from The Century Dictionary.
- noun A genus of fossil horses or Equidæ from the Pliocene of North America.
- noun [lowercase] A horse of this genus.
from the GNU version of the Collaborative International Dictionary of English.
- noun (Paleon.) An extinct genus of horses from the Pliocene deposits. Each foot had a single toe (or hoof), as in the common horse.
Sorry, no etymologies found.
One of the biggest changes in the antecedents of the horse appeared about six million years ago, when pliohippus, the latest in the breed, evolved with only one toe on each foot and with the pads on which his ancestors had run eliminated.
"Paleohippus, " of the many capacities, eohippus of the subtle form, merychippus with the horse-like appearance, pliohippus with the single hoof'these attributes persisted; there were dozens of other variations equally interesting which died out because they did not contribute to the final form.