Middle Miocene (Barstovian)
Tonopah, NV, USA
Very rare 38mm jaw section with two teeth of this early canid on 90mm matrix
Mammal, Canidae.

Tomarctus was a medium-sized member of the dog family known from the Middle Miocene of western North America.  It belongs to a subfamily of dogs, the Borophaginae, which is an Oligocene-Pliocene lineage that branched away from the one that includes modern dogs (foxes, coyotes, wolves).  This subfamily was quite diverse with small fox-like forms and large, hyena-like predators with teeth capable of cracking large bones (“borophagine” means “bone eater”).  Tomarctus occupies a stage in the history of borophagines just before the bone-cracking ability was accomplished.