The development of the horse over a period of 40 million years is described on the given diagram.
Overall, the figure places a main focus on the foot structure which changed over time as well as the extension in body size. It appears that the creature’s foot become larger in size.
Firstly, the evolution starts with the Eohippus, which existed 40 million years ago. Its foot structure consisted of four toe bones, which were rather slim. With 10 million years of change, two middle toes seem to merge to become a larger one, which reduces the total toe count to three. The new creature was called Mesohippus at this stage.
Secondly, with another 15 million years of evolution, the bone shape became more thicker and stronger. Also, the name of Merychippus could be used at this period. In addition, a development occurred with the toes as they evolved both in size and length, especially the middle one.
Lastly, when looking at the modern horse, it is evident that all previously mentioned toes are gathered into one structure and the total length and thickness of the foot is greatly impro
