Family : Equidae
The earlier known fossils that can be assigned to the family Equidae are dated from 54 million years ago in the early Eocene. These early equids foraged on soft leaves and plants and had padded feet similar to a modern dog's with 3 or 4 toes. They were fairly small, about 10-15 inches high at the shoulder. As time progressed, they became larger, developed teeth more suited to grinding tough grasses, and lost their extra toes. Today, this family classification includes horses, donkeys, and zebras (Wikipedia, "Equidae").