The diagram presents information on how the horse evolved over a span of 40 million years.
Overall, the early Eohippus species went through four stages of development with significant changes in their foot structure and body size, eventually transferring into the modern horse we know today.
Around 40 million years ago, although the primitive Eohippus displayed typical horse characteristics such as a tail, a long neck, and four legs; its feet were different, with straight feet and four elongated toes. Over the next 10 million years, this species referred to as the Mesohippus chracterized a reduced number of toes to three, the larger middle toes among the two remaining, and a sparse mane along the top of its neck. These features were similar to the Merychuppus, which appeared in 15 million years subsequently. Finally, the modern-day horse fused to become a hoof and the leg joint was angled.
Regarding the body dimension, the Eohippus was much smaller, about half the height and length of the present-day horse. Over time, the body size gradually increased in the Mesohippus and Merychuppus, eventually reaching the size of today’s horse.