Mammalia - Perissodactyla - Hyracodontidae

Synonym: Hyracodon apertus Sinclair 1922

Belongs to Hyracodon according to D. R. Prothero 1996

Sister taxa: Hyracodon browni, Hyracodon medius, Hyracodon nebraskensis, Hyracodon petersoni, Hyracodon priscidens

Type specimens:

• Hyracodon leidyanus: Its type locality is Crow Buttes (Whitney-South Dakota), which is in a Whitneyan terrestrial horizon in South Dakota
• Hyracodon apertus:

Ecology: ground dwelling browser

Average measurements (in mm): P4 22.1 x 27.8, M1 22.1 x 26.3, M2 19.2 x 27.7, p4 23.2 x 16.9, m1 22.8 x 14.9, m2 24.3 x 15.5