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.

Hyracotherium was recently found to be a paraphyletic group of species, and the genus now includes only H. leporinum.

[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.