Part 10

Study of the bacula of the Californian chipmunks supports Johnson's (op. cit.) conclusion that there are ten species, but suggests that there are three (not five) groups of species in California--as well as elsewhere within the geographic range of the subgenus Neotamias. The three groups are (see figs. 1-19): 1. minimus-group (E. alpinus, E. minimus, E. townsendii, E. sonomae, E. amoenus, E. dorsalis, and E. merriami); 2. quadrivittatus-group (E. quadrivittatus, E. ruficaudus, E. cinereicollis, and E. quadrimaculatus); and 3. speciosus-group (E. speciosus, E. panamintinus, E. umbrinus, E. palmeri, and E. bulleri).

Eutamias panamintinus, according to Howell (op. cit.:78) and Johnson (op. cit.:83), is a near relative of E. amoenus. But, the baculum in E. panamintinus more closely resembles that in E. speciosus than that in E. amoenus (compare figs. 5, 15, and 16). Consequently I have placed E. panamintinus in the speciosus-group.

In north-central Colorado, specimens that really are E. umbrinus (subspecies montanus) have, in the past (Howell op. cit.:82), been referred to E. quadrivittatus quadrivittatus, but the bacula of the two species differ markedly from each other (compare figs. 8-9 with 17-18) and permit the specimens readily to be correctly identified to species. Further, Howell (op. cit.:95) placed E. umbrinus (subspecies umbrinus and fremonti of current usage) in the quadrivittatus-group, whereas the structure of the baculum leads me to place E. umbrinus in the speciosus-group.

Thus, groups of species established on the basis of only skulls and skins, in a few instances differ from those established on a broader basis which includes the bacula.

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 in which these animals live. The characteristics of the bacula, on the other hand, may also reflect the habitats in which the animals live, but to a lesser degree. Because the structures of the bacula are probably less affected by the action of the external environment they probably indicate relationships between groups of species of chipmunks more clearly than do characteristics of the skulls and skins.

If the structures of the bacula indicate relationships between groups of species of chipmunks more clearly than do the characteristics of the skulls and skins, the close resemblance of the skulls of E. quadrivittatus and E. umbrinus may be thought of as convergence. The same can be said of E. amoenus and E. panamintinus.

LITERATURE CITED

FRILEY, C. E., JR.

1947. Preparation and preservation of the baculum of mammals. Jour. Mamm., 28:395-397, 1 fig., December 1.

HOWELL, A. H.

1929. Revision of the American chipmunks (genera Tamias and Eutamias). N. Amer. Fauna, 52:1-157, 10 pls., 9 maps.

JOHNSON, D. H.

1943. Systematic review of the chipmunks (genus Eutamias of California). Univ. California Publ. Zool., 48:63-148, 6 pls., 12 figs, in text, December 24.

WHITE, J. A.

1951. A practical method for mounting the bacula of small mammals. Jour. Mamm., 32:125, February 15.

Transmitted June 26, 1953.

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