''Notonychops'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of mammal, belonging to the order

Litopterna Litopterna (from grc, λῑτή πτέρνα "smooth heel") is an extinct order of fossil hoofed mammals from the Cenozoic era. The order is one of the five great orders of South American ungulates that were endemic to the continent, until the G ...

, that lived during the Middle to Late

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

in what is today

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the souther ...

Description

This genus is only known from a fragmentary

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bon ...

and

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The ...

, and it is therefore difficult to hypothesize on its general appearance. ''Notonychops'' had a specialized set of teeth, with selenodont lower molars and

premolar The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth ...

s with a strong parastyle and a metastyle with paracone and protocone, and the first premolar was absent. The molars had a strong parastyle, and were similar to those of primitive tillodonts, such as '' Esthonyx'', and of little known litopterns such as '' Indalecia''.

Classification

''Notonychops powelli'' was first described by Miguel Soria in 1989, based on fossilized remains found in the lower member of the

Rio Loro Formation Rio or Río is the Portuguese, Spanish, Italian, and Maltese word for " river". When spoken on its own, the word often means Rio de Janeiro, a major city in Brazil. Rio or Río may also refer to: Geography Brazil * Rio de Janeiro * Rio do Sul, ...

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, t ...

. According to Soria, ''Notonychops'' was a representative of a radiation of primitive South American ungulates, Notopterna, distinct from both Litopterna and

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

. Ascribed to a separate family, the Notonychopidae, ''Notonychops'' was thought to be related to other basal South American ungulates, such as '' Amilnedwardsia'' and ''Indalecia''. However, modern authors places ''Notonychops'' and its relative ''

Requisia ''Requisia'' is an extinct genus of litoptern from the Early Paleocene of Argentina. Its fossilized remains were found in the Salamanca Formation in the Chubut Province. It is a monotypic genus, its only known species being ''Requisia vidmari''. ...

'' within Litopterna, albeit in a family of their own.

Bibliography

*M. F. Soria. 1989. Notopterna: un nuevo orden de mamíferos ungulados eógenos de América del Sur. II: Notonychops powelli gen. et sp. nov (Notonychopidae nov.) de la Formación Río Loro (Paleoceno medio), provincia de Tucumán, Argentina. Ameghiniana 25(3):259-272 *J. F. Bonaparte and J. Morales. 1997. Un primitivo Notonychopidae (Litopterna) del Paleoceno inferior de Punta Peligro, Chubut, Argentina. Estudios Geológicos 53(5-6):263-274 {{Taxonbar, from=Q10337707 Litopterns Paleocene mammals of South America Paleogene Argentina Fossils of Argentina Fossil taxa described in 1989 Prehistoric placental genera