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 genus and species, Uintaceras radinskyi: Hyrachyus grande Peterson, 1919 is a nomen dubium. The anterior dentition of this specimen is unlike that of any other known rhinocerotoid, although it most resembles the anterior teeth of some primitive rhinocerotids. The cheek teeth are primitive in morphology and similar to those 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 Eurasia. The postcranial skeleton of Uintaceras is robust and shows many primitive characters, including a tetradactyl manus. Uintaceras is the sister taxon of the Rhinocerotidae and demonstrates that rhinocerotids, at their origin, retained the primitive condition for many characters, including some that have been used to unite rhinocerotids with other rhinocerotoids, such as indricotheriine hyracodontids.