The picture illustrates the evolution of quine species through 40 million years, with particular emphasis on its foot structure

The picture illustrates the evolution of quine species through 40 million years, with particular emphasis on its foot structure. Overall, ancestral species and modern horse have the common trait of being quadrupedal, plus the animal has a more prominent dimension and thicker hair over the period shown. Its toes disappear little by little, eventually substituted by a sole hoof. The first ancestor was Eohippus, which existed 40 million years ago. Its torso was more miniature with four short limbs and hardly observable tail. It still had four separated digits with thin phalanges. Mesohippus and Merychippus were the two ensuing descendants, which survived 30 and 15 million years ago subsequently. The overall morphology was almost stable from Mesohippus to Merychippus. They both have a slight improvement in outward aspects along with elongated tails and a rudimentary form of the mane. Furthermore, the number of toes reduce to three, and the middle phalanx is enlarged. Finally, the horse that subsists these days is the largest size animal whose height and length are about three halves of its oldest shown ancestor. Its tail and mane appear pronouncedly. Additionally, the modern horse’s foot has the fewest bony structures that the hoof has fully replaced phalanges.