The evolution of the horse
Horse belong to a family of animals 50 million years old. The earliest ancestor of the horse. called Hyracotherium, was a size of the dog, and had four-toed feet. Its descendants grew bigger, and evolved longer legs with fewer toes. Today's horses have just one toe or hoof on each foot.

From tadpole to frog
The ancestors of frog were fish that could pull themselve around using strong, fleshy front fins. About 300 million years ago, these fish gradually started to crawl out onto dry land. Today, frog still re-enact this part of their past, because they start life as todpoles, which swim around by lashing their tails. After a few weeks tadpoles start to lose their tails. They grow legs and take up life on land.