Description: The hippopotamus (Hippopotamus amphibius) or hippo, from the ancient Greek for "river horse", is a large, mostly plant-eating mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae (the other is the Pygmy Hippopotamus). The hippopotamus is the heaviest extant artiodactyl, despite being considerably shorter than the giraffe.