The Modern Horse

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Modern horses belong to the species E. caballus within the genus Equus, the only extant genus of the family Equidae. Within the genus Equus, horses, asses, and zebras are the only surviving species.

The genus Equus evolved into its present form on the North American continent, as documented in continent’s fossil record. During a period of major glaciation during the Pliocene epoch (2.6 million years ago), some Equus species crossed from North America to the eastern hemisphere.

In Africa, they diversified into modern zebras; those who spread to Asia, the Middle East, and North Africa developed as desert-adapted asses, both domesticated and wild (onagers). True horses, E. caballus, spread through Asia, the Middle East and Europe.

In the western hemisphere, horses became extinct about 10,000 years ago, at a time in the late Pleistocene when a series of extinctions eradicated most of the large mammals, including not only all of the horses in North and South America, but also mammoths and saber-tooth tigers. A combination of climatic changes and overhunting by H. sapiens, a recent arrival in the hemisphere, is believed to have been responsible.

Extant species within the genus Equus are E. burchelli, the Plains zebra of Africa; E. zebra, the Mountain zebra of South Africa; E. grevyi, Grevy’s zebra; E. caballus, the true horse; E. hemionus, the desert-adapted onagers; and E. asinus, the true asses and donkeys of north Africa.

Horses were reintroduced into the western hemisphere by European explorers, conquerors, and settlers. Juan Ponce de Leon brought horses, as well as cattle and hogs, to the Gulf Coast of Florida in 1521. Nineteen years later, Francisco Coronado carried horses into the southwestern part of what is now the United States.

Native Americans in this area acquired horses from breeding stocks that developed from the horses that had originally been brought by the Spanish. But there were no horses in the eastern part of the continent north of Florida when the first settlers arrived at Roanoke(1584)and at Jamestown(1607).

The wild ponies of Assateague and Chincoteague may be descendants of survivors of a wrecked Spanish ship. Spanish fleets traveled to the new world carrying horses for the armies that conquered Mexico, Peru, and other parts of the Caribbean, Central, and South America; these fleets returned home by a route that took them along the coast of North America. While they would not have carried many horses on this part of their journey, some could have been aboard a ship that was wrecked.




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