Class [Mammalia] Linnaeus, 1758 - mammals Order Artiodactyla Owen, 1848 - even-toed ungulates see Order Cetartiodactyla Montgelard, Catzeflis & Douzery, 1997 Family Hippopotamidae Gray, 1821 - hippopotamuses 1 Genus Hippopotamus Linnaeus, 1758 - hippopotamus 2 Genus Choeropsis Leidy, 1853 - pygmy hippopotamus