How did the horses lose their fingers?

Horses can jump over large obstacles, gallop at speeds of up to 70 miles per hour and wear their own weight that can reach and tone – all with one finger on one leg.

Proceedings of the Royal Society B helps explain why fingers lost strength and speed of the horse

Together with zebra and ass, horses fall into just a few simple creatures in the animal kingdom. Scientists have thought for a long time to have a single-fingered foot – they allow horses to move faster and longer to the pastures, using them to flee the predators and find fresh food. But the hypothesis that it is better to have one big finger than a few smaller, biomechanically speaking, has never been directly examined.

"This study has taken an important step" in solving why horses lost their fingers during the early stages of their evolution, said Karen Sears, an evolutionary biologist at UCLA.

Horses in ancient times had many fingers to lose. Rod Hyracotherium, horses of the size of a dog that lived 55 million years ago, had four fingers on the front legs and three on the back. Horses from the genus Merychippus lived 10 million years ago and resembled a modern horse, but had three fingers, including a long fingers. Equus, evolving five million years ago

"If you look closer, you can see the shrinking bones of the bones that would grow to the fingers on the side of a modern horse," said Brian McHorse, Harvard paleontologist.

To monitor the evolution of horse feet, McHorse and colleagues used a CT scan of the internal structure of the fossilized bone bones of 12 different extinct horses. They were also analyzed by a pair of closely-related South American tapers, having similarly fingers like Hyracotherium. Computer simulation has allowed scientists to evaluate how the bones react to stress movements of any kind, such as skiping hurdles or accelerating from the pallet to the gallop. Then, scientists compared what happens when they apply full weight to the animal's body just to the center finger, and when it is distributed over several fingers.

Fingers on the side have significantly increased the ability of early horses to wear their own weight, revealed a team of scientists – the center finger of early horses would collapse without the help of other fingers. As the era of modern horses approaches, the lower fingers have fallen, but the middle finger bone has been strengthened and lost. These changes made one foot flat – almost equally strong and resistant to bending and compression such as a finger with multiple fingers.

As the legs of the horse grew, the additional fingers at the end of the limbs would be "like carrying weight around the articles," McHorse said. Rejection of these fingers helped save the energy in early horses, so they could travel longer and be faster, she said. The study can not determine which changes came first – did the strengthening of the middle finger affect finger fingers on the side or the loss of these fingers caused changes in the middle ear

Horses are not the only animals that have lost their fingers in evolutionary changes. "The fingers have lost many animals walking, running, jumping and flying," said Kim Cooper, a biologist at the University of California at San Diego. Modeling the influence of the force of motion on animal bones – living or extinct – could help scientists to understand why.

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