Phylum [Vertebrata] Lamarck, 1801 see Infraphylum Vertebrata Lamarck, 1801
   Class Mammalia Linnaeus, 1758 - mammals
     Subclass Theria Parker & Haswell, 1897
       Infraclass Eutheria Gill, 1872
         Cohort Epitheria McKenna, 1975
           Superorder Ungulata Linnaeus, 1766
             Order Perissodactyla Owen, 1848 - odd-toed ungulates
               Suborder Hippomorpha Wood, 1937
                 Family Equidae Gray, 1821 - horses, zebras, and asses
                   1 Genus †Anchitherium von Meyer, 1844
                   2 Genus †Hipparion de Christol, 1832
                   3 Genus ‡Hippidion Owen, 1869
                   4 Genus †Hyracotherium Owen, 1840
                   5 Genus †Merychippus Leidy, 1857
                   6 Genus †Mesohippus Marsh, 1875
                   7 Genus †Parahippus Leidy, 1858