How Horses have Evolved
Ancestors of the Equus Family
Eohippus
Fossil evedence has shown that the earliest known ancestor of our modern day horse lived about 55 million years ago during the early Eocene period. They lived in the forests of the American continent that was joined to the European continent at the time. They were a small creature, about the size of a fox, and walked with four toes on their front legs and three on their back. They were called "Hyracotherium" but are more commonly known as "Eohippus" or "the dawn horse."
Orohippus
Co-existing with the Eohippus, the Orohippus evolved. Like the Eohippus, it had toes and was the same size as it making them practicaly identical, with the acception of one difference. The Orohippus had different teeth to the Eohippus; the new teeth could give alot more grinding action meaning that some of the Eohippus started eating tougher plant material than before.
Eppihippus
Still the same shape and size of its ancestors, however with an extra tooth giving the Eppihippus five grinding teeth in total.
Mesohippus
During the very beginning of the Oligocene period, North Americas climate was changing. Forests started to give way creating more grassy areas, and the weather became alot drier. Due to the climate change, the Eppihippus evolved into the Mesohippus so it could survive in the drier and more open area. It grew larger in size with a straighter back and longer head,neck and legs (now with three toes on all legs) allowing it to run alot quicker. It also grew another tooth to help it eat the new grass better.