The Pocket Gophers (Genus Thomomys) of Utah / University of Kansas Publications, Museum of Natural History, Vol. 1 No. 1

Thomomys bottae aureus Allen

Type.—No. 5243/4123. American Museum of Natural History; Bluff City, San Juan County, Utah; May 12, 1892; collected by Charles P. Rowley (after Allen, type not seen).

Range.—All of San Juan County (except extreme southwestern part) and Grand County east of the Colorado River.

Diagnosis.—Size large (see measurements). Color: Upper parts Cinnamon Buff, lighter on sides; underparts generally white, or if colored at all with only a faint wash of Light Buff; nose and chin blackish gray; top of head blackish due to admixture of black hairs; postauricular patches small and dusky; front feet and hind feet white. Skull: Long, narrow but massive; zygomatic arches not widely spreading, but heavy; jugals thick, union of jugals and zygomatic processes of maxillae thickened; rostrum long but wide; top of rostrum convex in lateral view; ascending processes of premaxillae wide and heavy; nasals thin proximally; braincase long and narrow; tympanic bullae well inflated ventrally; alveolar length of upper molar series long; molars large; pterygoid hamulae heavy; interpterygoid space U-shaped; palate arched; upper incisors long and wide.

Comparisons.—Compared with topotypes of Thomomys bottae osgoodi, aureus differs as follows: Size larger in every measurement taken, except tail which is shorter. Color: Darker throughout except on ventral surface which is lighter. Skull: Larger, longer and wider; nasals longer; rostrum wider and longer; zygomatic arches more nearly straight and heavier; ascending processes of premaxillae wider; basioccipital longer; interpterygoid space U-shaped as opposed to V-shaped; tympanic bullae larger; upper incisors longer, wider; molars larger.

Topotypical specimens of aureus can be distinguished from those of Thomomys bottae dissimilis by: Size larger throughout. Color: A trifle darker on dorsal surface. Skull: Larger in every measurement taken; zygomatic arches heavier and more nearly straight; tympanic bullae larger and more inflated ventrally; interpterygoid space U-shaped as opposed to V-shaped; alveolar length of upper molar series longer; molars larger; upper incisors longer and wider.

Topotypes of aureus differ from those of Thomomys bottae absonus as follows: Size larger in every measurement taken. Color: Darker dorsally, Light Ochraceous as opposed to Cinnamon Buff; due to admixture of gray, absonus has more of a grayish cast. Skull: Larger in every measurement taken, longer, narrower and more compact; zygomatic arches heavier; ascending processes of premaxillae wider; jugals heavier; tympanic bullae larger; interpterygoid space U-shaped rather than V-shaped; upper incisors longer and wider; molars larger.

From topotypes of Thomomys bottae planirostris, aureus can be distinguished as follows: Size larger; tail shorter. Color: Lighter throughout. Skull: Larger in every measurement taken except zygomatic breadth, extension of premaxillae posterior to nasals, and length of upper molariform series which are less; rostrum longer, wider and more convex; nasals slightly arched rather than straight; depression absent rather than present in posterior region of nasals; zygomatic arches not so widely spreading, but equally heavy.

For comparisons with Thomomys bottae alexandrae, see accounts under that form.

Remarks.—Topotypes of aureus are among the largest pocket gophers in the state. They are exceeded in total length only by T. b. lenis and are approached by T. b. aureiventris and T. b. planirostris. On the average they have the longest hind foot, body and ear. The length of the skull is second only to that of lenis as also is the length and breadth of the rostrum relative to the basilar length.

From the time of the original description of aureus in 1893 until 1930, all light colored gophers from Utah were referred to that form. Barnes (1927:100) gives the range of aureus as extending completely across southern Utah and on the west and east sides as far north as central Utah. Since 1930, forms named by E. R. Hall, W. H. Burt, E. A. Goldman and the writer have restricted the range of aureus in Utah to that part of the state east of the Colorado River.

Thomomys bottae birdseyei Goldman

Type.—Male, adult skin and skull, No. 161654. U. S. National Museum (Biological Surveys Collection); Pine Valley Mountains, 5 mi. E Pine Valley, 8,300 ft., Washington County, Utah; April 10, 1909; collected by Clarence Birdseye; original number 861 (after Goldman, type not seen).

Range.—High mountains and plateaus of southwestern Utah.

Diagnosis.—Size medium (see measurements). Color: Upper parts between Cinnamon and Sayal Brown, finely mixed with black in median dorsal region, grading over sides and flanks to Cinnamon on underparts; front feet, hind feet, and distal part of tail white; postauricular patches, chin, cheeks and top of head grayish black. Skull: Depressed along median line of frontals and posterior ends of nasals; region of nasofrontal suture concave ventrally; zygomatic arches heavy and widely spreading, widest posteriorly; posterior ends of nasals straight, tending to be somewhat rounded in some specimens; extension of premaxillae posterior to nasals moderate; tympanic bullae moderately inflated ventrally; basioccipital wide; interpterygoid space widely V-shaped.

Comparisons.—Topotypes of birdseyei differ from near topotypes of Thomomys bottae virgineus, from Beaverdam Wash as follows: Size larger; tail and hind foot longer. Color: Darker throughout, between Cinnamon and Sayal Brown as opposed to Cinnamon Buff. Skull: Larger in every measurement taken except extension of premaxillae posterior to nasals, and length and width of rostrum which are less; skull more depressed in nasofrontal region; zygomatic arches more widely spreading; zygomatic processes of squamosals shorter; pterygoid hamulae longer; tympanic bullae smaller and less inflated ventrally.

Among named races of T. bottae, birdseyei most closely resembles trumbullensis in size, but differs as follows: Hind foot and tail longer. Color: Lighter throughout; postauricular patches smaller and lighter. Skull: Larger; mastoid breadth less; zygomatic arches wider and more widely spreading posteriorly; median frontal depression more marked; extension of premaxillae posterior to nasals greater; tympanic bullae less inflated ventrally; molariform teeth larger.

For comparisons with Thomomys bottae planirostris see account of that form.

Remarks.—T. b. birdseyei is apparently endemic to the mountainous area of southwestern Utah in Washington and Iron counties. It intergrades with virgineus and with planirostris as described in the account of the latter.

Thomomys bottae virgineus Goldman

Type.—Male, adult, skin and skull, No. 262016, U. S. National Museum (Biological Surveys Collection); Beaverdam Creek, near confluence with Virgin River, Littlefield, 1,500 ft., Mohave County, Arizona; October 16, 1936; collected by Luther C. Goldman; original number 67 (after Goldman, type not seen).

Range.—Extreme southwestern Utah, in Beaverdam Wash, Washington County, Utah.

Diagnosis.—Size medium (see measurements). Color: Upper parts Cinnamon Buff, finely mixed with black; sides and flanks Pinkish Buff; underparts Pale Pinkish Buff; front feet, hind feet, and distal part of tail white; nose, cheeks, chin and top of head grayish black. Skull: Robust, with moderately wide zygomatic arches; zygomatic processes of maxillae wide; zygomatic processes of squamosals long; jugals concave laterally, giving the zygomatic arches the appearance of double bowing; nasals long; extension of premaxillae posterior to nasals long; tympanic bullae well inflated ventrally; pterygoid hamulae heavy; interpterygoid space widely V-shaped; molariform teeth large.

Comparisons.—For comparisons of virgineus with Thomomys bottae planirostris and T. b. birdseyei see accounts under those forms.

Topotypical specimens of virgineus can be distinguished from those of Thomomys bottae trumbullensis as follows: Size smaller. Color: Lighter throughout. Skull: Zygomatic arches less widely spreading; jugals more bowed medially; zygomatic processes of squamosals longer; extension of premaxillae posterior to nasals greater; tympanic bullae larger and more inflated ventrally; molariform teeth larger.

Compared with topotypes of Thomomys bottae centralis, virgineus differs in: Size smaller; tail shorter; hind foot smaller. Color: Deeper Cinnamon Buff, thus darker in overall appearance. Skull: Smaller, but relatively wider; zygomatic processes of maxillae heavier; region of maxillo-jugal sutures thicker; jugals more concave laterally; tympanic bullae more inflated ventrally; molariform teeth larger.

Remarks.—This pocket gopher occupies practically the same range in Utah as the large kangaroo rat Dipodomys deserti deserti Stephens. Both are found in the Beaverdam Wash. The type locality of virgineus is but a short distance down the Beaverdam Creek at Littlefield, Arizona. It intergrades with birdseyei, the mountain form to the north and east (see remarks under birdseyei). There are evidences of intergradation with planirostris of the Virgin River Valley above the narrows of the Virgin River where it cuts through the Beaverdam Mountains (see the discussion under planirostris). There are intergradational tendencies exhibited towards centralis in some specimens. Some of the animals are practically indistinguishable in color and there are intergrading cranial characters in the nasals, zygomatic arches and tympanic bullae.

Thomomys bottae planirostris Burt

Type.—Male, adult, skin and skull, No. 8395, Collection of Donald R. Dickey; Zion National Park, Washington County, Utah; May 4, 1920; collected by A. Brazier Howell; original number 2184 (after Burt, type not seen).

Range.—Valley of the Virgin River from Zion National Park west to the Beaverdam Mountains.

Diagnosis.—Size large (see measurements); tail long. Color: Upper parts Sayal Brown; underparts between Vinaceous Cinnamon and Cinnamon, grading to Pinkish Cinnamon in some specimens; nose, chin, cheeks, postauricular patches, and top of head grayish black; front feet and hind feet white; tail Pinkish Buff, with distal third white. Skull: Massive and ridged; nasals straight and flat, simple distally; dorsal surface of rostrum slightly concave at proximal end of nasals; zygomatic arches widely spreading, widest posteriorly; zygomatic processes of maxillae heavy; premaxillae broad and extending far beyond posterior end of nasals; rostrum wide and heavy; palate slightly arched; pterygoid hamulae heavy; interpterygoid space V-shaped; tympanic bullae moderately inflated ventrally, somewhat compressed laterally; upper incisors long and heavy; molariform teeth large.

Comparisons.—Compared with topotypes of Thomomys bottae birdseyei, planirostris differs as follows: Size larger, except total length which averages slightly less in females. Color: Lighter throughout. Skull: Larger in every measurement taken; more massive; rostrum wider, longer and more nearly flat; nasals straight and not inflated dorsally on distal end; premaxillae wider at posterior ends; extension of premaxillae posterior to nasals greater; zygomatic arches heavier, especially the zygomatic processes of the maxillae; posterior ends of nasals more nearly truncate as opposed to generally rounded; tympanic bullae more nearly flat and relatively smaller; upper incisors longer and heavier; interpterygoid space more narrowly V-shaped; molariform teeth much heavier.

Topotypes of planirostris differ from near topotypes of Thomomys bottae virgineus as follows: Size larger; tail and hind foot longer. Color: Slightly darker dorsally, but markedly darker ventrally; postauricular patches smaller and lighter. Skull: Larger in every measurement taken; skull more massive; nasals flat, neither arched nor swollen distally; rostrum wider; nasofrontal region flattened or concave as opposed to convex; premaxillae relatively narrower; zygomatic arches heavier, especially in the processes of the maxillae; tympanic bullae smaller and less inflated ventrally; interpterygoid space generally more narrowly V-shaped; upper incisors longer and heavier; molariform teeth larger.

From topotypes of Thomomys bottae trumbullensis, planirostris differs in: Size larger throughout; tail longer. Color: Much lighter throughout. Skull: More convex dorsally; rostrum wider and more depressed distally; extension of premaxillae posterior to nasals greater; zygomatic arches shorter, and not as widely spreading posteriorly; interpterygoid space more narrowly V-shaped; tympanic bullae smaller; upper incisors wider and longer; molariform teeth larger.

Topotypes of planirostris can be easily distinguished from those of Thomomys bottae absonus by darker color throughout and markedly larger size.

Remarks.—From the synonomy at the beginning of this account one may note that the animals here ascribed to this subspecies have had nearly as many subspecific names applied to them as there have been investigators who have written about them. Although each of the previous writers had but a small amount of material upon which to base his opinion, the diversity of opinion as to subspecific status bespeaks the instability of these animals. The present study is based upon eighty animals including additional comparative material.

All animals from Zion National Park have the characters pointed out by Burt (1931:38) in his description of this form. Farther down the Virgin River Valley towards St. George, however, some very perplexing problems of intergradation are encountered. St. George and environs may correctly be thought of as a "melting pot." Each of the fifty-seven animals studied from this region is an intergrade; some specimens combine the characters of three subspecies.

As may be seen on the distribution map, three different subspecies of Thomomys bottae occur in Washington County. Down the river, below St. George, the race virgineus inhabits the Virgin River Valley below the narrows of the Beaverdam Mountains. Because these narrows are filled with water from wall to wall during periods of high runoff, they form an effective barrier at present to migration of pocket gophers. The mountains to the north of St. George are inhabited by the dark form, birdseyei. The type locality of planirostris is on the middle reaches of the Virgin River, in Zion National Park. In addition Mount Trumbull to the south, in northern Arizona, is the locality of another subspecies, trumbullensis.

Unquestionably the easiest route of migration into the St. George area is down the Virgin River from Zion National Park; no barrier to gophers occurs between the Park and St. George. Although the animals from St. George are all intergrades, the majority of their affinities as would be expected are with planirostris from Zion National Park. The river itself is not an impassable barrier for gophers to the north and south of it, since this stream frequently changes its course, and often nearly dries up. The Virgin River Valley in Zion National Park is in the bottom of a relatively deep, narrow canyon which has sheer rock escarpments. The upper reaches of the river are inhabited by pocket gophers of another species, Thomomys talpoides.

Two specimens from St. George, north of the Virgin River, were identified as centralis by Hall and Davis (1934:52), but were stated to be intergrades between centralis, trumbullensis and planirostris. Goldman (1938:338) referred twelve specimens from St. George to nicholi, but stated that they intergraded with planirostris. Twenty-six other specimens from three miles southwest of St. George on the west side of Santa Clara Creek, about one-half mile above its confluence with the Virgin River and on its north side, like the topotypes of planirostris were taken in May and have complete, fresh summer pelage. With the exception of two specimens which show the ventral color of virgineus, these animals are indistinguishable in color from the topotypes of planirostris. A study of eleven measurements of the males of this series yield the following data: Like planirostris in four measurements, birdseyei in one, virgineus in one; intergrade between planirostris and birdseyei in two, planirostris and virgineus in two and birdseyei and virgineus in one. Corresponding measurements of the females show the animals to be: Like planirostris in four measurements, birdseyei in one, virgineus in two; intergrade between planirostris and birdseyei in two, planirostris and virgineus in one and birdseyei and virgineus in one. In eight of eleven measurements the males either are like planirostris or intergrade towards it, and the females are similarly allied to planirostris in seven out of eleven measurements. In none of the measurements was either sex referable to trumbullensis.

Intergradation was noted in still other cranial details. In the heavy, relatively straight zygomatic arches, a majority of the skulls resemble those of planirostris, although some show the elongated zygomatic processes of the squamosals that are characteristic of virgineus. Some skulls show a tendency toward birdseyei in the widely spreading posterior regions of the zygomatic arches. The nasals for the most part are as in planirostris. Intergradation between all three subspecies is shown in the extension of the premaxillae posterior to the nasals. Some skulls show the lateral concavity of the jugals which is characteristic of virgineus. The tympanic bullae are variable but on the average are intermediate between those of planirostris and birdseyei, but more as in the latter. The size of the pterygoid hamulae is like that of planirostris, but the shape of the interpterygoid space is more like that of birdseyei. The size of the molariform teeth is as in birdseyei. The incisors are intermediate between those of planirostris and birdseyei, but more like those of birdseyei.

Eighteen specimens from St. George and its environs, on the north side of the Virgin River, agree with the twenty-six specimens just described, except that they show more evidence of intergradation with birdseyei in slightly darker color, length of hind foot, length of nasals and alveolar length of the upper molar series.

One specimen from three miles south, two from two miles southwest, another from four miles southeast of St. George, and four immature animals from Short Creek Road south of the town of Virgin, all on the south side of the Virgin River, are darker than topotypes of planirostris and show intergradation with trumbullensis to the south. In size they are likewise closer to the latter race. They intergrade with trumbullensis in the size and shape of the zygomatic arches and tympanic bullae. In the majority of cranial details, however, they are like planirostris to which they are here referred.

One specimen, a skin only, from Danish Ranch, 5 miles northwest of Leeds, north of the Virgin River is an intergrade in size and color between birdseyei and planirostris, but referable to the latter.

Three specimens from the East Entrance, and three from near the east entrance to Zion National Park are much darker than topotypes of planirostris. All of these animals are in worn pelage, thus allowing a great amount of the black underfur to show, which gives a markedly darker color. The unworn hair is only slightly darker than that of the topotypes. The cranial details prove these animals to be intergrades between planirostris and trumbullensis. They resemble trumbullensis in size of tympanic bullae, extension of the premaxillae posterior to the nasals and shape of the nasals. The majority of the cranial details are as in planirostris to which they are here referred.

When Goldman (1938:337) named Thomomys bottae nicholi from northern Arizona he referred twelve specimens from St. George, Washington County, Utah, to his newly named race. He noted that the animals from this region intergrade with planirostris. I have had occasion to study one-fourth of the material available to Goldman for his original description of nicholi. For his specimens listed as from St. George, the exact locality of capture, which is so essential in this distributional study, was not given. All of the specimens that I have seen from the Biological Surveys Collection are from the south side of the Virgin River, while St. George itself is on the north side. As noted earlier in this account there are differences between the gophers from the two sides of the Virgin River in this area. Those from the north side are intergrades between birdseyei, planirostris and virgineus, while those from the south side are intergrades between planirostris and trumbullensis.

Goldman (loc. cit.) mentioned several times that the skulls of nicholi were nearly indistinguishable from, or closely resembled those of, trumbullensis. Color was the only truly diagnostic character mentioned by Goldman. My study reveals the same differences and likenesses found by Goldman, but I consider color alone insufficient basis in this instance for establishing a new subspecies, and regard Thomomys bottae nicholi as a synonym of the earlier proposed name, Thomomys bottae trumbullensis.

The animals from the south side of the Virgin River, labelled as from St. George, Washington County, heretofore referred by Goldman to nicholi, are intergrades between trumbullensis and planirostris and along with other specimens from the same place are referable to the latter race.

Thomomys bottae absonus Goldman

Type.—Male, adult, skin and skull, No. 250016, U. S. National Museum (Biological Surveys Collection); Jacobs Pools, Houserock Valley, 4,000 ft., Coconino County, Arizona; June 7, 1931; collected by E. A. Goldman; original number 23569 (after Goldman, type not seen).

Range.—Southern Utah in Kane and Garfield counties, in the drainages of Kanab Creek, Johnson Creek, Paria River and Escalante River.

Diagnosis.—Size medium (see measurements). Color: Upper parts Ochraceous Buff mixed with dusky; sides and underparts Light Ochraceous Buff; chin, nose, cheeks and top of head grayish black; postauricular patches black mixed with buff; front feet, hind feet, inguinal region and distal third of tail white. Skull: Nasals relatively long; rostrum narrow; ascending processes of premaxillae narrow; extension of premaxillae posterior to nasals short; lambdoidal and sagittal crests poorly developed; zygomatic arches light; jugals nearly straight; palate narrow; molariform teeth small.

Comparisons.—Compared with topotypes of Thomomys bottae trumbullensis, absonus differs in: Size smaller. Color: Markedly lighter throughout. Skull: Smoother, less angular; zygomatic arches weak as opposed to robust; nasals more convex as viewed laterally; extension of premaxillae posterior to nasals less; ascending processes of premaxillae narrower; palate narrower; palatal pits shallower; rostrum narrower; molariform teeth smaller.

For comparisons of absonus with Thomomys bottae aureus see account under that form.

Among named races of Thomomys bottae, absonus most closely resembles planirostris, but can be distinguished from the topotypes as follows: Size markedly smaller. Color: Lighter, more buffy throughout. Skull: Smaller, less ridged and more nearly flat; nasals convex as opposed to flat; extension of premaxillae posterior to nasals less; width of ascending processes of premaxillae less; zygomatic arches weaker; palate narrower; alveolar length of upper molar series shorter; tympanic bullae more inflated ventrally; molariform teeth smaller and lighter.

Remarks.—One specimen from Kanab is an intergrade between trumbullensis and absonus. The majority of its characters are with absonus to which it is referred (see Hall and Davis, 1934:52). Two specimens from Escalante are intergrades between absonus and dissimilis, but are referable to absonus.

Thomomys bottae alexandrae Goldman

Type.—Male, adult, skin and skull, No. 250969, U. S. National Museum (Biological Surveys Collection); 5 mi. SE Rainbow Lodge, near Navajo Mountain, Coconino County, Arizona; June 16, 1933; collected by E. A. Goldman; original number 23613 (after Goldman, type not seen).

Range.—In extreme southwestern San Juan County, Utah. Known only from Navajo Mountain, probably limited to the area enclosed on the north by the Colorado and San Juan rivers, on the east and west by Navajo and Piute canyons, respectively.

Diagnosis.—Size small (see measurements). Color: Upper parts Cinnamon Buff, grading over the sides to Pinkish Buff on underparts; nose and top of head grayish black; hind feet and tail white; postauricular patches large and dark. Skull: Small and not heavily ridged; zygomatic arches widely spreading but weak; zygomatic arches nearly parallel; tympanic bullae moderately inflated ventrally; palate not arched; interpterygoid space U-shaped; dentition light.

Comparisons.—Compared to topotypes of Thomomys bottae absonus, alexandrae differs as follows: Size smaller in every measurement taken. Color: Upper parts Cinnamon Buff as contrasted with Light Ochraceous Buff. Skull: Smaller in every measurement taken except interorbital breadth and alveolar length of upper molar series which are larger; molariform teeth larger.

Among named races of Thomomys bottae occurring in Utah, alexandrae most resembles T. b. aureus to the northeast. It can be distinguished from topotypes of the latter by: Size smaller in every measurement taken. Color: Darker throughout. Skull: Smaller, slenderer and more nearly flat; palate nearly flat as opposed to arched; zygomatic arches weaker and not so widely spreading; interparietal narrower; tympanic bullae smaller; dentition weaker.

Remarks.—Goldman (1933:464) accorded alexandrae full specific status, because he found no intergradation with other races, from which he thought alexandrae had been isolated perhaps for thousands of years by the barriers of the surrounding terrain. Benson (1935:450) noted resemblances between alexandrae and specimens of latirostris from Keams Canyon, Zuni Well, and Winslow in Navajo County, Arizona (= aureus), and also between alexandrae and absonus from Houserock Valley, Arizona. He thought that alexandrae is no more differentiated or isolated than each of several other kinds of desert pocket gophers, and, therefore, accorded alexandrae only subspecific status, as I, also, am inclined to do.

Measurements of Adult Males of Thomomys

(In millimeters)

Measurements of Adult Males of Thomomys—Continued

Measurements of Adult Males of Thomomys—Concluded