''Hippidion'' (meaning ''little horse'') is an extinct genus of

equine Equinae is a subfamily of the family Equidae, which have lived worldwide (except Indonesia and Australia) from the Hemingfordian stage of the Early Miocene (16 million years ago) onwards. They are thought to be a monophyletic grouping.B. J. Ma ...

that lived in South America from the Late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Late Pleistocene The Late Pleistocene is an unofficial age in the international geologic timescale in chronostratigraphy, also known as Upper Pleistocene from a stratigraphic perspective. It is intended to be the fourth division of the Pleistocene Epoch withi ...

( Lujanian), between two million and 11,000 years ago. They were one of two lineages of equines native to South America during the Pleistocene epoch, alongside those of the '' Equus'' subgenus ''

Amerhippus ''Amerhippus'' is an extinct South American horse of uncertain taxonomic identity. It is sometimes classified as a subgenus of the genus '' Equus'', containing several extinct species of horses that lived in South America, or a single, morphologi ...

''.

Evolution

''Hippidion'' has been considered a descendant of pliohippines, equines that migrated into the South American continent around 2.5 million years ago. Early analysis of the

ancient DNA Ancient DNA (aDNA) is DNA isolated from ancient specimens. Due to degradation processes (including cross-linking, deamination and fragmentation) ancient DNA is more degraded in comparison with contemporary genetic material. Even under the bes ...

of ''Hippidion'' and other

New World The term ''New World'' is often used to mean the majority of Earth's Western Hemisphere, specifically the Americas."America." ''The Oxford Companion to the English Language'' (). McArthur, Tom, ed., 1992. New York: Oxford University Press, p. ...

Pleistocene equines supported the novel hypothesis that ''Hippidion'' was actually a member of the living genus '' Equus'', with a particularly close relationship to the

wild horse The wild horse (''Equus ferus'') is a species of the genus ''Equus'', which includes as subspecies the modern domesticated horse (''Equus ferus caballus'') as well as the endangered Przewalski's horse (''Equus ferus przewalskii''). The Europea ...

, ''Equus ferus''. However this was later shown to be incorrect, with more complete sequences finding ''Hippidion'' as an outgroup to all living equines and less closely related to living equines than the "New World stilt legged horse", '' Haringtonhippus francisci.'' Hippidion is traditionally thought to have 3 species, ''H. principale, H. saldiasi'' and ''H. devillei'', however, in a 2015 DNA analysis, the single sampled ''H. principale'' specimen was found to be nested with ''H. saldiasi'', with ''H. devillei'' found to be clearly genetically distinct. ''Hippidion'' and other South American equines became extinct approximately 8,000 years ago. Specific

archaeological Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...

recovery at the

Cueva del Milodon Cuevas or Cueva (Spanish for "''cave(s)''") may refer to: Places * Cueva de Ágreda, a municipality located in the province of Soria, Castile and León, Spain * Cuevas Bajas, a town and municipality in the province of Málaga, part of the autonom ...

site in

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 ...

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...

demonstrates that ''Hippidion saldiasi'' existed in that vicinity in the era of 10,000 to 12,000 years before present, making it the last surviving member of its species. Equines did not reappear in South America until the 16th century, as a result of introduction by humans.

Description

It stood approximately (also 13.2 hh) high at the shoulders and resembled a

donkey The domestic donkey is a hoofed mammal in the family Equidae, the same family as the horse. It derives from the African wild ass, ''Equus africanus'', and may be classified either as a subspecies thereof, ''Equus africanus asinus'', or as ...

. The skull of ''Hippidion'' is noted for its

nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Ea ...

, which projects forward from the skull.

Diet and ecology

A study found that Late Pleistocene specimens of ''Hippidion'' had lower ''δ¹³C'' values than those of specimens of ''Amerhippus'', indicating a preference for C3 woodland and wooded open habitats. ''H. principale'' is suggested to have been a mixed feeder (both

browsing Browsing is a kind of orienting strategy. It is supposed to identify something of relevance for the browsing organism. When used about human beings it is a metaphor taken from the animal kingdom. It is used, for example, about people browsing o ...

and

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 ot ...

), as opposed to the grazing diet of the contemporary '' Equus neogeus.''

Discovery

Remains of ''Hippidion saldiasi'' have been recovered in locations such as the

Piedra Museo Piedra Museo is an archaeological site in Santa Cruz Province, Argentina, and one of the earliest known archaeological remains in the Americas. Overview The site was discovered around 1910 by Argentine naturalist Florentino Ameghino, who wrote t ...

site, Santa Cruz, Argentina and

. The significance of such

recovery is amplified by the association with hunting of these animals by

prehistoric Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The us ...

man at possible Pre-Clovis horizons.

Distribution

Fossils of ''Hippidion'' have been found in:''Hippidion''
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was crea ...

.org ;Pleistocene *

Tarija Tarija or San Bernardo de la Frontera de Tarixa is a city in southern Bolivia. Founded in 1574, Tarija is the largest city and capital and municipality within the Tarija Department, with an airport ( Capitán Oriel Lea Plaza Airport, (TJA)) off ...

, Ñuapua and Ulloma Formations,

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

* Jandaíra Formation,

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 ...

* Chíu-Chíu Formation, Cueva del Milodón,

Tierra del Fuego Tierra del Fuego (, ; Spanish for "Land of the Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of the main island, Isla ...

, Magallanes Province and its borders with

Argentine Argentines (mistakenly translated Argentineans in the past; in Spanish (masculine) or (feminine)) are people identified with the country of Argentina. This connection may be residential, legal, historical or cultural. For most Argentines, ...

* Sopas and Dolores Formations,

Uruguay Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...

Taima-Taima Taima-Taima is a Late Pleistocene archaeological site located about 20 kilometers east of Santa Ana de Coro, in the Falcón State of Venezuela. The human settlement at Taima-Taima started about 14,000 years ago. History of research The site was ...

Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...

Extinction

''Hippidion'' became extinct alongside the other South American equines at the end of the Late Pleistocene, between 15,000 and 10,000 years ago as part of the

Quaternary extinction event The Quaternary period (from 2.588 ± 0.005 million years ago to the present) has seen the extinctions of numerous predominantly megafaunal species, which have resulted in a collapse in faunal density and diversity and the extinction of key ecolog ...

, which resulted in the extinction of most large animals in both North and South America. Climatic modelling suggests that the preferred habitat for species of ''Hippidion'' declined after the Holocene transition, but the decline is not enough to explain the extinction.

References

{{Taxonbar, from=Q133193 Pliocene horses Pleistocene horses Pliocene first appearances Pleistocene genus extinctions Prehistoric placental genera Pleistocene mammals of South America Pliocene mammals of South America Uquian Ensenadan Lujanian Pleistocene Argentina Fossils of Argentina Pleistocene Bolivia Fossils of Bolivia Pleistocene Brazil Fossils of Brazil Pleistocene Chile Fossils of Chile Pleistocene Uruguay Fossils of Uruguay Pleistocene Venezuela Fossils of Venezuela Fossil taxa described in 1869