• WordNet 3.6
    • n protohippus Pliocene horse approaching donkeys in size
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Webster's Revised Unabridged Dictionary
    • n Protohippus (Paleon) A genus of fossil horses from the Lower Pliocene. They had three toes on each foot, the lateral ones being small.
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Century Dictionary and Cyclopedia
    • n protohippus A genus of fossil horses of the family Equidæ, founded by Leidy in 1858 upon remains from the early Pliocene of North America.
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Webster's Revised Unabridged Dictionary
NL., from Gr. first + horse


In literature:

Miohippus, Protohippus, and Hypohippus, varying in size from that of a sheep to that of a donkey, are other branches of this spreading family.
"The Story of Evolution" by Joseph McCabe
These he names, Hipparion, Protohippus, Merychippus, Hypohippus, and Parahippus.
"The Geological Evidence of The Antiquity of Man" by Charles Lyell
This animal lived in Europe while the Pliohippus and the Protohippus were flourishing in America.
"Earth and Sky Every Child Should Know" by Julia Ellen Rogers