Horses evolved on the plains of North America some 45 to 55 million years ago. Starting out as beagle-sized, multi-toed creatures inhabiting a damp, primeval world, they changed along with their environment until they became the fleet, long-necked, single-toed animals we know today. By contrast, Homo sapiens sapiens, today’s human beings, are relative Johnny Come Latelies, having emerged from the evolutionary record only about 50,000 years ago.
Around 9,000 BC, horses spread from North America to Asia, Europe, and finally to Africa. Not long after this, the land bridge across the Bering Strait disappeared under the melting ice pack, leaving the horses of North America isolated on a changing continent. Within a thousand years, they slipped into extinction along with the sloth and the mastadon, not to return until the Spanish brought them on ships in the early 16th century.
According to tradition, the first horses to return to the New World were the sixteen that Cortes unloaded at Vera Cruz in 1519, of which eight were said to be bay or sorrel, three gray, two brown, one black, and two piebald or paint. More breeding stock arrived soon after, and by 1541, the conquistador Francisco Vasquez de Coronado had little trouble rounding up fifteen hundred horses for his expedition to what would later be New Mexico and Kansas.
The spread of horses across the plains proceeded rapidly. In 1719, the French explorer Du Tisne reported to his superiors in Louisiana that the Wichita Indians, who had never seen a horse before Coronado appeared among them in 1541, owned upwards of three hundred of the animals which “they esteem[ed] greatly” and with which they would not part for any price. A hundred years later, the American explorer Stephen H. Long put the number of horses owned by the Pawnee at somewhere between 6,000 and 8,000 head, or roughly four horses for every warrior in the tribe.