The diagram illustrates the development of prehistoric and modern horses over the span of 40 million years with special emphasis on the formation of the feet.
From an overall perspective, it is very apparent that as the horses became larger in size, their feet underwent morphological changes, particularly in their size and structure. Their legs elongated and broadened, showcasing a change from four phalanges to a fused hoof.
Beginning from the prehistortic horse that lived approximately 40 million years ago named Eohippus, their body is distionguahable by it’s petite size and a feet containing four phalanges. Over the next 10 million years, Eohippus evolved into Mesohippus. These horses exhibited a larger body with a longer neck and longer legs, resembling the current day horses. In addition, their feet developed into three digits with the middle one being bulkier and slightly longer.
Living around 15 million years ago, Merychippus marks another evolution towards modern-day horses, their foot structure evolved to emphasize the central digit, which became enlarged and elongated. They also developed longer legs. This leads directly to the modern day evolution of horse which is largest in size, a full mane, and a single hoof which is a result of the fused digit.
In conclusion, the horses in the current period is in the fourth stage of the evolution where the notable development over the span of 40 million years is the increase in body size and the changing in the size and structure of the feet.