Borophagus littoralis

This is a jaw from a dog with specialized teeth for crushing bones. Notice how the two large teeth (premolar 4 and molar 1) are crowded together to make a virtual single crushing platform. In this adaptation, the p4 is enlarged to match the size of the m1, while the other premolars and molars are of unremarkable size.

This species (recently revised) represents a cluster of widespread, successful species that flourished in the Miocene, though no representative survived into the Pleistocene.