The North American horse is deeply entrenched in global society. The horse transformed the Western Plains, drove agriculture and influenced the North American transportation system. The prehistoric horse in North America evolved over a period of 50 million years. To date, scientists have pinpointed the original horse, Eohippus, which resembled a small dog. The horse has undergone multiple changes over the past 50 million years and today holds a place deep within the human heart.
The Eocene and Oligocene Eras
The modern-day horse, Equus, has undergone multiple changes throughout the stages of evolution. For example, the Eohippus--a dog-like horse that lived during the early Eocene era-- was very small and had three distinct toes. This animal evolved into Orohippus and scientists do not consider it a true horse. It had the same body size as Eohippus, but the toes were slightly different; it had four toes on each front leg and three toes on each hind leg.
Three-million years later, Epihippus evolved from Orohippus. Scientists note that during the early evolutionary period, horses developed teeth fit for grinding. Epihippus was no exception. In fact, these animals began to exhibit some traits common to modern-day horses. For example, Epihippus possibly spent more time grazing on flatter lands and had grown stronger teeth to grind vegetation. Epihippus gave way to the next generation of early horses, Mesohippus, roughly 38 million years ago.
The Miocene and Pliocene Eras
Scientists call the Miocene and Pliocene eras the time of the true equine. Kalobatippus lived in the forests. This animal had four front toes of which the second and fourth evolved to navigate the forest floor. One of the most successful early horse species was Merychippus. This animal lived during the Miocene era and scientists believe it is the ancestor of at least 19 more species living in grasslands.
Merychippus ' success led to several descendants including Hipparion and Pliohippus. Hipparion was a successful breed that existed for roughly 22 million years going extinct 781,000 years ago. This animal lived on the grassy plains and prairies similar to modern day horses. Despite this, Hipparion was still relatively small with several specimens weighing in at less than 300 pounds. Pliohippus also evolved, and many believed it was closely related to modern day horses, although science says it is more closely related to Equus.
Scientists have found the oldest evidence of modern-day North American horses in Idaho. The remains found belong to Equus simplicidens and are roughly 3.5 million years old. Paleontologists believe that Dinohippus, or terrible horse, is the ancestor of Equus. While the animal had a fearsome name, it only weighed about 750 pounds and reached a height of 5 feet. One of the Dinohippus' characteristics that link it almost directly to Equus is its ability to stand for extended periods. Dinohippus was a larger animal and fossil evidence was found across North America, including Canada and Florida. This animal also developed one hoof.
Today's Equus genus contains donkeys, zebras and horses. This species evolved during the Pliocene era in North America. The animal's success is evidenced in its wide distribution. Paleontologists believe that Equus migrated to Eurasia. The ice age contributed to the extinction of horses in both Americas. The Equus species survived in its migratory lands and Europeans reintroduced the species to North America during the 15th and 16th centuries.
Over the next 500 years, from the 14th century to the 20th century, the horse would have an astounding effect on North American agriculture, transportation and industry. Columbus bought the first Spanish horses to the Americas during the late 15th century. Columbus bred these animals so the conquistadors had transportation when they went out on expeditions. Today, the wild horses that live along the Shackleford Banks in North Carolina are proven descendants of Spanish horses from 400 years ago. Recently completed genetic testing indicates their heritage. The North American horse has undergone multiple changes since prehistory. The horse's evolution began 50 million years ago with a small, dog-like creature. Today, the horse weighs up to 1500 pounds, supports North American farming and participates in important events around the world.
Review the following resources for more on prehistoric horses of North America:
Written by Sharon Rogers