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''Orohippus'' (Gr., "mountain horse") is an extinct equid that lived in the Eocene (about 50 million years ago). It is believed to have evolved from equids such as ''Eohippus'', as the earliest evidence for ''Orohippus'' appears about 2 million years after the first appearance of ''Eohippus''. The anatomical differences between the two are slight: they were the same size, but ''Orohippus'' had a slimmer body, a more elongated head, slimmer forelimbs and longer hind legs, all of which are characteristics of a good jumper. The upper premolars of ''Orohippus'' are more molariform (flat-surfaced) than in ''Eohippus'', giving ''Orohippus'' more teeth for grinding, and the crests on the teeth are more pronounced, indicating that ''Orohippus'' probably fed on tougher plants. The outer toes of ''Eohippus'' are no longer present in ''Orohippus'', hence on each forelimb there were four fingers (toes) and on each hind leg three toes. Species of ''Orohippus'' has also been referred to ''Protorohippus''. ==See also== * Evolution of the horse * Horse 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Orohippus」の詳細全文を読む スポンサード リンク
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