Protomarctus is an extinct monospecific genus of the Borophaginae subfamily of canids native to North America. They lived during the Middle Miocene 16.0—13.6 Mya, existing for approximately .[1] It was an intermediate-size canid, and more predaceous than earlier borophagines.[2]
The first specimen was found in Thomson Quarry, Sheep Creek Formation, Nebraska in a Hemingfordian layer. Specimens have since been found in present-day Colorado, as far west as California and as far southwest as New Mexico.[1] They were short-faced, heavy-jawed canines.