The Evolution of the Horse

The development of the horse is one of the best known of the evolutionary stories. The early ancestor of the horse was called hyracotherium. It was only about 30 centimetres high. Hyracotherium lived in Europe and North America about 50 million years ago in the Lower Eocene. It had four small toes on each of its front feet and three on each of its back feet. These toes were more flexible than single ones would have been. They probably helped the animal to travel over the soft uneven ground in the forest glades where it lived, feeding on the leaves of shrubs.

Horses the size of dogs

Within another 15 million years, in the oligocene, a later horse, mesohippus, about the size of a collie dog, had replaced hyracotherium. It had three toes on each foot but the centre one was large, whereas the side toes on each foot were much smaller. This arrangement probably made mesohippus faster than hyracotherium had been.

By 15 million years ago, the horse was about the size of an alsatian dog. merychippus, as it is called, still had three toes on each foot, but its side toes were even smaller while the centre toe was very large. Some parts of the earth had been rising and growing drier and colder. Merychippus had left the forests, which were dwindling, and had taken to the wide grassy plains. Its teeth were longer and better suited for eating grass. Its long legs were more fitted for running, for which the large middle toe, used as a hoof, was ideally suited.

Stages in the evolution of the horse

Present-day horses

So the process went on. Gradually the horse changed and grew larger. The side toes disappeared and, about a million and a half years ago, the horse became the animal we know today, large, speedy and strong, an animal of the open countryside which needed to be able to run fast to escape from its enemies.