Xenungulates are characterized bybilophodont M1–2 and M1–2, similar topyrotheres, and complex lophate third molars, similar touintatheres. Though other relationships, toarctocyonids 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-likeunguals, quite unlike any other meridiungulates. The discovery ofEtayoa in Colombia[6] made it clear that xenungulates are distinct from other groups:Etayoa lacks lophate molar talonid (in contrast toCarodnia) 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 primitiveastrapotheres.[7]
^Gelfo, Javier N.; García-López, Daniel A.; Bergqvist, Lilian P. (2020). "Phylogenetic relationships and palaeobiology of a new xenungulate (Mammalia: Eutheria) from the Palaeogene of Argentina".Journal of Systematic Palaeontology.18 (12):993–1007.doi:10.1080/14772019.2020.1715496.S2CID213052956.
Cifelli, Richard (1983). "Eutherian tarsals from the late Paleocene of Brazil".American Museum Novitates (2761).hdl:2246/5252.OCLC10601277.Cifelli 1983
Paula Couto, Carlos, de (1952). "Fossil mammals from the beginning of the Cenozoic in Brazil. Condylarthra, Litopterna, Xenungulata, and Astrapotheria".Bulletin of the American Museum of Natural History.99:355–394.hdl:2246/417.OCLC18189741.{{cite journal}}: CS1 maint: multiple names: authors list (link)Paula Couto 1952
Simpson, George Gaylord (1935). "Descriptions of the oldest known South American mammals, from the Río Chico Formation".American Museum Novitates. Publications of the Scarritt Expeditions, no. 24 (793).hdl:2246/2125.OCLC44083494.Simpson 1935
Villarroel, Carlos (1987). "Características y afinidades deEtayoa n. gen., tipo de una nueva familia de Xenungulata (Mammalia) del Paleoceno medio (¿) de Colombia".Comunicaciones Paleontologicas del Museo de Historia Natural del Montevideo.1 (19):241–253.OCLC18731966.Villarroel 1987
Bogotá Formation
Peñas Coloradas Formation
Mogollón Formation
Itaboraí Formation
