The diagrams illustrate the evolutionary changes horses underwent over a 40-million-year period, focusing on alterations in body size and foot structure.
Evidently, significant transformations occurred in both the overall size of the animal and the anatomy of its feet. Forty million years ago, the Eohippus, the ancestor of the modern horse, was considerably different. It was a small creature, characterized by a short tail and the absence of a mane. Over the subsequent 10 million years, the species evolved into the Mesohippus, which was notably larger, possessed a longer tail, and developed a mane. For the next 15 million years, the body size remained relatively constant, but the tail and mane became more extended. Furthermore, the foot structure began to change, with the development of joints in the legs and the initial appearance of a hoof. In contrast, modern horses are substantially larger than their predecessors, with long, flowing manes and tails. The leg muscles and overall anatomy are more developed, and the most striking difference is the fully formed hoof.
The foot structure of Eohippus, which existed 40 million years ago, comprised four toes of roughly equal size. Ten million years later, Mesohippus exhibited a reduction to three main toes, with the central toe being noticeably larger than the others. Fifteen million years ago, the Merychippus’s foot demonstrated further evolution with additional joints and the emergence of a rudimentary hoof tip, and a more prominent central hoof. Contemporary horses possess a single, large hoof, a consequence of the upper limb bones receding to enhance speed and endurance, while the hooves themselves have become significantly stronger.