color. This insular population has undoubtedly been derived from the mainland kangaroo rat, D. o. sennetti, which has the usual range of variation but, to my knowledge, there are no individuals of D. o. sennetti so light as the darkest animals of D. o. compactus from the islands.

Populations from a given locality are remarkably stable in color except the animals from Samalayuca, Chihuahua, which vary in color from individuals almost as light as D. o. compactus to animals that approach D. o. ordii in darkness of pelage.

The subspecies of D. ordii show no noticeable variation in the extent of the hip stripe, supraorbital and postauricular spots, basal white ring of the tail, lateral stripes of the tail or the extent of white on the venter and feet. There is, however, variation in the degree and extent of the arietiform facial markings. In Dipodomys ordii utahensis, D. o. cupidineus, D. o. obscurus and D. o. fuscus these markings are pronounced. In D. o. celeripes, D. o. pallidus, D. o. compactus and D. o. attenuatus these markings are either obliterated or nearly so.

In Dipodomys ordii, color does not seem to be correlated with amount of moisture or geography, but rather with color of soil. For example, all animals from the Bonneville Basin of western Utah, are light colored as are the soils; animals from the San Rafael Desert of eastern Utah are reddish, as is the soil. More striking extremes of this are shown by D. o. compactus of Padre and Mustang islands, Texas, which is pale-colored as is the sand on which it lives, and D. o. medius from east-central New Mexico and western Texas, which is reddish as is the soil there, which is derived from Permian rocks. In localities where alkaline soils are present, kangaroo rats may be found with a roseaceous cast to the pelage as a result of the action of the alkaline salts on the pigment of the hair. The roseaceous color is lost when the animal sheds the old pelage.

In the dorsal and ventral stripes of the tail, I find as much variation in the species D. ordii as [Grinnell] (1922:Fig. E, p. 14) recorded in the whole genus. In D. o. obscurus, D. o. fuscus and D. o. utahensis the stripes are complete to the distal end of the tail and dark, whereas in D. o. pallidus and D. o. celeripes the ventral stripe is either absent or nearly so and the dorsal stripe is pale.

Color as a taxonomic character is valuable in a broad sense, and is useful in placing an individual or a group of individuals in the subspecies to which they pertain. In most subspecies studied, color was quite uniform throughout the range of the animals, but in D. o. ordii and D. o. columbianus color is so variable that cranial features were relied on almost exclusively for the final diagnosis.

Among the subspecies of Dipodomys ordii there is relatively little variation in the length of the head and body. The smallest measurement is 95.5 mm. in D. o. idoneus and the largest is 118.3 mm. in D. o. richardsoni. The shortest tail is found to be 112.0 mm. in D. o. celeripes and the longest is 154.7 mm. in D. o. terrosus. The length of the hind foot varies from 35.0 mm. in D. o. idoneus to 44.5 mm. in D. o. nexilis.

Allen's Rule is not operative in the species D. ordii. According to this rule, shorter tails and smaller feet in conjunction with a large body would be expected as the more northerly limits of the species are approached, and conversely, smaller body and larger appendages would be expected as the southerly limits of the species are approached. This is not the case, however, since the subspecies D. o. terrosus ranges farthest north and has the longest tail, whereas D. o. celeripes, found in the central part of the range of the species, has the shortest tail. Again, in regard to the hind foot, the shortest is found in D. o. idoneus which is at the extreme south of the range of the species, whereas the longest hind foot is found in D. o. nexilis which occupies a nearly central position in the range.

Long tail and long hind foot would seem to be specializations for saltation and the two would be expected to be correlated. Actually there is no significant correlation in D. ordii. D. o. celeripes, in which the hind foot is near the mean for the species (39.8 as opposed to the mean of 40.7), has the shortest tail. D. o. compactus has a short tail (117.0 mm.) but a medium-sized hind foot. D. o. nexilis and D. o. terrosus have both a long hind foot and long tail.

Cranial measurements vary less, probably because one person can measure a series with a uniformly subjective error. External measurements, however, are liable to a greater degree of subjective error. The total length of the skull varies from 35.4 mm. in D. o. attenuatus to 41.3 mm. in D. o. terrosus. In no one series of adults from one locality, however, is the variation so marked as it is for the species as a whole. The usual range of variation in length of skull in any given series is not, as a rule, more than 2.5 mm.

Cranial indices (breadth across bullae/length of skull × 100) as established for random samples of the different species of the genus (exclusive of D. ordii) ranged from 60.8 to 67.6. In the subspecies of D. ordii the same index varies from 59.7 to 65.2 with an average of 63.4. In other words, the degree of specialization indicated by this one index, in a few subspecies of D. ordii, is almost as great as that in Dipodomys deserti, which on the basis of total morphology appears to be the most specialized species in the genus. Also, on the basis of this same index, some subspecies of D. ordii are more generalized than is any other species in the genus.

There is a general tendency for the nasals to decrease in length and the rostrum to decrease in width as the southern limits of the range of D. ordii are approached. In ascertaining the decrease in length of the nasals an index was obtained as follows: nasals/interorbital width × 100 (see [Table 4]). The width of the rostrum, however, does not decrease in the same degree, nor at the same rate, as does the length of the nasals. This decrease in length of the nasals and in width of the rostrum may be correlated with the mean annual relative humidity of the environment. It is known ([Howell] and Gersh, 1936:8) that desert rodents, more exactly kangaroo rats, have a water retention mechanism in the kidneys and walls of the urinary bladder which enables them more efficiently to conserve metabolic water. The significance of the decrease of the area of the nasal mucosa, which seems to be related to relative aridity, is not yet properly understood.

In no cranial feature other than shortened nasals and narrowed rostrum, does Dipodomys ordii show a gradation such that it might be termed a cline. Other parts of the skull that were measured do not vary greatly.

Perhaps the greatest amount of variation in the skull is in features which are not readily measurable by the usual physical means. The shape and size of the pterygoid fossae vary from almost round to rather ovoid in a given series of animals from one locality; the size and configuration of the zygomatic arches vary from slender to robust and from straight to curved laterally; the size of the lacrimal processes varies much in any given series, as do also the degree of expansion of the distal end of the nasals, the convexity of the braincase and the curvature of the upper incisors. In all instances where these features varied much, one size or shape was more pronounced in the series than any other size or shape. Thus, when comparisons were made, the size and certain shapes were the criteria used in assigning the animals under consideration to a given subspecies.

Subspeciation in Dipodomys ordii seems to have been influenced by water barriers. It is known ([Grinnell], 1922:28) that kangaroo rats lack the ability to swim. Large stable rivers such as the Colorado, Snake and Columbia serve as effective barriers to further dispersal of kangaroo rats. Streams that freeze over in the winter months, however, are not efficient barriers. This is indicated by the "blending" of morphological characters of D. o. nexilis and D. o. sanrafaeli along the Green River which freezes over.

Any mountain which has vegetational belts above the Transition Life-zone would serve as a barrier to the dispersal of these animals. The Uinta Mountains, lying in an east-west direction, are interposed between the ranges of D. o. priscus and D. o. uintensis. The high Wasatch Mountains and their associated outliers, lying in a north-south direction in Utah, serve as an efficient barrier to the east-west movement of kangaroo rats and as a result, the subspecies east of the mountain mass are remarkably different from those to the west.

TABLE 4

Proportionate Decrease of Nasals

Width of rostrum Length of nasals Least interorbital width Nasals
Interorbital × 100

terrosus 4.1 14.75 13.5 91.6

luteolus 4.35 13.9 12.95 93.1

evexus 4.3 14.35 13.75 94.8

montanus 4.1 13.5 12.65 93.8

ordii 3.5 13.3 13.0 97.7

idoneus 3.7 13.2 13.75 103.5

palmeri 3.3 12.8 13.0 101.1

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. o. priscus inhabits the red Desert of Wyoming.

The Gulf Coast complex, comprising D. o. sennetti and D. o. compactus are separable from all others by small auditory bullae and short tail. D. o. compactus probably has differentiated from D. o. sennetti since the cutting off, by wave action, from the mainland, of the islands on which D. o. compactus lives.

The Mexican complex consisting of D. o. obscurus, D. o. fuscus, D. o. idoneus and D. o. palmeri have probably differentiated by natural selection acting on fortuitous variations, but I lack first hand knowledge of the region concerned.

The southwestern complex consists of D. o. chapmani, D. o. extractus, D. o. attenuatus and D. o. ordii. D. o. attenuatus and D. o. chapmani are subspecifically distinct owing to geographic isolation, although both kinds show intergradation where their ranges approach that of D. o. ordii.

The western desert complex, composed of D. o. monoensis, utahensis, cineraceus, columbianus, cinderensis, fetosus, celeripes, marshalli, inaquosus, pallidus, panguitchensis and fremonti was isolated from the other complexes of D. ordii by the Quaternary uplift of the Wasatch Mountain mass, consisting of the Wasatch, Fish Lake and San Pitch mountains and the Wasatch, Aquarius, Paunsaugunt and Kaiparowits plateaus, and the concurrent reëstablishment of drainage systems. The drainages are those of the Colorado and Columbia rivers and that of the Snake River from Blackfoot, Idaho, to the junction with the Columbia. D. o. fremonti has been isolated on the upper reaches of the Fremont River which arises from the eastern side of the Wasatch Divide. D. o. panguitchensis has been isolated in Panguitch Valley as a result of the canyons formed by the Sevier River in Utah. D. o. cineraceus, although its subspecific and insular status are in doubt, appears to have been isolated on Dolphin Island, Great Salt Lake, Utah.

The intermontane complex consisting of D. o. montanus, longipes, cupidineus, nexilis, sanrafaeli and uintensis, like the western desert complex, has become separated from the remainder of the subspecies of the species D. ordii by Quaternary geologic events. D. o. cupidineus has been cut off by the gorges of the Colorado River to the south and the Virgin River to the north. D. o. sanrafaeli is separated from D. o. uintensis by the Tavaputs Plateau and by the Roan and Book cliffs, and is separated from the range of D. o. nexilis by the Colorado River although there is intergradation between D. o. nexilis and D. o. sanrafaeli. D. o. longipes has been separated from the rest of this intermontane complex by the San Juan and Colorado rivers, but to the east it intergrades freely with adjacent subspecies. D. o. montanus has been relatively isolated in the San Luis Valley of Colorado and New Mexico, but in the southern part of its range it does show intergradation with other subspecies.

Fig. 22. An arrangement, according to morphological indices, of the subspecies of Dipodomys ordii.

The complexes mentioned above are represented graphically in Figure 22, in a way that expresses some of my ideas as to their genetic relationships.

The indices used to determine the amount of specialization that each complex of subspecies has undergone are as follows:

The Body index (head and body/length of tail × 100) is the expression of the elongation of the tail as an organ of balance while the length of the head and body remain relatively constant. As the tail elongates the index decreases and as the tail becomes shorter the index increases.

The Pedal index (hind foot/head and body × 100) is the expression of the development of the hind foot as an element essential for the saltatorial habit. As the hind foot elongates the index will increase; elongation of the hind foot is interpreted as a specialization.

The Cranial index (breadth across bullae/length of the skull × 100) reflects the degree of development of the tympanic or mastoid region, or both, and is thought to be an adaptation for more acute hearing and possibly for more delicate balance. Inflation of the tympanic bullae is thought to be a specialization. As the auditory bullae become more inflated, the index increases toward 100.

The Bullar index (width of maxillary arches/breadth across bullae × 100) also expresses the degree of inflation of the auditory bullae. In a generalized mammal, at least in the heteromyids, the index would be 100, but as the auditory bullae become larger the index will decrease from 100.

In attempting to arrange the subspecies of D. ordii according to degree of specialization, the geographic positions of the subspecies have been considered along with the information provided by the above-mentioned indices. These indices were used in the same way as were the indices for the species of the genus. In [Tables 5] and [6] and in the accounts and maps the subspecies are arranged from the least specialized to the most specialized.

TABLE 5

Indices for the Subspecies of DIPODOMYS ORDII

Body Pedal Cranial Bullar

richardsoni 88.85 34.35 60.95 88.25

oklahomae 86.75 35.5 61.7 90.25

compactus 127.7 37.25 59.75 88.35

sennetti 94.25 34.0 62.85 85.95

evexus 80.1 35.7 60.5 92.9

medius 80.4 33.7 63.55 85.9

obscurus 62.95 86.4

terrosus 75.25 35.05 61.6 86.85

fremonti 80.55 34.7 62.9 85.5

uintensis 77.2 35.3 62.3 86.0

monoensis 85.4 36.4 63.4 85.6

ordii 79.05 37.6 62.75 86.9

luteolus 75.0 37.05 62.35 86.3

extractus 83.65 34.35 64.3 84.25

chapmani 75.05 36.35 62.9 85.65

montanus 80.4 36.15 64.25 82.5

cinderensis 85.1 37.2 65.15 84.75

fetosus 81.8 38.85 63.95 83.95

utahensis 80.2 36.95 64.45 84.35

columbianus 78.5 37.55 64.25 84.9

idoneus 72.3 36.6 64.2 85.0

priscus 74.9 39.45 62.3 84.95

celeripes 91.85 38.75 65.0 84.25

cineraceus 75.5 39.1 63.9 84.8

marshalli 81.5 37.3 65.2 83.0

inaquosus 78.05 37.9 64.25 83.05

attenuatus 73.5 37.35 64.0 83.4

fuscus 79.8 39.0 64.3 83.2

longipes 75.7 37.1 64.3 82.75

pallidus 76.9 40.75 64.35 84.65

nexilis 77.1 40.7 64.95 78.45

cupidineus 73.15 39.1 64.1 80.85

palmeri 72.25 37.15 65.1 80.45

TABLE 6

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

Body Pedal Cranial Bullar Average

richardsoni 4 3 3 4 3.5

oklahomae 5 8 5 2 5.0

compactus 1 19 1 3 6.0

sennetti 2 2 10 10 6.0

evexus 15 8 2 1 6.5

medius 12 1 15 11 9.75

obscurus 12 7 10.0

terrosus 25 6 4 6 10.25

fremonti 11 5 12 14 10.5

uintensis 20 7 7 9 10.75

monoensis 6 12 14 13 11.25

ordii 17 23 9 5 13.5

luteolus 27 15 8 8 14.5

extractus 8 4 25 22 14,75

chapmani 26 11 11 12 15.0

montanus 13 10 23 30 19.0

cinderensis 7 18 32 19 19.0

fetosus 9 26 17 24 19.0

utahensis 14 14 28 21 19.25

columbianus 18 22 21 17 19.5

idoneus 31 13 20 15 19.75

priscus 28 30 6 16 20.0

celeripes 3 25 30 23 20.25

cineraceus 24 28 16 18 21.5

marshalli 10 20 33 28 22.75

inaquosus 19 24 22 27 23.0

attenuatus 29 21 18 25 23.25

fuscus 16 27 24 26 23.25

longipes 23 16 26 29 23.5

pallidus 22 32 27 20 25.25

nexilis 21 31 29 33 26.0

cupidineus 30 29 19 31 27.25

palmeri 32 17 31 32 28.0

	Width of rostrum	Length of nasals	Least interorbital width	Nasals Interorbital × 100
terrosus	4.1	14.75	13.5	91.6
luteolus	4.35	13.9	12.95	93.1
evexus	4.3	14.35	13.75	94.8
montanus	4.1	13.5	12.65	93.8
ordii	3.5	13.3	13.0	97.7
idoneus	3.7	13.2	13.75	103.5
palmeri	3.3	12.8	13.0	101.1

	Body	Pedal	Cranial	Bullar
richardsoni	88.85	34.35	60.95	88.25
oklahomae	86.75	35.5	61.7	90.25
compactus	127.7	37.25	59.75	88.35
sennetti	94.25	34.0	62.85	85.95
evexus	80.1	35.7	60.5	92.9

medius	80.4	33.7	63.55	85.9
obscurus			62.95	86.4
terrosus	75.25	35.05	61.6	86.85
fremonti	80.55	34.7	62.9	85.5
uintensis	77.2	35.3	62.3	86.0

monoensis	85.4	36.4	63.4	85.6
ordii	79.05	37.6	62.75	86.9
luteolus	75.0	37.05	62.35	86.3
extractus	83.65	34.35	64.3	84.25
chapmani	75.05	36.35	62.9	85.65

montanus	80.4	36.15	64.25	82.5
cinderensis	85.1	37.2	65.15	84.75
fetosus	81.8	38.85	63.95	83.95
utahensis	80.2	36.95	64.45	84.35
columbianus	78.5	37.55	64.25	84.9

idoneus	72.3	36.6	64.2	85.0
priscus	74.9	39.45	62.3	84.95
celeripes	91.85	38.75	65.0	84.25
cineraceus	75.5	39.1	63.9	84.8
marshalli	81.5	37.3	65.2	83.0

inaquosus	78.05	37.9	64.25	83.05
attenuatus	73.5	37.35	64.0	83.4
fuscus	79.8	39.0	64.3	83.2
longipes	75.7	37.1	64.3	82.75
pallidus	76.9	40.75	64.35	84.65

nexilis	77.1	40.7	64.95	78.45
cupidineus	73.15	39.1	64.1	80.85
palmeri	72.25	37.15	65.1	80.45