Part 6

Remarks.--Howell (1929:83) stated that the specimens of E. quadrivittatus quadrivittatus (= E. umbrinus montanus) 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. montanus 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. montanus 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. montanus. 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. montanus 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 Pass, 10,380 ft., 1 WC; Buffalo Pass 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 Pagoda 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 Butte Mountain, 9,500 ft., 1 WC; mouth of Virginia Basin, Gothic, 1 FC.

DISCUSSION

The chipmunks that heretofore have been assigned to the species Eutamias quadrivittatus are here assigned 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 associated 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.

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 montanus, 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.

TABLE 1

Average and Extreme Measurements in Millimeters of Adult Eutamias quadrivittatus and E. umbrinus

KEY A: Greatest length of skull B: Zygomatic breadth C: Cranial breadth D: Length of nasals E: Total length F: Length of tail G: Length of lower tooth-row H: Condylo-alveolar length of mandible

====================================================================== | A | B | C | D | E | F | G | H -------------+------+------+------+------+-----+-------+------+------- | | E. q. quadrivittatus, Canon City, Fremont Co., | Colorado. | Mean (7) | 35.7 | 19.3 | 16.2 | 11.0 | 222 | 99.4 | 5.40 | 18.98 Min | 35.7 | 19.1 | 15.9 | 10.6 | 216 | 93.0 | 5.32 | 18.65 Max | 35.8 | 19.8 | 16.5 | 11.6 | 230 | 104.0 | 5.49 | 19.41 | | | | | | | | Mean (3) | 35.9 | 19.9 | 16.5 | 10.9 | 231 | 99.0 | 5.42 | 19.10 Min [Female] | 35.6 | 19.9 | 16.5 | 10.7 | 200 | 98.0 | 5.39 | 18.85 Max | 36.2 | 19.9 | 16.6 | 11.2 | 232 | 100.0 | 5.49 | 19.28 | | | | | | | | +------+------+------+------+-----+-------+------+------- | | E. q. hopiensis, Moab, Grand Co., Utah. | Mean (11) | 34.4 | 19.4 | 16.3 | 10.0 | 212 | 90.7 | 5.19 | 18.36 Min | 33.5 | 19.2 | 15.9 | 9.3 | 208 | 85.0 | 4.92 | 17.80 Max | 35.4 | 20.0 | 16.8 | 10.5 | 220 | 96.0 | 5.38 | 18.96 | | | | | | | | Mean (5) | 34.9 | 19.6 | 16.4 | 10.5 | 219 | 94.4 | 5.16 | 18.58 Min [Female] | 34.2 | 19.3 | 15.9 | 10.1 | 210 | 85.0 | 5.13 | 18.00 Max | 35.7 | 20.1 | 16.6 | 10.7 | 228 | 104.0 | 5.20 | 19.19 | | | | | | | | +------+------+------+------+-----+-------+------+------- | | E. u. umbrinus, Mts. S Robertson, Uintah Co., | Wyoming. | Mean (11) | 34.7 | 18.9 | 15.7 | 10.9 | 218 | 96.2 | 5.13 | 18.04 Min | 34.3 | 18.3 | 15.6 | 10.3 | 215 | 81.0 | 4.79 | 17.57 Max | 35.2 | 19.4 | 16.0 | 11.7 | 228 | 112.0 | 5.42 | 18.59 | | | | | | | | Mean (4) | 35.1 | 19.2 | 15.9 | 11.0 | 224 | 96.4 | 5.17 | 18.46 Min [Female] | 34.9 | 18.6 | 15.7 | 10.3 | 204 | 90.0 | 5.11 | 18.31 Max | 35.4 | 20.0 | 16.2 | 11.8 | 234 | 100.0 | 5.22 | 18.98 | | | | | | | | +------+------+------+------+-----+-------+------+------- | | E. u. adsitus, Britts Meadow, Beaver Co., Utah. | Mean (6) | 34.8 | 18.9 | 15.5 | 10.8 | 214 | 89.6 | 5.16 | 18.07 Min | 34.3 | 18.5 | 15.3 | 10.4 | 203 | 73.0 | 4.64 | 17.69 Max | 35.4 | 19.6 | 16.1 | 11.3 | 225 | 95.0 | 5.34 | 18.70 | | | | | | | | Mean (6) | 35.1 | 19.5 | 16.0 | 11.0 | 228 | 96.5 | 5.11 | 18.75 Min [Female] | 33.9 | 18.9 | 15.9 | 10.6 | 215 | 95.0 | 5.00 | 18.51 Max | 36.2 | 20.0 | 16.3 | 11.8 | 233 | 98.0 | 5.33 | 19.40 | +------+------+------+------+-----+-------+------+------- | | E. u. sedulus, Mt. Ellen, Henry Mts., Garfield Co., | Utah. | Mean (5) | 34.7 | 18.7 | 15.6 | 10.7 | 218 | 93.0 | 5.21 | 18.74 Min | 33.5 | 18.4 | 15.4 | 10.1 | 213 | 89.0 | 5.09 | 18.48 Max | 35.5 | 19.1 | 15.9 | 11.2 | 224 | 97.0 | 5.28 | 19.38 | | | | | | | | Mean (2) | 34.9 | 19.4 | 16.1 | 11.1 | 227 | 98.0 | 5.24 | 18.74 Min [Female] | 34.9 | 19.3 | 16.1 | 11.0 | 224 | 96.0 | 5.07 | 19.24 Max | 34.9 | 19.5 | 16.1 | 11.3 | 231 | 100.0 | 5.42 | 19.80 | | | | | | | | +------+------+------+------+-----+-------+------+------- | | E. u. inyoensis, Ruby Mts., Elko and White Pine | Cos., Nev. | Mean (12) | 34.4 | 19.0 | 15.7 | 10.5 | 208 | 89.5 | 5.15 | 18.12 Min | 33.5 | 18.6 | 15.2 | 10.0 | 196 | 85.0 | 5.01 | 17.32 Max | 35.4 | 19.6 | 16.1 | 11.5 | 220 | 100.0 | 5.37 | 18.81 | | | | | | | | Mean (5) | 34.9 | 19.4 | 15.7 | 10.5 | 215 | 92.8 | 5.19 | 18.63 Min [Female] | 34.4 | 19.1 | 15.4 | 10.4 | 204 | 86.0 | 5.04 | 18.50 Max | 35.2 | 19.7 | 16.0 | 10.7 | 226 | 102.0 | 5.33 | 18.80 | | | | | | | | +------+------+------+------+-----+-------+------+------- | | E. u. nevadensis, Measurements of the type | (Burt 1931:300). | | 34.8 | 19.3 | 16.2 | 11.0 | 205 | 89.0 | ... | ... | | | | | | | | +------+------+------+------+-----+-------+------+------- | | E. u. fremonti, Togwotee Pass, Fremont Co., Wyoming. | Mean (8) | 35.6 | 19.3 | 15.9 | 11.4 | 223 | 99.0 | 5.34 | 19.17 Min | 35.2 | 18.9 | 15.8 | 11.1 | 216 | 95.0 | 5.22 | 18.72 Max | 36.5 | 19.7 | 16.1 | 11.8 | 243 | 111.0 | 5.57 | 19.78 | | | | | | | | Mean (6) | 35.3 | 19.6 | 15.9 | 11.3 | 229 | 101.0 | 5.40 | 19.02 Min [Female] | 34.5 | 19.3 | 15.7 | 10.9 | 223 | 92.0 | 5.35 | 18.37 Max | 36.0 | 20.0 | 16.5 | 12.0 | 239 | 110.0 | 5.44 | 19.51 | | | | | | | | +------+------+------+------+-----+-------+------+------- | | E. u. montanus, Boulder Co., Colorado. | Mean (5) | 35.2 | 18.8 | 15.5 | 10.8 | 226 | 96.0 | 5.20 | 18.29 Min | 34.7 | 18.4 | 15.2 | 10.1 | 215 | 93.0 | 5.03 | 17.80 Max | 36.8 | 19.4 | 16.2 | 11.5 | 232 | 115.0 | 5.53 | 19.36 | | | | | | | | Mean (6) | 35.7 | 19.1 | 15.6 | 10.9 | 226 | 98.0 | 5.28 | 18.67 Min [Female] | 35.1 | 18.8 | 15.1 | 10.3 | 215 | 89.0 | 5.06 | 18.09 Max | 36.5 | 19.5 | 16.0 | 11.6 | 231 | 105.0 | 5.58 | 19.35 | | | | | | | | -------------+------+------+------+------+-----+-------+------+-------

LITERATURE CITED

BENSON, S. B. 1935. A biological reconnaissance of Navajo Mountain, Utah. Univ. California Publ. Zool., 40:439-455, December 31.

BURT, W. H. 1931. Three new subspecies of chipmunks of the genus Eutamias from Nevada. Jour. Mamm., 12:298-301, August 24.

DURRANT, S. D. 1952. Mammals of Utah, taxonomy and distribution. Univ. Kansas Publ. Mus. Nat. Hist., 6:1-549, 91 figs., 30 tables, August 10.

HALL, E. R. 1946. Mammals of Nevada. Univ. California Press, Berkeley, California, pp. xi + 710, 11 pls., 485 figs., July 1.

HARDY, R. 1945. The taxonomic status of some chipmunks of the genus Eutamias in southwestern Utah. Proc. Biol. Soc. Washington, 58:85-87, June 30.