With a length of up to 4 m (13 ft) and weight of up to 3.5 tons, the Hippopotamus is the largest semi-aquatic animal and the third largest type of land mammal. Despite their physical resemblance to pigs, the closest living relatives of the Hippos are actually the cetaceans from which they diverged about 55 million years ago. The hippo lives in 29 African countries.