Xenungulata

Xenungulata Temporal range: Paleocene to Eocene
Carodnia vieirai
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Subclass:	Theria
Infraclass:	Eutheria
Superorder:	†Meridiungulata
Order:	†Xenungulata Paula Couto 1952
Family and genera[1]
†Carodniidae Paula Couto 1952[2] †Carodnia Simpson 1935 †Etayoa Villarroel 1987 †Notoetayoa Gelfo, López & Bond 2008

Xenungulata ("strange ungulates") is an order of extinct and primitive South American hoofed mammals known from deposits in Brazil, Argentina, 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.^[3]

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^[4] 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.^[5]

Cifelli 1983 grouped Carodnia with pyrotheres based on a similarity in astragalus morphology, but later concluded that this observation was incorrect.^[6]

Notoetayoa is most closely related to Etayoa.^[7]

References