The diagrams present the evolutionary development of the horse over a 40-million-year span, highlighting significant transformations in body size, hair features, and foot structure.
Overall, the horse evolved from a small, multi-toed animal into a much larger, single-hoofed mammal. This process was marked by a progressive increase in stature, the emergence of a mane, and the consolidation of the foot into a single hoof.
Chronologically, the Eohippus (40 million years ago) was a small creature with a short tail and no mane. Its foot structure was distinct, featuring four functional toes. By the Mesohippus stage (30 million years ago), the animal had grown larger and developed a visible mane and longer tail. The foot transitioned to a three-toed structure, where the central digit became more prominent.
Further evolution is seen in the Merychippus (15 million years ago), which maintained a similar body size to its predecessor but showed more defined leg joints. Its foot further specialized, with the side toes shrinking and the central toe beginning to resemble a hoof. Finally, the modern horse is significantly taller with a robust build, a long flowing mane, and a large tail. Crucially, the multiple toes have been entirely replaced by a single, solid hoof, and the leg bones have become longer and thicker.