With a length of 2.4 m (7 ft 10 in) and an estimated weight of 381 kg (840 lb) in S. mitis,[citation needed] it was a tapir-sized herbivore on the plains of early Oligocene South Dakota 33 million years ago.

It coexisted with other perissodactyls such as horses, brontotheres, and chalicotheres.

[6] Subhyracodon had no horns, relying more on its speed to escape from predators, but a species found at Wind Cave National Park had a pair of bony nasal ridges.

[citation needed] The genus Caenopus and species originally referred to as Aceratherium were synonymized into Subhyracodon.

[7] It has been suggested to be one of the oldest known members of the subfamily Elasmotheriinae by some studies,[8] though other studies place it firmly outside the Rhinocerotinae-Elasmotheriinae split.