This order is comprised of odd-toed hoofed mammals including horses, rhinos, and tapirs. In past geologic times its members were made more numerous and widespread than they are today.

This family contains seven species including horses, zebras, and wild asses.

There are at least 111 recognized breeds of domesticated horses including thoroughbreds, Suffolks, quarterhorses, Arabians, and Clydesdales.

The domesticated horse has evolved from the now extinct form Eohippus, first recorded about 40 million years ago during the Eocene period. Eohippus was a small foxlike animal, also known as the dawn horse.

Some scientists believe that domesticated horses are descendents of the Przewalski's horse (Equus przewalskii).