The process of evolution of modern horse from its ancestor Eohippus is elucidated in the given diagram.
Overall, it is clear the evolution focused on the development of foot structure, and it took forty million years.
The oldest ancestor of horse was termed as ‘Eohippus’, which was smaller in size, with four-toed foot. After 10 million years, it transformed into ‘Mesohippus’ which was slightly larger in size than its predecessor. A notable change occurred here was in the foot structure, where the number of toes in its foot reduced to three, with a prominent middle one. Fur was distributed on the back of its neck.
The second stage occurred 15 million years ago – ‘Merychippus’ – which was even larger in size and a more prominent middle toe. It also had thicker fur and longer tail.
The modern horse, the largest in its lineage, has a complex foot structure. The toes gave way to a hoof, which balances its body mass .Thick coat of long fur on the back of its neck and hairy tail make it very distinct from its predecessors.
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