''Eoastrapostylops'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

astrapothere 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 Magdale ...

that lived during the

Late Paleocene The Thanetian is, in the International Commission on Stratigraphy, ICS Geologic timescale, the latest age (geology), age or uppermost stage (stratigraphy), stratigraphic stage of the Paleocene epoch (geology), Epoch or series (stratigraphy), Serie ...

in what is now

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 ...

Description

This animal was small in size; the skull was 9 centimeters long and the total length of the animal probably just exceeded half a meter. ''Eoastrapostylops'' possessed a short muzzle ; its canines were well developed but not yet derived into large fangs, as was the case in later South American ungulates such as ''

Trigonostylops ''Trigonostylops'' is an extinct genus of South American meridiungulatan ungulate, from the Late Paleocene to Late Eocene (Itaboraian to Tinguirirican in the SALMA classification) of South America (Argentina and Peru) and Antarctica (Seymour Isla ...

'', and the nasal bones were not retracted, indicating the absence of the typical

proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...

exhibited by later forms. The dentition of ''Eoastrapostylops'' recalls that of its later relative, ''Trigonostylops''. 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 were low-crowned and lophoselenodont-shaped. The fourth premolar was molarized, while both the fourth upper premolar and the third upper molar were triangularly shaped and lacked an hypoconus.

Classification

''Eoastrapostylops riolorense'' was first described in 1981, based on fossils found in 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, a ...

, in the Tucuman Province of

. The authors immediately identified the traits of a primitive

, and therefore established the family Eoastrapostylopidae. More recent researches have brought to light notable similarities between the auditory regions of ''Eoastrapostylops'' and those of archaic "

condylarth Condylarthra is an informal group – previously considered an order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates. It is now largely considered to be a wast ...

s" and

litoptern 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 th ...

s. Those researches would indicate that ''Eoastrapostylops'' was one of the most basal member of the South American ungulates, and differentiated before the separation between astrapotheres, pyrothere and

notoungulate 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 resemb ...

s.*A. G. Kramarz, M. Bond, and G. W. Rougier. 2017. Re-description of the Auditory Region of the Putative Basal Astrapothere (Mammalia) Eoastrapostylops riolorense Soria and Powell, 1981. Systematic and Phylogenetic Considerations. Annals of Carnegie Museum 84(2):95-164

References

*M. F. Soria and J. E. Powell. 1981. Un primitivo Astrapotheria (Mammalia) y la edad de la Formación Río Loro, provincia de Tucumán, República Argentina. Ameghiniana 18(3-4):155-168 *Soria, M. F. 1987. Estudios sobre los Astrapotheria (Mammalia) del Paleoceno y Eoceno. Parte I: Descripcion de Eoastrapostylops riolorense Soria y Powell, 1982. Ameghiniana 24:21–34. *Cifelli, R. L. 1993. The phylogeny of the native South American ungulates; pp. 195–216 in F. S. Szalay, M. J. Novacek, and M. C. McKenna (eds.), Mammal Phylogeny: Placentals. Springer-Verlag, New York. {{Taxonbar, from=Q30894648 Meridiungulata Paleocene mammals of South America Paleogene Argentina Fossils of Argentina Peligran Fossil taxa described in 1981 Prehistoric placental genera