Eohippus Temporal range: Ypresian, | |
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Reconstructed skeleton, National Museum of Natural History, Washington, D.C., United States | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Perissodactyla |
Family: | Equidae |
Genus: | † Eohippus Marsh, 1876 |
Species: | †E. angustidens |
Binomial name | |
†Eohippus angustidens (Cope, 1875) | |
Synonyms | |
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Eohippus is an extinct genus of small equid ungulates. [1] The only species is E. angustidens, which was long considered a species of Hyracotherium (now strictly defined as a member of the Palaeotheriidae rather than the Equidae). Its remains have been identified in North America and date to the Early Eocene (Ypresian stage). [2]
In 1876, Othniel C. Marsh described a skeleton as Eohippus validus, from Greek : ἠώς (eōs, 'dawn') and ἵππος (hippos, 'horse'), meaning 'dawn horse'.[ citation needed ] Its similarities with fossils described by Richard Owen were formally pointed out in a 1932 paper by Clive Forster Cooper. E. validus was moved to the genus Hyracotherium , 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 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, [3] and the resulting binomial is thus Eohippus angustidens.
Eohippus stood at about 12 in (30 cm), or three hands tall, at the shoulder. [4] It has four toes on its front feet and three toes on the hind feet, 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. [4] [5]
In his 1991 essay, "The Case of the Creeping Fox Terrier Clone", [6] Stephen Jay Gould lamented the prevalence of a much-repeated phrase to indicate Eohippus size ("the size of a small Fox Terrier"), 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, and proposed that Osborn, a keen fox hunter, could have made a natural association between his horses and the dogs that accompanied them. [6]