The horse evolves in America

The horse is one of the few animals whose entire evolution we can follow through fossils, from a forest creature the size of a fox to the animal we know. Almost all of that happened in North America. And it ends with the horse dying out on the continent that made it, and returning only aboard Spanish ships.

What actually happened

Around 55 million years ago a small animal lived in the forests of what is now Wyoming. It had four toes in front and three behind, teeth suited to soft leaves, and a back arched like a dog's. It is the oldest known member of the horse family.

What shaped its descendants was grass. As the climate dried and forests gave way to open plains, everything changed: grass grinds teeth down, so teeth grew taller and folded with enamel; open country offers nowhere to hide, so legs lengthened and toes reduced until only the middle one remained, reinforced into a hoof.

Timeline

55 million years ago

Eohippus in the forests of Wyoming, fox-sized, with toes

34 million

the climate cools and dries; forest gives way to open country

20 million

grasslands spread; high-crowned teeth and longer legs

5 million

Equus, the genus of every living horse, arises in North America

3 million

horses cross to Asia over Beringia, and on to Europe and Africa

11,000 years ago

the horse dies out across the Americas

1493

Columbus brings horses on his second voyage

1680

the Pueblo Revolt releases Spanish horses northward in thousands

1750

the Comanche, Lakota and Cheyenne have become horse peoples

Bushy, not a straight line

The usual textbook figure shows five horses in a row, each a little larger than the last. It misleads. The family tree is bushy: at its peak a dozen horse genera lived in North America at once, some with three toes and some with one, some grazers and some browsers. Most branches ended blind. That we can draw a straight line is because we know the answer and pick out the links that lead to it.

The loop

Horses crossed Beringia into Asia, and spread from there. Then, around eleven thousand years ago, they vanished from the Americas along with mammoths, mastodons and giant ground sloths. The cause is the same unresolved argument between hunting and climate that applies to the rest of the megafauna.

So when Columbus brought horses on his second voyage in 1493, it was a return, not an introduction. The animal came home to a continent it had been absent from for eleven thousand years.

What it did to the Plains

Spanish horses spread north from New Mexico, sharply accelerated by the Pueblo Revolt of 1680, when the Spanish fled and left their herds behind. By the middle of the eighteenth century the peoples of the Plains had built an entirely new way of living around the animal: Comanche, Lakota, Cheyenne, Blackfoot.

The order is worth holding on to. The mounted bison hunter is not a picture of an ancient America — it is younger than Bach's music, and it was made possible by an animal that arose in Wyoming returning there in the hold of a European ship.