Subhyracodon is an extinct genus of cow-sized rhinoceroses. With a length of 2.4 m (8 ft) and a weight estimated of 381.3 kg (in S. mitis), it was a tapir-sized herbivore on the plains of early Oligocene South Dakota 33 million years ago (White River Fauna), smaller than only the Brontops and the chalicotheres. Subhyracodon had no horns, relying more on its speed to escape, but a species found at Wind Cave National Park had a pair of bony nasal ridges. The genera Caenopus and Aceratherium were both synonymized with Subhyracodon