Squirrel In Action

Taxonomy
The living squirrels are divided into five subfamilies, with about 50 genera and nearly 280 species. The oldest squirrel fossil, Hesperopetes, dates back to the Chadronian (Late Eocene, about 40–35 million years ago), and is similar to modern flying squirrels.
During the latest Eocene to the Miocene, there were a variety of squirrels which cannot be assigned with certainty to any living lineage. At least some of these probably were variants of the oldest, basal "proto-squirrels" (in the sense that they lacked the full range of living squirrels' autapomorphies). The distribution and diversity of such ancient and ancestral forms suggests that the squirrels as a group might have originated in North America.