Systematic revision of Antepithecus brachystephanus Ameghino, 1901, and dental eruption sequence in Eocene “notopithecines” (Notoungulata) from Patagonia

Abstract

In this contribution, a detailed systematic study of all species previously placed into the genus Antepithecus, a Barrancan (middle Eocene) “notopithecine” from Patagonia, is performed. In addition, other species described by Ameghino were studied and are also included in this taxon. The comparative morphological description allows corroborating and introducing new synonyms, and recognizing one valid species, Antepithecus brachystephanus. Its diagnosis is expanded and the number of specimens referred to this species is significantly increased. Morphological ontogenetic variations in dentition are recognized and compared with other “notopithecines”. A particular eruption sequence of permanent premolars is ascertained for the Patagonian taxa Notopithecus, Antepithecus, and Transpithecus. These three Casamayoran “notopithecines” have their upper and lower milk molars replaced by permanent premolars in a posterior-anterior direction, P/p4, P/p3, P/p2, contrasting with other notoungulates, including the Mustersan “notopithecine” Guilielmoscottia. This peculiar eruption sequence in Casamayoran “notopithecines” and its heterogeneity within the group could reflect a relevant phylogenetic character to clarify inter-specific relationships.