In spite of a scarce fossil record and poor diversity, xenungulates cover a wide spatial range throughout South America: a new representative of Carodnia Simpson, 1935, attests to the northernmost occurrence of a carodniid xenungulate, ~4,500km away from previous occurrences (Saõ José de Itaboraí, Rio de Janeiro, Brazil; Chubut Province, Patagonia, Argentina) and very close to the Pacific Coast. A phylogenetic analysis of Xenungulata at the species level shows that Xenungulata and Carodniidae are monophyletic, while Etayoidae are potentially paraphyletic, at least with the selected taxonomic sample. Phylogenetic relationships among Xenungulata are [Notoetayoa gargantuai, Etayoa bacatensis [Carodnia sp. nov. [Carodnia feruglioi, C. cf. feruglioi, C. vieirai]]]. The new species is well differentiated from other xenungulates in having the m3 slightly smaller than m2 in terms of occlusal area and the entoconid and hypoconid almost at the same level on m3. It further differs from all other xenungulates but Etayoa bacatensis in possessing a transverse protolophid on m3. It is distinct from all other representatives of Carodnia in showing a precingulid strongly developed on m2-m3. Referral of the locality to the well-constrained early Eocene Mogollón Formation also confirms (i) the persistence of both carodniid and etayoid xenungulates well after the Paleocene-Eocene transition in South America and (ii) the absence of paleogeographic barrier for such large terrestrial mammals at the scale of South American landmass.
- Chacra-Salina group
- Itaboraian-Riochican South American Land Mammal ages
- Mogollón formation
- Phylogenetic analysis
- South American ungulates