Taxonomy of the Chipmunks, Eutamias quadrivittatus and Eutamias umbrinus Part 3

_Skull_: Large, with strong zygomata; braincase well inflated. _Baculum_: As in _E. u. umbrinus_.

_Comparisons._--From _E. u. umbrinus_, the subspecies from the Uinta and northern Wasatch Mountains in Utah, _E. u.

fremonti_ differs in: Sides darker; antiplantar surfaces of feet darker; postauricular patch grayer; crown more grayish; skull slightly larger.

From _E. ruficaudus ruficaudus_, the species and subspecies from western Montana, _E. u. fremonti_ differs in: General tone of upper parts, sides, underside of tail, and feet, all darker in coloration; baculum shorter and proportionally twice as wide at base.

For comparison with _E. u. monta.n.u.s_, see the account of that subspecies.

_Remarks._--The geographic ranges of _E. umbrinus fremonti_ and _E. ruficaudus ruficaudus_ are allopatric and no specimens have ever been taken in the intermediate area to indicate whether or not these two species anywhere occur together. The bacula in the two species differ to the same degree as those of _E. quadrivittatus_ and _E. umbrinus_. The differences between _E. u. fremonti_ and _E. r.

ruficaudus_ are such that in my opinion, _E. ruficaudus_ is a distinct species.

_Specimens examined._--Total number, 58.

=Montana=: _Park Co._: Beartooth Mountains, 2 BS.

=Idaho=: _Bonneville Co._: Big Hole Mountains, 9,000 ft., near Irwin, 1 BS.

=Wyoming=: _Yellowstone Park_, 2. Park Co.: 16-1/4 mi. N and 17 mi. W Cody, 5,625 ft., 2. _Teton Co._: 1 mi. E and 1/4 mi.

N Togwotee Pa.s.s, 9,800 ft., 2; Amphitheatre Lake, Teton Park, 1 MM; Flat Creek, 4 MM; head of Cache Creek, 4 MM; Jackson, Upper Arizona Creek, 2 MM; Flat Creek-Granite Creek divide, 6 MM; Flat Creek Pa.s.s, 1 MM; Flat Creek-Gravel Creek divide, 2 MM. _Lincoln Co._: La Barge Creek, 9,000 ft., 2 BS. _Fremont Co._: Togwotee Pa.s.s, 12; 12 mi. N and 3 mi. W Shoshoni, 4,650 ft., 1; Mosquito Park R. S., 9,500 ft., 17-1/2 mi. W and 2-1/2 mi. N Lander, 1; 17 mi. S and 6-1/2 mi. W Lander, 8,450 ft., 3. _Sublette Co._: 31 mi. N Pinedale, 8,025 ft., 2; W side Barbara Lake, 10,300 ft., 8 mi. S and 3 mi. W Fremont Peak, 4; 19 mi. W and 2 mi. S Big Piney, 7,700 ft., 5.

=Eutamias umbrinus monta.n.u.s= new subspecies

_Type._--Male, adult, skull, skin, and baculum, No. 20105 Univ. Kansas Mus. Nat. Hist.; from 1/2 mi. E and 3 mi. S Ward, 9,400 ft., Boulder County, Colorado; obtained on August 1, 1947, by E. L. c.o.c.krum; original No. 721.

_Diagnosis._--Size large; sides Clay Color; antipalmar and antiplantar surfaces of feet Cinnamon-Buff; baculum as in E.

u. umbrinus.

_Description._--_Color pattern_: Crown Raw Sienna mixed with gray; upper facial stripe and ocular stripe black mixed with Sepia; submalar stripe Snuff Brown mixed with black; ear black or Sepia, anterior margin Ochraceous-Tawny, posterior margin and postauricular patch grayish white; hairs inside posterior part of pinna Cinnamon-Buff; median dorsal dark stripe black with Sayal Brown along margins; lateral dark stripes black mixed with Sayal Brown; outermost dorsal dark stripes obsolete, Sayal Brown mixed with black; median pair of dorsal light stripes Pale Smoke Gray mixed with Clay Color; outer pair of dorsal light stripes creamy white; sides Clay Color; rump and thighs Neutral Gray; dorsal surface of tail black mixed with Cinnamon-Buff; ventral surface of tail Ochraceous-Tawny; hairs around margin of tail Cinnamon-Buff or Ochraceous-Tawny; antipalmar and antiplantar surfaces of feet Cinnamon-Buff; underparts creamy white with dark underfur. _Skull_: Large; zygomata strong; braincase well inflated. _Baculum_: As in _E. u. umbrinus_.

_Comparisons._--From _E. quadrivittatus quadrivittatus_, the subspecies and species to the south, _E. u. monta.n.u.s_ differs in: General tone of upper parts darker; braincase significantly narrower; baculum shorter and markedly wider at base.

From _E. u. umbrinus_, the subspecies from the Uinta and northern Wasatch Mountains, _E. u. monta.n.u.s_ differs in: General tone of upper parts brighter (less tawny); sides more tawny; skull slightly larger.

From _E. u. sedulus_, the subspecies from the Henry Mountains of Utah, _E. u. monta.n.u.s_ differs in: Sides darker; general tone of upper parts darker.

From _E. u. fremonti_, the subspecies from the mountains of western and northwestern Wyoming, _E. u. monta.n.u.s_ differs in: General tone of upper parts lighter; hairs around outermost edge of tail tawnier.

_Remarks._--Howell (1929:83) stated that the specimens of _E.

quadrivittatus quadrivittatus_ (= _E. umbrinus monta.n.u.s_) from Estes Park, Long's Peak, and Gold Hill, all in Colorado, "average somewhat darker on the back and sides than typical _quadrivittatus_; the light dorsal stripes are also somewhat duller and the dark stripes less blackish, thus showing an approach to the characters of _umbrinus_."

Now there are more specimens of _E. u. monta.n.u.s_ from the mountains of north-central Colorado than were available to Howell. He was not aware of the striking difference between the bacula of _E. quadrivittatus_ and _E. umbrinus_, and the constancy of this difference between all the subspecies of one species and those of the other.

Although the geographic range of _E. u. umbrinus_ is closer to the ranges of _E. u. fremonti_ and _E. u. monta.n.u.s_ than to the geographic range of _E. u. adsitus_, _E. u. umbrinus_ seems to be more closely related to _E. u. adsitus_ than to _E. u. fremonti_ or _E. u.

monta.n.u.s_. This observation may be explained by the presence of continuous habitat for _E. umbrinus_ between the ranges of _E. u.

umbrinus_ and _E. u. adsitus_, whereas _E. u. fremonti_ and _E. u.

monta.n.u.s_ are each separated from _E. u. umbrinus_ by areas unsuitable for occupancy by _E. umbrinus_. It must be noted, however, that no actual intergrades between _E. u. umbrinus_ and _E. u. adsitus_ are known.

_Specimens examined._--Total number, 36.

=Wyoming=: _Albany Co._: 3 mi. ESE Brown's Peak, 10,000 ft., 2; 3-1/2 mi. S Wood's Landing, 1.

=Utah=: _Uintah Co._: PR Springs, 7,950 ft., 43 mi. S Ouray, Uintah-Grand county line, 1 UU.

=Colorado=: _Jackson Co._: Mount Zirkel, 10,000 ft., on trail, 2 WC; Buffalo Pa.s.s, 10,380 ft., 1 WC; Buffalo Pa.s.s road, 10,130 ft., 1 WC. _Larimer Co._: 2 mi. E Log Cabin, 7,450 ft., 1 WC; Estes Park, 7,600 ft., 1; 1-1/2 mi. SW Estes Park, 1; 2-1/2 mi. SW Estes Park, 2; 3-1/2 mi. SW Estes Park, 1; 12 mi. SW Estes Park, 1. _Rio Blanco Co._: 1 mi. NW PaG.o.da Peak, 10,400 ft., 1. _Boulder Co._: Long's Peak, 7 BS; 1 mi.

NE Ward, 10,000 ft., 1; 3 mi. S Ward, 9,000 ft., 5; 1/2 mi. E and 3 mi. S Ward, 9,400 ft., 1; 1 mi. S Gold Hill, 8,200 ft., 1. _Clear Creek Co._: Davidson Mine, 3 mi. SW Idaho Springs, 1; Georgetown, 1 CM. _Jefferson Co._: Silver Plume, 1 CM.

_Park Co._: Tarryall Creek Camp, 8,700 ft., 1 WC. _Gunnison Co._: S side Crested b.u.t.te Mountain, 9,500 ft., 1 WC; mouth of Virginia Basin, Gothic, 1 FC.

DISCUSSION

The chipmunks that heretofore have been a.s.signed to the species _Eutamias quadrivittatus_ are here a.s.signed to two species, _E.

quadrivittatus_ and _E. umbrinus,_ for the following reasons:

1. The baculum of _E. quadrivittatus_ differs from that of _E.

umbrinus_ in having a narrow base (see figs. 3, 4). This difference permits any specimen which has an a.s.sociated baculum to be readily identified to species.

2. The cranial breadth in the subspecies of _E. quadrivittatus_ is significantly larger than in the subspecies of _E. umbrinus_.

3. Specimens of _E. umbrinus_ are darker than any specimen of _E.

quadrivittatus_.

4. Where the geographic ranges of _E. quadrivittatus_ and _E.

umbrinus_ come close to one another (probably they meet at some places), _E. umbrinus_ occupies a higher position in terms of life-zones. Wherever either of these two species, but not the other, occurs on a mountain the species occupies both the higher and lower life-zones.

[Ill.u.s.tration: FIGS. 3 and 4. Baculum of _Eutamias quadrivittatus quadrivittatus_, No. 35648/47919 BS; from Canon City, Fremont Co., Colorado. Figure 3, lateral view of right side; figure 4, dorsal view.

FIG. 5. Baculum of _Eutamias umbrinus umbrinus_, No. 38062; from Paradise Park, 21 mi. W and 15 mi. N Vernal, 10,050 ft., Uintah Co., Utah. Lateral view of right side.

FIG. 6. Baculum of _Eutamias umbrinus monta.n.u.s_, No. 20105; from 1/2 mi. E and 3 mi. S Ward, 9,400 ft., Boulder Co., Colorado. Dorsal view.]

The differences between _E. quadrivittatus_ and _E. umbrinus_ are as great as, or greater than, between many species of chipmunks, such as between _E. minimus_ and _E. amoenus_, and between _E. quadrivittatus_ and _E. cinereicollis_.

Although I know of no ecological differences between _E. umbrinus_ and _E. ruficaudus_, the morphological differences, as for example, differences in the structure of the baculum, and differences in color pattern, lead me to maintain _E. ruficaudus_ and _E. umbrinus_ as separate species.

The present distribution of these two species is attributable to the uplift of the Rocky Mountains in the Pleistocene. That the uplift of the Rocky Mountains and the erosion which produced the present-day relief took place in Pleistocene times is supported by the evidence found by several geologists such as Hunt and Sokoloff (1950:109-123).

The present geographic distribution of _E. umbrinus_ and _E.

quadrivittatus_ conceivably came about as follows: _E. umbrinus_-like chipmunks were present, before the uplift of the major chains of mountains, on isolated, low mountain ranges that were not covered with glaciers (such as the laccolithic mountains that occur in Utah) in Pleistocene time, while _E. quadrivittatus_-like chipmunks were present in the central parts of New Mexico, Colorado, and southern Wyoming. With the advent of uplift, the habitats in the central parts of these states were changed from a plains-like habitat to a habitat that resembled the forest habitats that exist today.

_E. umbrinus_-like chipmunks then invaded this newly formed habitat and displaced any _E. quadrivittatus_-like chipmunks that were less well adapted to live there. The Colorado River probably served as a barrier that kept the _E. umbrinus_-like chipmunks and _E.

quadrivittatus_-like chipmunks separated up to this time. Invasion of the new forest-niche by _E. umbrinus_-like chipmunks may have taken place through the Uinta Mountains of northeastern Utah, after the glaciers disappeared from these mountains, since the Colorado River probably prevented any eastward migration farther south.