''Archaeogaia'' is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

notoungulates Notoungulata is an extinct order of ungulates that inhabited South America from the early Paleocene to the end of the Pleistocene, living from approximately 61 million to 11,000 years ago. Notoungulates were morphologically diverse, with forms re ...

that lived during the Early and Middle

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

of what is now

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. It is one of the oldest known unequivocal notoungulates.

Description

This animal is only known from a fragmentary left mandible preserving three molars. ''Archaeogaia'' was characterized by a first molar slightly shorter than the second, both being larger than the third, all of them being low-crowned (brachydont); a talonid shorter than the trigonid, a metaconid distally positioned and taller than the protoconid, a reduced paraconid on the second molar, a straight metalophid on the second and third molar (running mesially to form an obtuse angle in the labial margin on the second molar, and more traversally on the third), a transversal entoloph, a mesial cingulid extending from the medial area to the lingual area on the molars, and a distal cingulid connected with the hypoconulid with the mesial surface of the entoconid on the second and third molars.

Classification

''Archaeogaia macachaae'' was first described in 2020, based on a single fossil from the

Mealla Formation The Mealla Formation is a geological formation of the Santa Bárbara Subgroup, part of the Salta Group in the Salta Basin in northwestern Argentina whose strata date back to the Middle to Late Paleocene of the Paleogene. Description The Me ...

, in the

Salta Province Salta () is a Provinces of Argentina, province of Argentina, located in the northwest of the country. Neighboring provinces are from the east clockwise Formosa Province, Formosa, Chaco Province, Chaco, Santiago del Estero Province, Santiago del Es ...

. Due to the presence of a transversal entolophid and to features of the protolophid, metalophid and hypolophid, ''Archaeogaia'' is considered a member of the Notoungulata. It is however unclear which phylogenetic position it occupied within the group, due to the extreme fragmentation and to the plesiomorphic characteristics of the holotype fossil. ''Archaeogaia'' is considered to be the oldest known notoungulate, perhaps along the better known

Henricosborniidae Henricosborniidae is a family of extinct notoungulate mammals known from the Late Paleocene to Middle Eocene of Argentina, Bolivia and Brazil. The name honors U.S. paleontologist Henry Fairfield Osborn. Description Henricosborniidae is a grou ...

'' Simpsonotus''.

References

{{Taxonbar, from=Q110448306 Notoungulates Paleocene mammals of South America Paleogene Argentina Fossils of Argentina Tiupampan Peligran Fossil taxa described in 2020 Prehistoric placental genera Salta Basin