The horse dates back 30 million years further than man.
It's earliest form, Hyracotherium, looked nothing like a modern horse. It stood about 30cm (12in) tall, had four toes on it's forefeet and three on it's hind, and faintly looked like a fox terrior.
It is fairly certain, from the vast numbers of fossilized bones found in the southern United states, that Hyracothrium originated in that part of the world, and there is also evidence that, before the Berling Strait split the Far West from the Far East, it wandered across into Asia and Europe.
Hyracotherium is more commonly called Eohippus, meaning "the dawn horse". It was last seen alive on this earth - although not by man, who had not yet evolved - some 40 million years ago. It was succeeded by Orohippus and Epihippus, animals with very similar skeletal structure but with more efficient teeth. These gave way, over the next 15 million years, to the bigger Mesohippus and Miohippus, which could browse on soft plants and which had started to carry their weight on the central toe of what had, by now, become three-toed feet, and Merychippus, with longer grinding teeth.
Pliohippus, of the Lower Pliocene age, was the first fully-hooved horse. It stood entirely on it's central toe of three, with its toenail developed into a wall of hoof. It looked reasonably like a horse and, by the time that Homo sapiens first appeared, it had developed further into Equus and had grown to over 120cm(4ft)high.
Relics of Equus suggest that, like the dawn horse, it originated in North America. It migrated southward, to become South America's earliest horse, and also wandered to Asia, Europe and Africa. About 8000 years ago it became extinct as a recognisable type, but its progency in Europe, Africa and Asia, adapted in little ways to suit varying climate and terrain, became the ancestors of the modern horse. Three basic types of Equus, the Steppe, the Forest and the Plateau horses of prehistory, developed into the huge variety of Equus caballus that is known today.
The Steppe type, which is still seen in Przewalski's Horse, had a large head with long ears, a long face and a convex profile. It had a short, strong body, slender limbs, narrow hooves and a mane which stood up like a brush on a thick neck. It was alert and agile, which is doubtless why it still survives.
The Forest type was heavier than the Steppe and duller witted. It was a thickly-built horse with hooves broad enough to support it on marshy ground. Its head was broad and short, concave between the eyes and convex towards the muzzle, which helped it to browse on eye-level shoots.It had a thick, hairy coat, often with spots or stripes which merged it into the dappled shadows in which it lived. It was frightened of water, no doubt because predators lurked in the trees surrounding forest drinking places. It is now extinct, but its successors live on in today's kindly, unimaginative heavy horses.
the Plateau type, very probably the ancestor of our finer-boned horses and ponies, may still exsist in the few remaining herds of Tarpan. These animals have small, narrow heads with small ears and large eyes, lightweight bodies and long slim limbs. The shape of their hooves lies between the long narrowness of the Steppe and the broad roundness of the Forest horses. These horses are thought to be the ancestors of today's lightwieght horse and pony breeds.
Most horses have come a very long way from the three primitive types and the mordern breeds did not evolve by them selves. They were purpose-bred by man for selected qualities such as speed, robustness, strength, agility or beauty. So many breeds of horse exsist today that it is sometimes hard to tell one from another.