Bear Surgery

Fossil bears
The earliest members of Ursidae belong to the extinct subfamily Amphicynodontinae, including Parictis (late Eocene to early middle Miocene, 38-18 million years (Ma) ago) and the slightly younger Allocyon (early Oligocene, 34-30 Ma), both from North America. These animals looked very different from today's bears, being small and raccoon-like in overall appearance, and a diet perhaps more similar to that of a badger. Parictis does not appear in Eurasia and Africa until the Miocene. It is unclear whether late Eocene ursids were also present in Eurasia, although faunal exchange across the Bering land bridge may have been possible during a major sea level low stand as early as the late Eocene (~37 Ma) and continuing into the early Oligocene. European genera morphologically very similar to Allocyon, and also the much younger American Kolponomos (~18 Ma), are known from the Oligocene, including Amphicticeps and Amphicynodon.
The raccoon-sized, dog-like Cephalogale is the oldest-known member of the subfamily Hemicyoninae which first appeared during the middle Oligocene in Eurasia ~30 Ma ago. The subfamily also includes the younger genera Phoberocyon (~20-15 Ma), and Plithocyon (~15-7 Ma).
A Cephalogale-like species gave rise to the genus Ursavus during the early Oligocene (30-28 Ma); this genus proliferated into many species in Asia and is ancestral to all living bears. Species of Ursavus subsequently entered North America together with Amphicynodon and Cephalogale during the early Miocene (21-18 Ma).