Here's a simplified timeline of horse evolution:
* 55 million years ago (mya): Eohippus - about the size of a fox, with four toes on its front feet and three on its hind feet. It was a forest-dwelling browser, grazing on soft leaves.
* 40-30 mya: Mesohippus - larger than Eohippus, with three toes on each foot and a slightly longer neck. It was more adapted to grasslands.
* 25-5 mya: Merychippus - even larger, with one large toe (the middle one) on each foot that eventually evolved into the hoof. It was a fast runner and adapted to open grasslands.
* 5 mya-present: Equus - the modern horse, with a single toe on each foot, a long neck, and a long head with large eyes. It could run fast and long distances, making it well-suited for open grasslands and hunting.
Where did they spread?
Horses originated in North America, but then migrated to other continents. During the Pleistocene epoch (2.6 million to 11,700 years ago), horses were found throughout much of the world, including Europe, Asia, Africa, and South America. However, they went extinct in North America around 10,000 years ago.
Modern horses were reintroduced to North America by European colonists in the 15th century.
It's important to remember that this is a simplified overview of horse evolution. The process was much more complex, with many different species evolving and going extinct over millions of years. However, the story of the horse's evolution is a fascinating example of how species adapt to their environment over time.