Orohippus

Orohippus is an extinct ancestor of the modern horse that likely evolved from Eohippus in the Eocene (about 50 million years ago). The only major differences in the two were the absence of the vestigial toes that were present in Eohippus and that the last premolar changed into a molar, giving Orohippus another grinding tooth. Also the crests on the teeth were more pronounced, indicating that Orohippus probably fed on tougher plants.