Full reference: O. P. Hay. 1902. Bibliography and Catalogue of the Fossil Vertebrata of North America. Bulletin of the United States Geological Survey 179:1-868
Parent taxon: Perissodactyla according to J. A. Remy 2012
See also Astibia et al. 2000, Badiola et al. 2002, Bernor 1985, Carroll 1988, Franzen 2006, Froehlich 2002, Hay 1902, Hooker 1986, Hooker 1994, Hooker and Dashzeveg 2004, Prothero and Schoch 1989 and Remy 2000
Sister taxa: Anthracobunidae, Brontotheriidae, Cambaytheriidae, Cambaytherium, Chelodactyla, Desmostylia, Equina, Ghazijhippus, Hallensia, Hippopotamus iravaticus, Hyracotheriidae, Lophodontomorpha, Mesaxonia, Mesolambdolophus, Nakusia, Paschatherium, Perissobune, Rhinocerotida, Selenida, Skopaiolophus, Solidungula, Stereopterna, Tapiromorpha, Teilhardimys, Titanotheriomorpha, Triplopidae
Subtaxa: Cymbalophus Equidae Pachynolophidae Palaeotheriidae
Ecology: ground dwelling browser-grazer