Hippos were thought to be related to pigs until recent DNA analysis suggested that they're more closely allied to cetaceans than to other artiodactyls. Their common ancestor is thought to have split from other even-toed ungulates about 60 million years ago, with the two groups diverging about five million years later. The peculiar artiodactyl fossil Indohyus, from Eocene India, is placed by some within the hippo/whale clade. The earliest known hippo fossils (Kenyapotamus) date to around 16 million years ago, and are from east Africa. Hippos can hear well underwater, although they lack the thickened auditory bullae typical of whales.
mammals, hippopotamuses, cetaceans, paleontology, DNA