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The prehistoric horse took thousands of years to lose its toes

Posted in Animals, Nature, Prehistory on Monday, 28 October 2013

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This edited article about animals originally appeared in Look and Learn issue number 442 published on 4 July 1970.

Orchippus and tiger, picture, image, illustration

Orchippus being pursued by a prehistoric tiger

The earliest known member of the horse family was Eohippus. It was about the size of a fox and much smaller than the domestic horse of today. But Eohippus starts the 50-million-year evolutionary journey of the horse.

Its successor was Orohippus. Orohippus was very much like Eohippus in appearance and had not yet developed much in size, being only 1 ft. 3 in. high at the shoulder. Its head was no longer than that of a dog and, although very early in its evolution towards the modern horse, had a remarkably equine appearance. The main difference in the appearance of Orohippus’s head was that its eyes lay further forward. As you know, the modern horse possesses hooves. These had not yet developed with Orohippus. It still possessed toes.

Some remains of this tiny forerunner of the horse were found in what is now known as the Bridger Basin in Wyoming. In the Eocene period, the time of Orohippus, the Bridger Basin was a swampy area with numerous lakes inhabited by crocodiles and turtles. Among the marshes and lakes were areas of grassy shrub-dotted plain. Orohippus selected these grassy plains for its home, unlike Eohippus, who had existed in the same region, but in the swampy areas.

Why did one early form of horse, Eohippus, change into another, Orohippus? The reason is that they changed to suit their environment. The most obvious changes came about in their teeth – changing from those suitable for chewing soft swamp plants to those suitable for chewing dry, tougher grasses found on the plains. Their feet also changed, from those suitable for slow, casual wanderings in the overgrown swampy areas to those suitable for the more speedy movement necessary to survive in the open plains.

Later, the grassy plains developed from small areas among lakes and swamps to wide, flat grassy plains, and the feet of the early horses changed with them, eventually becoming hooves, more suitable than ever for speed.

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