Xenungulata ("strange ungulates") is an order of extinct and primitive South American hoofed mammals that lived from the

Late Paleocene The Thanetian is, in the ICS Geologic timescale, the latest age or uppermost stratigraphic stage of the Paleocene Epoch or Series. It spans the time between . The Thanetian is preceded by the Selandian Age and followed by the Ypresian Age (p ...

to Early Eocene (

Itaboraian The Itaboraian ( pt, Itaboraiense) age is a period within the Early Eocene geologic time (53.0–50.0 Ma) epoch of the Paleogene, used more specifically with South American land mammal ages (SALMA). It follows the Riochican and precedes the Cas ...

Casamayoran The Casamayoran ( es, Casamayorense) age is a period of geologic time (50.0–48.0 Ma) within the Early Eocene epoch of the Paleogene, used more specifically within the South American land mammal age (SALMA) classification. It follows the Itaboraia ...

in the SALMA classification). Fossils of the order are known from deposits in

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = National seal , national_motto = "Firm and Happy f ...

, and Colombia. The best known member of this enigmatic order is the genus '' Carodnia'', a

tapir Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a pig, with a short, prehensile nose trunk. Tapirs inhabit jungle and forest regions of South and Central America, with one species inh ...

-like and -sized animal with a gait similar to living African elephants.

Description

Xenungulates are characterized by

bilophodont The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, ...

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

ungual An ungual (from Latin ''unguis'', i.e. ''nail'') is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and ungulates have ungual phalanges, as did the sauropod Sauropoda (), whose members are known as sauropods (; ...

s, quite unlike any other meridiungulates. The discovery of ''

Etayoa ''Etayoa'' is an ungulate of the family Carodniidae in the order Xenungulata that lived during the Early Eocene (~ 55 Ma) in northern South America. Etymology The genus of the type species ''Etayoa bacatensis'' was named by palaeontologist C ...

'' in Colombia 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 Astrapotheria is an extinct order of South American and Antarctic hoofed mammals that existed from the late Paleocene to the Middle Miocene, ."The uruguaytheriine Astrapotheriidae from the rich middle Miocene Honda Group of the upper Magdalen ...

Taxonomy

grouped ''Carodnia'' with pyrotheres based on a similarity in

astragalus ''Astragalus'' is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to tempe ...

morphology, but later concluded that this observation was incorrect. '' Notoetayoa'' is most closely related to ''Etayoa''.

Distribution

Xenungulata fossils have been found in:Xenungulata
at Fossilworks.org *

Bogotá Formation The Bogotá Formation ( es, Formación Bogotá, E1-2b, Tpb, Pgb) is a geological formation of the Eastern Hills and Bogotá savanna on the Altiplano Cundiboyacense, Eastern Ranges of the Colombian Andes. The predominantly shale and siltstone form ...

, Colombia * Peñas Coloradas Formation,

Riochican The Riochican ( es, Riochiquense) age is a period of geologic time (57.0–54.0 Ma) within the Paleocene and Eocene epochs of the Paleogene, used more specifically within the South American land mammal ages (SALMA). It follows the Peligran and prec ...

, Argentina * Mogollón Formation,

, Peru *

Itaboraí Formation The Itaboraí Formation ( pt, Formação Itaboraí) is a highly fossiliferous geologic formation and LagerstätteKellner & Campos, 1999, p.399 of the Itaboraí Basin in Rio de Janeiro, southeastern Brazil. The formation reaching a thickness of i ...

, Brazil

References

Bibliography

* * * * * * * * * {{Taxonbar, from=Q142395 Meridiungulata Paleocene mammals of South America Eocene mammals of South America Paleocene first appearances Eocene extinctions Casamayoran Itaboraian Riochican Fossil taxa described in 1952