Every Day Is Special: December 13, 2012

December 13, 2012 - Day of the Horse

If you are lucky enough to own a horse, today would be a great day to go on a nice long trail ride...OR to give your horse a day off and a special treat like peanut butter on toast, bananas, or grapes.

Most of us don't have horses, of course. But we can take a moment to think about the enormous contributions horses have made throughout history. Can you think of the Wild West or the plains Indians without horses? Medieval jousting tournaments and cavalries, rodeos and parades, wagon trains and stage coaches, farm horses and Clydesdales, circus horses and equestrian sports, Roman chariot races and the Pony Express—horses are a huge part of human history and an important part of modern life as well.

Horse evolution is often portrayed as a smooth line from Eocene (“dawn horse”) to modern day Equus, each stage larger and (I always think) more elegant than the one before.

The Equine "Family Bush"

But horse evolution has really been non-smooth and bushy, with lots of creatures branching off—including all the equids that still live today, including zebras and donkeys and a variety of wild asses and onagers. As in most family trees, most of the equine species that have ever lived are now extinct.

All these ancestors of modern
horses are now extinct.

One of the things I've always found interesting about horse evolution is that equids first evolved in North America many millions of years ago. Some species crossed over the “land bridge” that used to connect Alaska and Siberia around 2.6 million years ago and migrated throughout Asia and even into Africa and Europe. These equids diversified into various species of zebras and quaggas, asses and donkeys and onagers, and of course into the modern species we call “horse.” While all these equids were flourishing in the “Old World,” the North American equids died out! (Scientists' most recent evidence suggests that this extinction may have occurred around 7,600 years ago.) It wasn't until the late 15^th Century when the Spanish conquistadors arrived in America that horses were reintroduced to the North American continent.