Hayoceros was named by Skinner (1942) and named as a subgenus of Tetrameryx by Frick 1937; raised to genus level. It was assigned to Antilocapridae by Skinner (1942) and Carroll (1988).
It was about 1.8 metres (5.9 ft) in body length, and, in most respects, resembled modern pronghorns. However, in addition to the pair of forked horns located above the eyes, as in modern pronghorns, it also possessed a second, longer and unforked, pair on the back of the skull. Most likely, males used these to fight in a fashion similar to modern pronghorns, locking horns and then pushing until the opponent gave in.