The diagram illustrates the process of horse evolution, with a specific changing on foot structure.
Overall, it is clear that while the structure of the body increased in evolution, the bone structure was also bigger and bigger in the period of time. However, the number of flangits showed a decreased structure at the same period.
From a detailed analysis, there had been a species called eohippus about 40 million years ago. Their foot structure consisted of four toe bones, which were thin and the body was smaller than a modern horse. Over ten years later, Mesohippis evolved with a similar body structure which has a larger body and the three distinct digits, the middle one being bigger and slightly longer.
In terms of 15 million years ago, the body shape became thicker and increased in size of the middle one, which is called Merychippus. When looking at the modern horse, all toes are gathered into one structure, as a hoof. It has a full mane and is the largest in size in the time line.