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''Eohippus'' is an
In 1876, Othniel C. Marsh described a skeleton as ''Eohippus validus'', from (, 'dawn') and (, 'horse'), meaning 'dawn horse'. Its similarities with fossils described by
extinct
Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of small equid
Equidae (commonly known as the horse family) is the Taxonomy (biology), taxonomic Family (biology), family of Wild horse, horses and related animals, including Asinus, asses, zebra, zebras, and many extinct species known only from fossils. The fa ...
ungulate
Ungulates ( ) are members of the diverse clade Euungulata ("true ungulates"), which primarily consists of large mammals with Hoof, hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined ...
s. The only species is ''E. angustidens'', which was long considered a species of ''Hyracotherium
''Hyracotherium'' ( ; "hyrax-like beast") is an extinction, extinct genus of small (about 60 cm in length) perissodactyl ungulates that was found in the London Clay formation. This small, fox-sized animal is (for some scientists) considered t ...
'' (now strictly defined as a member of the Palaeotheriidae
Palaeotheriidae is an extinct family of herbivorous perissodactyl mammals that inhabited Europe, with less abundant remains also known from Asia, from the mid-Eocene to the early Oligocene. They are classified in Equoidea, along with the livin ...
rather than the Equidae). Its remains have been identified in North America and date to the Early Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
(Ypresian
In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...
stage).
Discovery
In 1876, Othniel C. Marsh described a skeleton as ''Eohippus validus'', from (, '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 anatomy, comparative anatomist and paleontology, palaeontologist. Owen is generally considered to have been an outstanding naturalist with a remarkabl ...
were formally pointed out in a 1932 paper by Clive Forster Cooper. ''E. validus'' was moved to the genus ''Hyracotherium
''Hyracotherium'' ( ; "hyrax-like beast") is an extinction, extinct genus of small (about 60 cm in length) perissodactyl ungulates that was found in the London Clay formation. This small, fox-sized animal is (for some scientists) considered t ...
'', 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
Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
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 is thus ''Eohippus angustidens''.
Description
''Eohippus'' stood at about , or three hands tall, at the shoulder. 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.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 Paleontology, paleontologist, Evolutionary biology, evolutionary biologist, and History of science, historian of science. He was one of the most influential and widely re ...
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 United Kingdo ...
"), 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.
See also
*Evolution of the horse
The evolution of the horse, a mammal of the family Equidae, occurred over a geologic time scale of 50 million years, transforming the small, dog-sized, forest-dwelling '' Eohippus'' into the modern horse. Paleozoologists have been able to piece ...
- more broad info on the topic
*'' Mesohippus''
*''Protohippus
''Protohippus'' is an extinct three-toed genus of horse. It was roughly the size of a modern donkey. Fossil evidence suggests that it lived during the Late Miocene (Clarendonian to Hemphillian
The Hemphillian North American Stage on the geologic ...
''
References