New insights on the anatomy, paleobiology, and biostratigraphy of Xenungulata (Mammalia) from the Paleogene of South America

Abstract

Xenungulata is a group of early Paleogene mammals endemic to South Americathat remains poorly understood. The first species described within this order, Carodniaferuglioi, has laid the basis for the homonymous zone, currently positioned betweenthe Peligran (Danian) and Itaboraian (Ypresian) South American Land Mammals Ages.Through the study of new specimens and a revaluation of materials from historical collections,we have identified remains belonging to Carodniidae and Etayoidae xenungulatesand assigned them to Carodnia feruglioi and Notoetayoa gargantuai. This has ledto a reinterpretation of their dental characteristics, setting the foundations for establishingdental homologies with other native ungulates of South America. Additionally, weintroduce Carodnia karuen sp. nov., discovered at the lower Paleocene levels in CerroRedondo locality in Patagonia, Argentina. The specimen extends the biostratigraphicand biochronological significance of Carodnia as a fossil guide in the Paleocene ofsouthern South America. A paleobiological analysis of these specimens focused oncomparing the variation in mandibular morphology and measurements within Carodniidae.This approach has allowed the identification of a potential sexual dimorphism patternat the generic level for Carodnia. The findings imply that Carodnia feruglioi fromthe early Paleocene of Patagonia and the early Eocene Carodnia vieirai from Itaboraí,Brazil, probably maintained a sexual variation in mandibular width and height.