John A. White

“ This relationship can be seen clearly in the structure of the malleus, baculum, hyoid apparatus, hyoid musculature, the presence or absence of P3, the projection of the anterior root of P4 in relation to the masseteric knob, and in the color pattern.
Because the genera Eutamias and Tamias occupy similar ecological niches, the structural similarities that permit these animals to be called chipmunks, show convergence, and thus can be assumed to be adaptive. ”

“ The differences in anatomy and color between many species of chipmunks are subtle, and refined techniques are required to discover them. When "measuring" chipmunks taxonomically, it is necessary to use a "chipmunk scale" and not, for example, a "pocket-gopher scale." In explanation, some species of pocket gophers closely allied to each other, and even some subspecies of the same species, differ markedly in color and in size and shape of parts of the skeleton; comparable differences are not so pronounced among many species of chipmunks. ”

“ Eutamias sonomae Grinnell
Figure 4
Upper parts rich reddish, more or less dulled by gray; backs of pinnae of ears nearly bare; tail long and bushy; size large; skull large, long, and narrow; rostrum deep.
Baculum: Shaft thin; keel low, 1/10 of length of tip; tip 27 to 31 per cent of length of shaft; angle formed by tip and shaft 130°; distal 1/4 of shaft slightly compressed laterally; base deeper and wider than shaft; shaft of medium length, 3.03 to 3.30 mm.; ridges on either side of tip strongly developed, partly obscuring keel from side. ”

“ Dorsal dark stripes distinct and usually blackish; skull smaller; tip of baculum of adults less than 28 per cent of length of shaft.
Remarks.—This is the smallest of the species of chipmunks in Wyoming, and in the state can be readily distinguished from the other species by the smaller size and by the characteristic proportions of the baculum.
E. minimus occurs in all the Life-zones of Wyoming, and inhabits open country, such as in the great expanses where sagebrush (Artemesia sp.) is predominant, or inhabits the edges of forests, never occurring in the forest proper. ”

“ 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. ”

“ This "silken hair" is replaced by adult summer pelage, and juvenal chipmunks which are molting into adult summer pelage closely resemble the adult males, and later on in the summer, the adult females. Adult females molt later, as a rule, than adult males probably because of lactation. Summer molt begins, on chipmunks in Wyoming and South Dakota, in the latter part of June and is completed by the latter part of August or the first part of September. ”

“ Thus the bacula that were borrowed from the University of Michigan, are maintained there in a separate collection, whereas the bacula borrowed from other museums and those that are at the University of Kansas, Museum of Natural History, are housed with the skulls of the corresponding specimens. ”

“ In Sangamonian time, E. minimus-like chipmunks occurred over most of the region which is now Wyoming, and were divided into two size-groups, much as E. minimus is today.
When permanent snow fields were formed in Wisconsinan time, these chipmunks were restricted in their ranges, not, of course, occurring on the glaciers.
When the glaciers melted at the end of Wisconsinan time, new habitats were thus "uncovered." The chipmunks which moved into these ice-free areas, then, became adapted to the new habitats. This then accounts for the subspeciation of E. m. consobrinus, E. m. ”

“ Paler and grayer throughout; tawny areas restricted; gray areas clearer and less suffused; dark facial markings narrower and less [Pg 575] distinct; ventral surface of tail distinctly paler; feet lighter, clearer gray; nasals extend farther posteriorly with respect to premaxillae (Burt loc. cit.) .
From E. u. adsitus, the subspecies to the northeast, E. u. nevadensis differs in: Narrower dorsal stripes and facial markings; paler coloration of head, rump, sides, feet, and ventral surface of tail (Burt op. cit.: 299-300) . ”

“ Johnson (op. cit.:63) writes, "Each species [of Eutamias] has a characteristic habitat which differs from those of other species. Where two or more species occur together in a general locality they are usually mutually exclusive in their choice of foraging and nesting sites and in the time of breeding." Thus he classified the species of Californian chipmunks not only by morphologic characteristics but by habits and habitats as well. The characteristics of the skulls and skins of chipmunks probably reflect the habitats [Pg 631] in which these animals live. ”

“ Crown Pale Smoke Gray mixed with Cinnamon; upper facial stripe Fuscous; other facial stripes Sayal Brown mixed with Fuscous or Fuscous Black; anterior margin of ear Ochraceous-Tawny; posterior margin of ear and postauricular patch grayish white; median dorsal dark stripe Fuscous or black; other dorsal dark stripes black and mixed with gray, sometimes barely discernible; dorsal pair light stripes Smoke Gray; lateral pair of light stripes creamy white; rump and thighs Pale Smoke Gray mixed with Cinnamon; dorsal surface of tail Fuscous Black mixed with Tilleul Buff ”

“ Secondary sexual variation in chipmunks is small; the females are slightly larger than the males. This difference in size is so slight that it can be ignored when making taxonomic comparisons, for, large samples of males and females of like age and from the same locality were compared and were found statistically not to be significantly different. This is in agreement with Johnson (1943:70) and Hall (1946:329) .
Variations of taxonomic worth are treated in the accounts of species and subspecies. ”

“ When the word "significantly" is used in comparisons, it is meant to show that there is a significant statistical difference between two or more samples. Whenever eight or more specimens from one locality were available, the mean, range, standard deviation, standard error of the mean, and coefficient of variability were calculated. ”

“ Only adult specimens were used in comparison. "Aging" of specimens is discussed on page 587 of this paper.
The geographic range of each species and subspecies is not described in writing, for, the localities are plotted on maps along with the geographic range of each subspecies, and under "specimens examined" the locality of each specimen or series of specimens is listed. ”