Historia Animalium 502a10
"The Egyptian hippopotamus has a mane like a horse, is cloven-hoofed like an ox, and is snub-nosed. It has a huckle-bone like the cloven-footed animals, tusks which just show through, the tail of a pig, the neigh of a horse, and the size of an ass. Its hide is so thick that spears are made from it. Its internal organs resemble those of the horse and the ass."