Late Oligocene

Chandler Bridge Formation

Summerville, SC, USA

16mm tooth

Mammal, Whale.

The squalodont whales of the Oligocene and Miocene were fully-aquatic yet primitive because they still had heterodont teeth reminiscent of their land-based Eocene ancestors.  Their teeth still had the general form of incisors/canines and premolars/molars but were following a trend toward homodonty as seen in modern toothed whales (odontocetes).  They died out by the end of the Miocene.