Orohippusn.

1877 J. W. Dawson Origin of World x. 227 The earliest of them, the Orohippus, would require, on the theory, to have been preceded by a previous series.

?1877 J. B. Holder Hist. Amer. Fauna in J. Richardson et al. Museum Nat. Hist. (new ed.) p. cxiii/1 Several species, about the size of a Fox, have been found in the Eocene of Utah and Wyoming. These have four toes before, and three behind. The last-mentioned are included in the genus Orohippus.

1931 Science 11 Sept. 261/1 The four-toed horse called Orohippus which lived approximately 55,000,000 years ago.

1966 A. S. Romer Vertebr. Paleontol. (ed. 3) xxiii. 266/1 In the middle and Upper Eocene of North America we find, in Orohippus and Epihippus, descendants of this equid in which the structures are the same.

1993 Science (Nexis) 21 May 1156 If we start with the familiar still-living Equus and work backward to little Eohippus..at the beginning of the Eocene, we get a long line of names: Equus, Merychippus, Parahippus, Miohippus, Mesohippus, Epihippus, Orohippus, Eohippus.