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Przewalski’s Horse and other ancestors of today’s modern horse

No, this isn’t about my first horse, Mickey, which I borrowed for the summer before starting vet school.

The first time I got on that horse, my brothers were convinced they had witnessed my death. Mickey reared up and fell over backwards, with me riding bare back. Old Mickey fell on me — all 1,000 pounds of him — pounding my body into the ground, making a form so that a cast of my torso could be made. The imprint was so well defined, that if you had filled it with concrete you’d have a good start on a memorial statue of me, just in case my brothers were correct about my fate.

Mickey was old, at 25 years. But the story I have for you today will give you an idea of how old horses are as a species. Przewalski’s horse, named for Polish naturalist Colonel Nicholai Przewalski (ze-vahl-skee), is the only living remnant of three subspecies of equine that eventually became today’s modern horse.

The first equine ancestor was the size of a Jack Russell terrier. It had five toe pads, four of which were weight-bearing. Eventually, only three of the horse’s toes bore weight, and in more recent eons the third toe (cannon bone) carried all the animal’s weight.

The remnant toes became the chestnut, that horn like growth on the inside of each leg and the splint bones on each side of the cannon bone, incorporated into the suspensory ligaments of each leg. Scientifically, these bones in the front leg are classified as metacarpal bones and in the rear legs, metatarsal bones. Metacarpal bones are comparable to the bones in our hands. Metatarsal bones are comparable to the bones in the bottom of our feet.

The namesake of Przewalski’s horse explored much of Eurasia and first described this species during his forays into Mongolia in the 1700s. By this time, this intermediate horse ancestor weighed about 600 pounds, was dun colored (dark tan body with erect dark brown mane and tail) and lived in a social order that consisted of one stallion to a band of 10 or so mares.

Younger stallions foraged in bachelor groups until one would step out and challenge the leader of a band. Either the mature stud beat the upstart bachelor and drove the youngster away from his band or the young stud drove the old senior away.

Przewalski’s horse never was domesticated as a beast of burden. You’ll find Przewalski’s horses at zoos, as they survived the tests of time and poachers. In the 1960s, a major effort to breed them in captivity was started with the intent to return them to the steppes of Mongolia (China) and the Chernobyl region of Russia. Progress has been slow because poachers continue to decimate their numbers when the horses are released. Currently, about 300 range in the wild.

Thanks to genomic testing researchers now have a better understanding of the development of the prehistoric “horse” into today’s modern horse. The modern day horse was a result of three-way matches of interbreeding between Przewalski’s horses, Equis caballos and Equis complicates. Przewalski’s horse has 66 chromosomes rather than the 64 of modern horses. In spite of this, modern horses and Przewalski’s horses can breed, resulting in normal, fertile offspring.

In 2013, an equine bone, estimated at 550,000 to 760,000 years old, was found preserved in the permafrost of the Canadian Yukon territory. The bone contained preserved DNA, giving scientists further understanding of the ancestry of today’s horse.

The horse provided marauding Mongolian hordes a new means of attack. With the horse, they could swiftly move into a region, wiping out everything in their path. This revolutionary development was equivalent to our government’s use of drones in modern warfare.

Of course, horses — just like drones that are useful in other endeavors such as agriculture, weather forecasting and traffic control — have far greater uses than war. They found key roles in transportation and agricultural tillage.

And the speed that the Mongols valued is what has made horses good at delivering mail for the Pony Express and racing on tracks, like Secretariat. Speed is a genetic trait that appeared, amazingly, only in about the last 10,000 years by way of a genetic mutation.

Like me, you may never have owned a Black Beauty or Trigger, but just know there is a lot of history behind your horse’s genetic development, which traces back further than man himself.

Even old Mickey, that son-of-a-gun, had a rich ancestry.

 

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