Mammalia Linnaeus, 1758 - mammals Cetartiodactyla Montgelard, Catzeflis & Douzery 1997 see Order Cetartiodactyla Montgelard, Catzeflis & Douzery, 1997 Cetancodonta Arnason, Gullberg, Gretarsdottir, Ursing & Janke 2000 Hippopotamoidea Gentry & Hooker 1988 [Boisserie 2007]