Mammalia - Artiodactyla - Merycoidodontidae

Alternative combinations: Mesoreodon longiceps, Pseudodesmatochoerus longiceps

Synonym: Phenacocoelus stouti Schultz and Falkenbach 1950

Belongs to Merycoides according to A. R. Tabrum and R. Nichols 2001

Sister taxa: Merycoides harrisonensis, Merycoides pariogonus, Merycoides relictus

Type specimens:

• Merycoides longiceps: Its type locality is North Boulder Valley, which is in a Harrisonian terrestrial horizon in the Renova Formation of Montana
• Phenacocoelus stouti: Its type locality is Guernsey, which is in a Harrisonian terrestrial horizon in the Upper Harrison Beds Formation of Wyoming.