In our modern consciousness, horses only look one way: tall, with flat backs, long heads, and four hooves. The modern horse has had a long evolution, however, one that takes it from the plains east of America’s Sierra mountains, to Eurasia, and back again, over the course of 70 million years. Here is an overview of our understanding of horse evolution, based on the fossil record.
70-55 Million Years Ago
The first equid, or horse ancestor, came onto the scene about 70 million years ago. This little guy was known as an Eocene horse, and he only stood about 10-20” tall at the shoulder! It had a rounded back like a dog, although all the major bone structure of the modern horse was present as well. It enjoyed munching on soft leaves, grasses, and fruit, and was not all that different from tapirs and rhinos, two species that are ancestral to the modern horse.
Over a span of 20 million years, the Eocene horse went through two distinct stages, evolving to the Orohippus and the Epihippus relatives. During this time, the teeth of the horse changed, shaping into a few grinding molars that allowed it to eat tougher food.
40-25 Million Years Ago
A lot was happening during this period in America, and early horses went through many corresponding changes. As the vast forestland of America began to shrink during the Oligocene period, grasslands appeared, and horses began changing.
Mesohippus came on the scene about 40 million years ago. Unlike its earlier ancestors, Mesohippus was a little taller (24” at shoulder height), with longer legs and a less-arched back. Its brain got bigger, and its teeth evolved into the basic structure that we recognize in modern horses today, with six grinding teeth.
25-17 Million Years Ago
As horses started munching on the new American plains, evolutionary changes were happening. Their teeth developed grooves that were better for chewing up tough foliage. Their bodies elongated, and the bones in their legs became fused together. They started using their tip-toes to run more quickly, and began running less on the pads of their feet, in a dog-like manner.
17-5 Million Years Ago
This period represented a huge milestone in horse evolution. During this time, much branching of the evolutionary tree occurred, creating several different horse varieties. Amongst these varieties were “one-toed horses”, horses that were developing a foot that would be a progenitor to our modern horse’s hoof. This single toe helped keep the horse steady while running across the plains.
5 Million Years Ago-Present
About 5 million years ago Equus, the grandfather of our modern horse, finally arrived. Equus was still rather small, at about the size of a pony, but he had all the shaping of a modern horse. He had a larger brain, long limbs, a long nose, one toe on each foot, and a deep jaw. Equus became the dominant variety of horse, and its three-toed cousins died out.
About 1 million years ago, different types of Equus could be found in huge migrating herds across very major continent. 3,000 years ago, Equus became domesticated by humans, beginning the legacy of modern horse breeding we know today.