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Equine Toes

When a horse lifts its hoof up and scrapes at the ground, repeatedly, something is off. Something is bothering the animal. In pawing the ground, the horse expresses its frustration.

But is it also giving us the middle finger?

Technically, yes. That’s what the hoof is, studies over the past several years confirm: a giant middle finger.

Reach back far enough into time and you will find a horse with five toes. Fifty-five million years ago, many of the horses in the warm, subtropical forest that made up North America were three- or four-toed. Then, climatic change brought about evolutionary change.

Thirty-five million years ago, as global temperatures fell, so too did the forests. Horses found themselves grazing on dry grasslands. Three or four toes, it turns out, weren’t so useful in such an environment. "Hooves and long legs helped horses run farther and faster on the open prairie, helping them flee predators and find fresh grass for grazing,” according to the American Museum of Natural History. By nine million years ago, three-toed equines were phased out of the evolutionary equation, giving way to horses with a single hoof.

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So where did the digits go? Did they vanish into thin air, consigned to the trash bin of evolution?

Not quite, according to a 2020 study featured in the New York Times.

Dr. Katharyn Kavanaugh, a biologist at University of Massachusetts, Dartmouth, was studying preserved horse embryos when she came across a discovery of sorts. In the part of the embryo where the hoof forms, she counted clusters of developing cells, representing toes. And she did not find just one or two —she found five.

One would think, after millions of years of inactivity, all evidence of previous horsey digits would disappear. But, for a short period of time in the gestational period, at a microscopic level, all five digits live on.

The finding suggests that a horse embryo, in “growing from a tiny wad of cells into multiple specialized tissues,” follows a certain ancient programming when it comes to its anatomy. And that programming requires the formation of those five clusters, even though they don’t develop into five adult equine toes.

Dr. Kavanaugh’s findings follow a 2018 study in which lead author Nikos Solounias dissected fetal and adult horses and found a surprisingly complex neurovascular network. Said Solounias, "If there are five fingers, there should be 10 primary nerves and 10 arteries—exactly what we found.”

So, when working on the ANATOMY IN CLAY® LEARNING SYSTEM’S EQUIKEN® model, perhaps it is important to think of the five ancestral equine digits as not having disappeared, but instead having taken on a new life, a different form.





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