Tomarctus is a canid genus of the extinct subfamily Borophaginae which inhabited most of North America during the late Early Miocene to the Early Barstovian age of the Middle Miocene (23—16 mya). Tomarctus existed for approximately 6.83 million years. This animal shared a period of time and ecology with a variety of other bear dogs like the giant mustelid genus of bone-crushing canidae, Cynarctoides. As the bear dogs and giant mustelids became extinct, Tomarctus further radiated to fill a line of dogs which filled the hyena-like fruit eating and bone-crushing niches.