The diagram illustrates the evolution of the horse , with particular emphasis on the foot structure changing progress
Overall, the body structure of the horse has witnessed a lot of change, principaly the growth in size and reduction of toes number. In addition, the horse possessed different name in other eras.
At 40 million years ago, the horse at that era – which is called Eohippus – possessed a simlar appearance with the donkey except their ear was smaller. They did not have mane, and their foot had 4 toes that indistinctive to that of monkey. Going through 10 million years of evolving, the horse at 30 million years before show a noticable increase in size and shape. Compare to Eohippus, the Mesohippus – the horse of 30 million years ago – was 1.5 times larger, their leg and neck had been lengthen and the mane start to grow along side the neck bones. The most significant change was the feet, there were 3 toes in each foot, the middle toes was the biggest.
The Mesohippus continue to evolved and became Merychippus at 15 million years before. The Merychippus shared a same body structure with the Mesohippus. The mane of them was longer and their back was no long humpbacked. The foots bone structure have a few change in the size of toes bone, while the middle one keep growing larger, the two side toes were minimized. Finally, the Merychippus had reached their completed form – which is the horse we seen nowadays. The horse have longer leg, wider neck and breast, the mane and tail of them are also more hairy. The most crucial shift occur at the feet bone of them: their is only 1 toes now, in other words, the toes have merged into 1 and become the foot.