CONCLUSIONS

Ochotonids originated in Central Asia during the Oligocene, flourished during Miocene and Pliocene and decrease their diversity during Pleistocene.

The first dispersal of the genus Ochotona into the Europe occurred at the beginning of Pliocene.

There have been repeated migration events to the North America.

The first ochotonid' invasion into the Western Hemisphere occurred at the beginning of Miocene when Oreolagus appeared.

The next immigration occurred during the late Miocene (Hemphillian), recorded with the first appearance of the genus Ochotona.

The ancestral forms of the living pikas migrated to North America at the beginning of Early Pleistocene and they distributed as far south and east west as the Appalachians and Colorado.

The earliest Irvingtonian pikas are closer to pikas of "O. pusilla" group, having some plesiomorphic characters.

Recent North American pikas differ significantly from Ochotona pusilla by their external features and their habitat.