COMPARISON BETWEEN LIVING ASIAN AND NORTH AMERICAN PIKAS
Ochotona princeps and O. collaris of North America and O. alpina and O.hyperborea of Asia were once considered to be a single species based on skull morphology and external features (Argyropulo 1948;
Corbet 1978). These same species are considered distinct, based on chromosomal data. Because they share the number of chromosomes (2n = 68), a closer phylogenetic relationship was hypothesized for Ochotona pusilla and the North American species (Ochotona princeps and O. collaris) (Vorontsov and Ivanitskaya 1973). This hypothesis is supported by the fossil record and by the presence of plesiomorphic features shared in Ochotona pusilla in some P3 of both North American species. It may be suggested that Ochotona pusilla, O. collaris and O. princeps likely had the same ancestral form, the divergence of which took place at least by the earliest Pleistocene. The oldest ancestral taxon probably was similar to the pikas from Cumberland and Trout Caves as well as from Porcupine Cave, having small size and a wide confluence between anteroconid and posteroconid. It is reasonable to suggest that the development of the living forms, at least of Ochotona princeps, probably occurred during the end of Middle or beginning of Late Pleistocene. As noted above, ochotonid remains from the upper levels of the Velvet Room are similar to Ochotona princeps.
Comparisons between recent Ochotona pusilla, O. collaris, and O. princeps show that they differ significantly in their size, pelage, biology, skull morphology, tooth structure, ear bones, baculum morphology, and behavioral data. They differ as well by diversity of their habitats and elevations. Ochotona pusilla is a burrowing steppe-dwelling animal; in arid and desert steppes it is generally found in wet biotopes with thick grass and bushes mainly in Northern Kazakhstan (Ognev 1940;
Gureev 1964). Today Ochotona princeps is talus-dwelling species distributed in mountainous area of West North America (Smith 1974,
1981). Ochotona collaris is also a typical rock and talus-dwelling pika, distributed in the mountains of central and southern Alaska and northwestern Canada (Broadbooks 1965).