Arikareean

thumb|Daeodon shoshonensis life restoration thumb|Daeodon (Dinohyus) hollandi, complete skeleton from the Agate Fossil Beds National Monument|Agate Springs Fossil Quarry in Nebraska. See text for nomenclature history

The genus Leptocyon (Greek: leptos slender + cyon dog) includes 11 species and is the oldest known canine. They were small and weighed around . They first appeared in North America around 34 million years ago in the Oligocene, at the same time as the Borophaginae, with whom they share features, indicating that these were two sister groups. Borophaginae skull and dentition were designed for a powerful killing bite compared with the Leptocyon which were designed for snatching small, fast-moving prey. The species L. delicatus is the smallest canid to have existed. At the close of their genus 9 mi

Protolabis is an extinct genus of camelid endemic to North America. It lived from the Early to Late Miocene 20.4—5.3 mya, existing for approximately . Fossil distribution is widespread from Nicaragua, Central America to Montana and throughout the western U.S.

Merychyus is an extinct genus of oreodont of the family Merycoidodontidae, endemic to North America. It lived during the Miocene, 20.4—10.3 mya, existing for approximately . Fossils are widespread through the central and western United States.