The diagram depicts the evolution of the horse over a period of 40 million years, with a concentration on its foot structure.
Overall, The horse has significantly increased in size from its ancestor, Eohippus, to the contemporary horse. Another important feature is the progressive simplification of its toe structure.
Approximately 40 million years ago, Eohippus, which had a dog-like size, characterized by a short head and neck, developed five toes, four of which bore small hooves, while the fifth remained elevated. Dating back to 30 million years ago, Mesohippus emerged as an intermediary species, exhibiting a larger and more slender physique, and ambulating on 3 toes.
By 15 million years ago, Mesohippus had transformed into Merychippus, marking a significant milestone in equine evolution. While still retaining the primitive trait of three toes, Merychippus resembled a modern horse, featuring an elongated face, a newly-formed mane, and a larger body. Ultimately, the contemporary horse, derived from Merychippus, now possesses a single hoof, slim legs, an elongated head, a relatively extended neck, and a lengthy tail.
