What is "subhyracodon"

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