A revision of the genus Orohippus (Perrisodactyla, Equidae). American Museum novitates ; no. 1864

Abstract

"The genus Orohippus, known only from the Bridger formation of southwestern Wyoming, closely resembles Hyracotherium, its probable Wasatchian ancestor. The dentition of Orohippus differs from that of Hyracotherium largely in the progressive molarization of the premolars in the former genus. A rather minor, but functionally significant, structural character of the ankle joint of the equids, which appears for the first time in Orohippus, is discussed. Of the 12 named species that have been referred to the genus, five (O. major, O. pumilus, O. progressus, O. sylvaticus, and O. agilis) are recognized. The specific evolution within the genus and the relationships to species of Hyracotherium are discussed"--P. 38.