A new genus of rhinocerotoid from the Eocene of Utah and the status of North American “Forstercooperia”

Abstract

A skeleton of a primitive rhinocerotoid from the Uintan (middle Eocene) of Utah provides the basis for a new genu s and species, Uintaceras radinskyi; Hyrachyus grande Peterson, 1919 is a nomen dubium. The anterior dentition of thi s specime n is unlike that of any other known rhinocerotoid, although it most resembles the anterior teeth of so me primitive rhinocerotids. The cheek teeth are primitive in morphology and similar to tho se of specimens referred to " Forstercooperia" grandis. North American specimens referred previously to Forstercooperia are here referred to this new genus. This taxonomic change implies that the evolution of indricotheriine hyracodontids was restricted to Eura sia. The postcranial skeleton of Uintaceras is robu st and shows many primitive characters. including a tetradactyl manu s. Uintaceras is the sister taxon of the Rhinocerotidae and demonstrates that rhinocerotids, at their origin, retained the primitive condition for many characters, includ ing some that have been used to unite rhinocerotids with other rhinocerotoids, such as indricotheriine hyracodontids.

Earliest known unequivocal rhinocerotoid sheds new light on the origin of Giant Rhinos and phylogeny of early rhinocerotoids

“…In spite that P. meiomenus is close to the Late Eocene eggysodontids Proeggysodon and Guangnanodon in size (based on length of lower molar series)1831, eggysodontids differ from the latter by having complete upper premolars, large and nearly vertically oriented canines, primitively speculate incisors that vary in number (2 or 3) across different genera, and more molarized premolars3233, and the known craniodental features of eggysodontids34 are more comparable to those of rhinocerotids rather than forstercooperiines. The enigmatic genus Uintaceras was considered as the sister group of rhinocerotids for its distinctive features of anterior dentition (buccolingually compressed upper incisors with a triangular profile) and characteristics of cheek teeth and postcranial elements835. Although Holbrook and Lucas35 pointed out some cranial differences between forstercooperiines and Uintaceras , it should be noted that the reconstruction of skull of Uintaceras was mainly based on laterally compressed and distorted materials of UCMP 69722 and UW 2410.…”

“…The enigmatic genus Uintaceras was considered as the sister group of rhinocerotids for its distinctive features of anterior dentition (buccolingually compressed upper incisors with a triangular profile) and characteristics of cheek teeth and postcranial elements835. Although Holbrook and Lucas35 pointed out some cranial differences between forstercooperiines and Uintaceras , it should be noted that the reconstruction of skull of Uintaceras was mainly based on laterally compressed and distorted materials of UCMP 69722 and UW 2410. Some characters used for distinguishing Uintaceras from fostercooperines show similarities in mentioned taxa, when compared to those of other early rhinocerotoids.…”

“…In terms of dentitions, they are similar in having non-molarized premolars, presence of M3 metastyle and short diastema. It is interesting to mention that some similarities between Uintaceras and amynodontids in both dental and postcranial characters were mentioned, but considered as a result of scaling35. The most conspicuous feature that distinguishes Uintaceras from fostercooperines lays in its buccolingually compressed upper incisors with triangular profile.…”

The Phylogeny and Classification of Tapiromorph Perissodactyls (Mammalia)

“…This charside of the hyracodontid clade and closer to the amyacter may not prove to be a good synapomorphy, since nodontid/rhinocerotid clade. Uintaceras, as suggested this foramen is absent in some chalicotherioids [e.g., by Holbrook and Lucas (1997), is united with Chalicotherium (Zapfe, 1979)]. Another character, the rhinocerotids.…”

New Material of Eocene Helaletidae (Perissodactyla, Tapiroidea) from the Irdin Manha Formation of the Erlian Basin, Inner Mongolia, China and Comments on Related Localities of the Huheboerhe Area

“…Among brontotheres, Metatelmatherium cristatum was considered as a junior synonym of the Uintan Metatelmatherium ultimum from North America (Mihlbachler, 2008). Among hyracodontids, the North American Triplopus had a temporal distribution ranging from the Uintan to Duchesnean, and Uintaceras, which is similar to Fostercooperia to some extent, is from the Uintan (Radinsky, 1967;Holbrook and Lucas, 1997;Prothero, 1998). On the other hand, Rostriamynodon was considered more primitive than the Uintan Amynodon from North America (Wall and Manning, 1986).…”