Arsinoitherium zitteli (Beadnell 1902, Figs. 1, 2; late Eocene, early Oligocene, 36-30 mya) was a sister to Gobiatherium and derived from a sister toPhenacodus. Wikipedia describes as, "an extinct genus of paenungulate mammal belonging to the extinct order Embrithopoda. It is related to elephants, sirenians, hyraxes and the extinct desmostylians." None of these candidates have any hint of the huge nasal and tiny frontal horns that make Arsinoitherium distinct. Another trait that makes Arsinoitherium distinct is its nearly complete arcade of teeth, none of them tusks, in which the canine is absent (or at least indistinct) and the medial incisor is missing. The premaxilla also redevelops an ascending process of the premaxilla, a trait not seen in mammals since their origin in the Triassic. |