A new phylogeny of the Superfamily Rhinocerotoidea is proposed, based upon an analysis of shared derivrd characters of the skull, teeth and skeleton. Hyrachyus is considered the primitive sister-taxon of the three rhinocerotoid families (Amynodontidae, Hyracodontidae, Rhinocerotidae) , and the amynodonts appear to be the sister-group of hyracodonts and rhinocerotids. The relationships of primitive hyracodonts and rhinocerotids are clarified. Menoceras and Pleuroceras (new Subfamily Menoceratinae) are removed from the Diceratheriinae, since they appear to be more closely related to higher rhinoceroses than they are to Dicel-atherium. Of the three major monophyletic groups of higher rhinocerotids (aceratherines, teleoceratines and rhinocerotines), the last two groups are more closely related to each other than either is to areratherines. Toxothertum and Schirotherozdes are tentatively removed from the Rhinocerotoidea and placed in the Lophiodontidae.
A new genus and species of amynodontid rhinoceros, Rostriamynodon grangeri, from the early Late Eocene of Inner Mongolia, People's Republic of China, is the most primitive amynodontid recognized to date. Rostriamynodon exhibits the major diagnostic characteristics of amynodontids: quadratic M3, preorbital fossa, and loss of upper and lower P1. It differs from more advanced members of the family in its long preorbital region and lower cheek tooth morphology. Comparisons with other Eocene ceratomorphs show the crucial position Rostriamynodon has in determining phylogenetic relationships between rhinocerotoids and tapiroids. Evidence is presented for the monophyly of the Rhinocerotoidea, including amynodontids.
Four species of rhinoceros occur together in the Barstovian (middle Miocene) faunas of southeast Texas, a unique situation in the Miocene of North America. Two are assigned to normal contemporary High Plains species of Aphelops and Teleoceras, and two to dwarf species of Peraceras and Teleoceras. The dwarf Peraceras is a new species, P. hessei. The dwarf Teleoceras is assigned to Leidy's (1865) species “Rhinoceros” meridianus, previously referred to Aphelops. “Aphelops” profectus is here reassigned to Peraceras.The late Arikareean (early Miocene) Derrick Farm rhino, erroneously referred to “Caenopus premitis” by Wood and Wood (1937), is here referred to Menoceras arikarense. Menoceras barbouri is reported from the early Hemingfordian (early Miocene) Garvin Gully local fauna of southeast Texas. The rhinos from the early Clarendonian Lapara Creek Fauna are tentatively referred to Teleoceras cf. major.The three common genera of middle late Miocene rhinoceroses of North America (Aphelops, Peraceras, Teleoceras) are rediagnosed. Aphelops and Peraceras are more closely related to the Eurasian Aceratherium and Chilotherium (all four together forming the Aceratheriinae) than they are to the American Teleoceras. Contrary to Heissig (1973), Teleoceras is more closely related to the living rhinoceroses and their kin (together forming the Rhinocerotini) than it is to the Aceratheriinae.
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