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 Artiodactyla Owen, 1848 - even-toed ungulates see Order Cetartiodactyla Montgelard, Catzeflis & Douzery, 1997
               Suborder Tylopoda "Illiger, 1811"
                 Family †Protoceratidae Marsh, 1891
                   1 Genus †Protoceras Marsh, 1891
                   2 Genus †Syndyoceras Barbour, 1905
                   3 Genus †Synthetoceras Stirton, 1932