Extinct order of mammals
Xenungulata ("strange ungulates") is an order of extinct and primitive South American hoofed mammals that lived from the Late Paleocene to Early Eocene (Itaboraian to Casamayoran in the SALMA classification). Fossils of the order are known from deposits in Brazil, Argentina, Peru,[4] and Colombia. The best known member of this enigmatic order is the genus Carodnia, a tapir-like and -sized animal with a gait similar to living African elephants.[5]
Description
Xenungulates are characterized by bilophodont M1–2 and M1–2, similar to pyrotheres, and complex lophate third molars, similar to uintatheres. Though other relationships, to arctocyonids for example, have been suggested, no proofs thereof have been found. The foot bones of xenungulates were short and robust and their digits terminated in broad, flat, and unfissured hoof-like unguals, quite unlike any other meridiungulates. The discovery of Etayoa in Colombia[6] made it clear that xenungulates are distinct from other groups: Etayoa lacks lophate molar talonid (in contrast to Carodnia) and, since no distinct lophodonty is present in basal pyrotheres, there is reason to assume that bilophodonty evolved separately in xenungulates and pyrotheres. Xenungulates also show some dental similarity to primitive astrapotheres.[7]
Taxonomy
Cifelli 1983 grouped Carodnia with pyrotheres based on a similarity in astragalus morphology, but later concluded that this observation was incorrect.[8]
Notoetayoa is most closely related to Etayoa.[9]
Distribution
Xenungulata fossils have been found in:[10]
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