Xenungulata

Xenungulates are characterized by bilophodont M^1–2 and M_1–2, 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 lophondonty 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]

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]

Locations of Xenungulata fossils
Bogotá Formation
Peñas Coloradas Formation
Mogollón Formation
Itaboraí Formation

Xenungulata fossils have been found in:[10]

• Bogotá Formation, Casamayoran, Colombia
• Peñas Coloradas Formation, Riochican, Argentina
• Mogollón Formation, Itaboraian-Riochican, Peru
• Itaboraí Formation, Itaboraian, Brazil