Dentition of Gobiohyus and a Reevaluation of the Helohyidae (Artiodactyla)

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Abstract
The late Eocene bunodont artiodactyl Gobiohyus is reevaluated on the basis of new dental material and contains three species—G. orientalis, G. pressidens, and G. robustus. Gobiohyus yuanchuensis Young (1937) is reassigned as ?Indohyus yuanchuensis. Gobiohyus is referred to the Helohyidae, which also includes Helohyus (and Lophiohyus as a junior synonym of Helohyus),Indohyus, Raoella, Kunmunella, and Bunodentus. Helohyidae are removed from the Dichobunoidea and placed in the Anthracotherioidea because they share with anthracotheriids a downturned mandibular angle, squared upper molars, hypocone strongly reduced or lost, hypertrophied metaconule on the posterolingual angle of upper molars, lower molars increasing in size from M1 through M3, and enlarged M3 hypoconulid. Helohyids are derived anthracotherioids in their bunodonty or incipient bunodonty and in their small paraconules which are close to the protocone. Anthracotheriids are derived relative to helohyids in other dental features. Dichobunoids, achaenodonts, choeropotamids, entelodonts, and cebochoerids have at one time or another been allied to Gobiohyus or other helohyids; dichobunoids, entelodonts, and cebochoerids are not close to helohyids, but the evidence for achaenodonts and choeropotamids is equivocal.