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Definition of Protohippus
1. Noun. Pliocene horse approaching donkeys in size. 
Definition of Protohippus
1. n. 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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1. Noun. Pliocene horse approaching donkeys in size. 
1. n. A genus of fossil horses from the Lower Pliocene. They had three toes on each foot, the lateral ones being small.