Class Mammalia Linnaeus, 1758 - mammals
   Order Artiodactyla Owen, 1848 - even-toed ungulates see Order Cetartiodactyla Montgelard, Catzeflis & Douzery, 1997
     Family Hippopotamidae Gray, 1821 - hippopotamuses
       Genus Hexaprotodon Falconer & Cautley, 1836
         1 †[Hexaprotodon sivalensis] (Falconer & Cautley, 1836)
         2 Hexaprotodon liberiensis (Morton, 1849) - pygmy hippopotamus see Choeropsis liberiensis (Morton, 1844)
         3 ‡Hexaprotodon madagascariensis (Guldberg, 1883) see Hippopotamus madagascariensis Guldberg, 1883