''Eohippus'' 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 living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of small

equid 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' ...

ungulate Ungulates ( ) are members of the diverse clade Ungulata which primarily consists of large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses, and tapirs; and even-toed ungulates such as cattle, pigs, giraffes, ...

s. The only species is ''E. angustidens'', which was long considered a species of ''

Hyracotherium ''Hyracotherium'' ( ; "hyrax-like beast") is an extinct genus of very small (about 60 cm in length) perissodactyl ungulates that was found in the London Clay formation. This small, fox-sized animal was once considered to be the earliest know ...

''. Its remains have been identified in North America and date to the Early

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...

(

Ypresian In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by the Eocene Lutetian Age. The Ypresian ...

stage).

Discovery

In 1876,

Othniel C. Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among h ...

described a skeleton as ''Eohippus validus'', from el, ἠώς (, 'dawn') and (, 'horse'), meaning 'dawn horse'. Its similarities with fossils described by

Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils. Ow ...

were formally pointed out in a 1932 paper by

Clive Forster Cooper Sir Clive Forster Cooper, FRS (3 April 1880 – 23 August 1947) was an English palaeontologist and Director of the Cambridge University Museum of Zoology and Natural History Museum in London. He was the first to describe ''Paraceratherium'', als ...

. ''E. validus'' was moved to the genus ''

'', which had priority as the name for the genus, with ''Eohippus'' becoming a junior synonym of that genus. ''Hyracotherium'' was recently found to be a

paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

group of species, and the genus now includes only ''H. leporinum''. ''E. validus'' was found to be identical to an earlier-named species, ''Orohippus angustidens'' Cope, 1875, and the resulting

binomial Binomial may refer to: In mathematics *Binomial (polynomial), a polynomial with two terms *Binomial coefficient, numbers appearing in the expansions of powers of binomials *Binomial QMF, a perfect-reconstruction orthogonal wavelet decomposition * ...

is thus ''Eohippus angustidens''.

Description

''Eohippus'' stood at about 12 in (30 cm), or 3 hands tall. It had 4 toes on its front feet and 3 toes on the hinds, each toe ending in a hoof. Its incisors, molars and premolars resemble modern ''Equus'', however a differentiating trait of ''Eohippus'' is its large canine teeth.

Stephen Jay Gould comments

In his 1991 essay, "The Case of the Creeping Fox Terrier Clone",

Stephen Jay Gould Stephen Jay Gould (; September 10, 1941 – May 20, 2002) was an American paleontologist, evolutionary biologist, and historian of science. He was one of the most influential and widely read authors of popular science of his generation. Goul ...

lamented the prevalence of a much-repeated phrase to indicate ''Eohippus'' size ("the size of a small

Fox Terrier Fox Terriers are two different breeds of the terrier dog type: the Smooth Fox Terrier and the Wire Fox Terrier. Both of these breeds originated in the 19th century from a handful of dogs who are descended from earlier varieties of British terr ...

"), even though most readers would be quite unfamiliar with that breed of dog. He concluded that the phrase had its origin in a widely-distributed pamphlet by

Henry Fairfield Osborn Henry Fairfield Osborn, Sr. (August 8, 1857 – November 6, 1935) was an American paleontologist, geologist and eugenics advocate. He was the president of the American Museum of Natural History for 25 years and a cofounder of the American Euge ...

, and proposed that Osborn, a keen fox hunter, could have made a natural association between his horses and the dogs that accompanied them. ''Eohippus'' was approximately high at the shoulder, which would be comparable to a Fox Terrier, which is up to high at the shoulder.

References

{{DEFAULTSORT:Eohippus Eocene horses Eocene odd-toed ungulates Eocene mammals of North America Prehistoric placental genera

Discovery

Description

Stephen Jay Gould comments

See also

References