Equine Evolution (PP)

Modern horses have evolved to be adapted for environments very different to those the first equines lived in, and horses as we know them today look nothing like their earliest ancestors did when they first appeared. The first horse-like creature lived in North America and Europe about 54 million years ago, during the Eocene. Unlike modern horses, Hyracotherium boreale (also called Eohippus) was adapted for life in the woodlands and forests that dominated the Eocene. Hyracotherium was much smaller than the modern horse, and it had an arched back and raised hindquarters, a short snout, and a small cranium. It had short legs that ended in padded feet, four-toed forefeet and three-toed hind feet, and a functional hoof on each toe. Hyracotherium was a browsing animal that fed on shrubs, leaves, and branches, as evidenced by its low-crowned teeth and distinctive molars that were designed for grinding.

During the Oligocene, environmental changes occurred that started to change the local flora, and so about 33 million years ago Mesohippus bairdi appeared. Although also a forest browser, Mesohippus had a longer face and snout than Hyracotherium did, and had developed premolars that were more complex and had defined cusps. Mesohippus had three toes on both its fore and hind feet, as the fourth toe previously found on Hyracotherium was reduced to a vestigial nub, and unlike Hyracotherium Mesohippus had longer legs and a relatively straight and stiff spine that enabled it to run over hard ground.