The evolution of Horse

     Among many different fossilized mammals, the Horse is perhaps the one whose evolutionary process is the most well known and well supported by abundant fossils found in North America, South America and Europe. The oldest common ancestor of Horse is known to be Eohippus, a fox-sized mammal that lived in the woods of North America 58 million years ago. Eohippus was in fact very different from the modern day horse: its forefoot and hindfoot had four and three toes respectively, and its height didn't exceed 1 feet. As Eohippus evolved into Orohippus and Epihippus, its body size significantly increased and its number of toes became three, but it was not until 36 million years ago that the Mesohippus appeared, resembling the modern day horse with its unprecedented hoof. The number of toes decreased into one 13 million years ago along with the advent of Philohippus, and 10 million years later eventually appeared Equus, which is congeneric to the modern day horse.
     The evolution of horse shows a consistent tendency towards a decrease in the number of toes, increase in the body size, and enlargement of the cerebrum.