''Archaeohippus'' (Greek: "ancient" (archaios), "horse" (hippos)) 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 ...

three toed member of the family

Equidae Equidae (sometimes known as the horse family) is the taxonomic family of horses and related animals, including the extant horses, asses, and zebras, and many other species known only from fossils. All extant species are in the genus '' Equus'', ...

known from fossils of early

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

to middle

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

age. The genus is noted for several distinct

skeletal A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

features. The skull possesses deeply pocketed

fossa Fossa may refer to: Animals * Fossa (animal), the common name of a carnivoran mammal of genus ''Cryptoprocta'' endemic to Madagascar * ''Fossa'', the Latin genus name of the Malagasy civet, a related but smaller mammal endemic to Madagascar Pla ...

in a notably long preorbital region. The genus is considered an example of

phyletic dwarfism Phyletic dwarfism is the decrease in average size of animals of a species. There are a few circumstances that often lead to species doing this. Lack of predators of smaller creatures can allow smaller members of a species to survive. The lack of r ...

with adults estimated at being on average 20 kg in weight. This is in contrast to the most common equid of the period, ''

Miohippus ''Miohippus'' (meaning "small horse") was a genus of prehistoric horse existing longer than most Equidae. ''Miohippus'' lived in what is now North America from 32 to 25 million years ago, during the late Eocene to late Oligocene. ''Miohippus'' w ...

''. Characters of the teeth show a mix of both primitive and advanced traits. The advanced traits are very similar to those shown in the genus ''

Parahippus ''Parahippus'' ("near to horse"), is an extinct equid, a relative of modern horses, asses and zebras. It lived from 24 to 17 million years ago, during the Miocene epoch. It was very similar to ''Miohippus'', but slightly larger, at around tall, ...

''. The noted similarities of ''Archaeohippus'' and ''Parahippus'' show them to be descended from a common ancestor and are considered sister species.

Taxonomic history

The first species to be named was found in the Miocene Mascall Fauna of Cottonwood Creek,

Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

. Named '' Anchitherium ultimus'' the species was described in 1886 by noted

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

E. D. Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy intereste ...

during the height of the

Bone wars The Bone Wars, also known as the Great Dinosaur Rush, was a period of intense and ruthlessly competitive fossil hunting and discovery during the Gilded Age of American history, marked by a heated rivalry between Edward Drinker Cope (of the Acade ...

. During study 1906 on the Mascall formation equids, J. Gidley moved to a new genus he named ''Archaeohippus''. The strong similarity of the traits resulted in the genus being considered a subgenus of ''Parahippus'' by

W. D. Matthew William Diller Matthew Royal Society, FRS (February 19, 1871 – September 24, 1930) was a vertebrate paleontologist who worked primarily on mammal fossils, although he also published a few early papers on mineralogy, petrological geology, one on ...

in 1932. In stark contrast of opinion ''Archaeohippus'' was revalidated by D.F. Bode in 1933, and along with ''A. ultimus'', he included ''A. mourningi'' and ''A. penultimus''. ''Archaeohippus'' ranged across all of

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

. In addition to the occurrences in Florida and Oregon, fossil specimens have been found in Southern

Saskatchewan Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

. & 1993 "Biostratigraphy of the Cypress Hills Formation (Eocene to Miocene), Saskatchewan: equid types (Mammalia: Perissodactyla) and associated faunal assemblages." ''Journal of Paleontology'' 67:660–669. At the other end of its range ''Archaeohippus'' have been found as far south as the Miocene Gaillard Cut local in the former canalzone of

Panama Panama ( , ; es, link=no, Panamá ), officially the Republic of Panama ( es, República de Panamá), is a transcontinental country spanning the southern part of North America and the northern part of South America. It is bordered by Cos ...

. 2006 "North American Miocene Land Mammals from Panama" ''Journal of Vertebrate Paleontology'' 26(3):720–734 ''"Archaeohippus" stenolophus'', known from Oligocene deposits in Saskatchewan, does not belong in ''Archaeohippus'', and ''A. minimus'' is a composite of two taxa, as noted by Osborn (1918), with the P3-M1 belonging to ''A. ultimus'' and the molar and premolar belonging to a larger, more derived equid. ''Archaeohippus mannulus'' and ''Arachaeohippus blackbergi'' have been unearthed in Florida, specifically at the

Thomas Farm Site The Thomas Farm site is an Early Miocene, Hemingfordian assemblage of vertebrate fossils located in Gilchrist County, northern Florida. The Thomas Farm site is one of the richest terrestrial deposits of Miocene vertebrates in the 18 Ma range fo ...

. In at least part of its range ''Archaeohippus'' dwelt in a forested or wooded habitat.

References

{{Taxonbar, from=Q776370 Oligocene horses Miocene odd-toed ungulates Oligocene odd-toed ungulates Serravallian genus extinctions Prehistoric placental genera Cenozoic mammals of North America Chattian genus first appearances Miocene horses Fossil taxa described in 1906