Before there were horses, there was eohippus. Here’s how the little prehistorian got its start on the long road to horsehood.
Eohippus lived about 50 to 60 million years ago in the Northern Hemisphere and is believed to be the ancestor of modern horses, rhinos, and piglike mammals called tapirs. It was just two feet long and eight or nine inches high at the shoulder—about the size of a small dog. It had four hoofed toes on its front feet, three hoofed toes on each hind foot, a long skull, and 44 teeth.
Eohippus didn’t look like a horse at all. It had short legs, a short neck, pads on its toes, and an arched back. The animal made its home in European and North American forests, where its diet consisted mostly of leaves. Over time, though, the Earth’s forests started to shrink, and grasslands spread. So eohippus wandered out into the open and started to nibble on grass.
Plants have to evolve to survive, too, though, so over the next few million years, some of them developed strategies to prevent them from being eaten. In particular, one of eohippus’s main food sources, the “lallang” grasses, developed jagged grains of sand called silica in their leaves. That wore down the eohippus’ teeth, so some of the horses died off. The ones who had bigger teeth with thicker enamel lived long enough to reproduce. In turn, their offspring developed longer faces with stronger jaws to make even better use of those big, strong teeth.
But while the horses were out there out on the wide-open grasslands, they were easy pickings for predators. So the animals had to be speedy to survive. New generations were longer-legged, faster, stronger, and had fewer toes, until they evolved into the look and size of modern horses.
In 1841, an English paleontologist named Richard Owen found the first evidence of eohippus: a tooth and part of a jawbone. He suspected it was a horse ancestor because of the tooth, but others initially thought the fossils belonged to a monkey and concluded (incorrectly) that England must have once been a jungle. Over time, though, other scientists figured out that they didn’t come from monkeys at all, but from small horses.
Then, in 1867, American paleontologists dug up the first complete eohippus skeleton in western Wyoming. A few years later, scientist Othniel C. Marsh named the creature eohippus (or “dawn horse”). The Wyoming find finally revealed a true picture of the horse’s earliest relative.