''Rhynchippus'' ("Snout Horse") 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 nom ...

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 ...

mammals from the

Late Oligocene The Chattian is, in the geologic timescale, the younger of two ages or upper of two stages of the Oligocene Epoch/ Series. It spans the time between . The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stage ...

( Deseadan in the SALMA classification) of South America. The genus was first described by

Florentino Ameghino Florentino Ameghino (born Giovanni Battista Fiorino Giuseppe Ameghino September 19, 1853 – August 6, 1911) was an Argentine naturalist, paleontologist, anthropologist and zoologist, whose fossil discoveries on the Argentine Pampas, especially ...

in 1897 and the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

is ''R. equinus'', with

lectotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...

MACN A 52–31. Fossils of ''Rhynchippus'' have been found in the Agua de la Piedra and Sarmiento Formations of

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 ...

, the

Salla Salla (''Kuolajärvi'' until 1936) ( smn, Kyelijävri) is a municipality of Finland, located in Lapland. The municipality has a population of () and covers an area of of which is water. The population density is . The nearby settlement of ...

and Petaca Formations of Bolivia, the

Tremembé Formation Tremembé is a municipality in the state of São Paulo in Brazil. It is part of the Metropolitan Region of Vale do Paraíba e Litoral Norte. The population is 47,714 (2020 est.) in an area of 191.09 km². The elevation is 560 m. A shr ...

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 ...

,''Rhynchippus''
at Fossilworks.org and the Moquegua Formation of

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 ...

Description

''Rhynchippus'' was about in length and weighed up to , with a deep body and three clawed toes on each foot.Patterson & Pires Costa, 2012, p.83 Although its

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, t ...

were extremely similar to those of

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million yea ...

s or rhinos, ''Rhynchippus'' was actually a relative of ''

Toxodon ''Toxodon'' (meaning "bow tooth" in reference to the curvature of the teeth) is an extinct genus of South American mammals from the Late Miocene to early Holocene epochs (Mayoan to Lujanian in the SALMA classification) (about 11.6 million to 1 ...

'', having developed teeth suitable for

grazing In agriculture, grazing is a method of animal husbandry whereby domestic livestock are allowed outdoors to roam around and consume wild vegetations in order to convert the otherwise indigestible (by human gut) cellulose within grass and other ...

through

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

. Unlike its relatives, ''Rhynchippus'' had no large tusks; they were the same size and shape as the

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

s. Enamel on the

molars The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...

allowed it to chew tough food.Palmer et al., 1999, p.252 The genus shows similarities with '' Mendozahippus'', '' Eurygenium'' and '' Pascualihippus''. In

2016 File:2016 Events Collage.png, From top left, clockwise: Bombed-out buildings in Ankara following the 2016 Turkish coup d'état attempt; the Impeachment of Dilma Rousseff, impeachment trial of Brazilian President Dilma Rousseff; Damaged houses duri ...

, a well-preserved specimen of ''R. equinus'' was described by Martínez et al. from the Sarmiento Formation in central

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...

. The extraordinary preservation of the specimen allowed the researchers to appreciate the three connected spaces that constitute a heavily pneumatized middle ear; the epitympanic sinus, the tympanic cavity itself, and the ventral expansion of the tympanic cavity through the notably inflated bullae.

Paleoecology

Fossils of ''Rhynchippus'' have been found in various fossiliferous stratigraphic units in South America, all restricted to the Deseadan

South American land mammal age The South American land mammal ages (SALMA) establish a geologic timescale for prehistoric South American fauna beginning 64.5 Ma during the Paleocene and continuing through to the Late Pleistocene (0.011 Ma). These periods are referred to as age ...

. Several specimens come from the Sarmiento Formation in the

Golfo San Jorge Basin The Golfo San Jorge Basin ( es, Cuenca del Golfo San Jorge) is a hydrocarbon-rich sedimentary basin located in eastern Patagonia, Argentina. The basin covers the entire San Jorge Gulf and an inland area west of it, having one half located in San ...

in central

, with other finds from the Petaca Formation of the Subandean Belt in Bolivia, the Salla Formation from the same country, the Moquegua Formation of the Moquegua Basin in southern

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 ...

, the Agua de la Piedra Formation of the

Neuquén Basin Neuquén Basin ( es, Cuenca Neuquina) is a sedimentary basin covering most of Neuquén Province in Argentina. The basin originated in the Jurassic and developed through alternating continental and marine conditions well into the Tertiary. The bas ...

in Argentina, and the

of the

Taubaté Basin Taubaté is a medium-sized city in the State of São Paulo, in southeastern Brazil. Location Its strategic location between the two most important Brazilian cities (São Paulo away, and Rio de Janeiro away), connected to both by the Presiden ...

in eastern

. The Sarmiento and Salla Formations have provided a rich assemblage of many mammals and

terror birds Phorusrhacids, colloquially known as terror birds, are an extinct clade of large carnivorous flightless birds that were one of the largest species of apex predators in South America during the Cenozoic era; their conventionally accepted tempor ...

, as '' Physornis''. The faunal assemblage of ''Rhynchippus'' fossil locations also constitutes several

crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest livi ...

ns, snakes ('' Madtsoia''), helmeted bull frogs, a catfish; '' Taubateia paraiba'', and the

caiman A caiman (also cayman as a variant spelling) is an alligatorid belonging to the subfamily Caimaninae, one of two primary lineages within the Alligatoridae family, the other being alligators. Caimans inhabit Mexico, Central and South America f ...

'' Caiman tremembensis''. The Tremembé Formation is known for the preservation of several insects.

Gallery

Notes and references

Notes

References

Bibliography

* * * {{Taxonbar, from=Q911486 Toxodonts Chattian life Oligocene mammals of South America Deseadan Paleogene Argentina Fossils of Argentina Golfo San Jorge Basin Paleogene Bolivia Fossils of Bolivia Paleogene Brazil Fossils of Brazil Paleogene Peru Fossils of Peru Fossil taxa described in 1897 Taxa named by Florentino Ameghino Prehistoric placental genera Sarmiento Formation