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 America that remains poorly understood. The first species described within this order, Carodnia feruglioi, has laid the basis for the homonymous zone, currently positioned between the 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 xenungulates and assigned them to Carodnia feruglioi and Notoetayoa gargantuai. This has led to a reinterpretation of their dental characteristics, setting the foundations for establishing dental homologies with other native ungulates of South America. Additionally, we introduce Carodnia karuen sp. nov., discovered at the lower Paleocene levels in Cerro Redondo locality in Patagonia, Argentina. The specimen extends the biostratigraphic and biochronological significance of Carodnia as a fossil guide in the Paleocene of southern South America. A paleobiological analysis of these specimens focused on comparing the variation in mandibular morphology and measurements within Carodniidae. This approach has allowed the identification of a potential sexual dimorphism pattern at the generic level for Carodnia. The findings imply that Carodnia feruglioi from the early Paleocene of Patagonia and the early Eocene Carodnia vieirai from Itaboraí, Brazil, probably maintained a sexual variation in mandibular width and height.