Hippopotamus

The hippopotamus (Hippopotamus amphibius) is a massive semi-aquatic mammal of sub-Saharan Africa that spends the day in water and grazes on land at night. It is listed as Vulnerable. Its closest living relatives are the whales, not the pigs it resembles.

🧬 Field Guide Specimen: Open Hippopotamus in the CRV Science Field Guide to log the specimen, see its place among the Mammals lineages in the Cladogram Explorer, and test your recall in the Red List conservation game.

DNA evidence places hippos and cetaceans together in a clade within the even-toed ungulates. Fossils support the connection, including the ankle bones of early whales like Pakicetus, which show the double-pulley shape typical of even-toed ungulates. Hippos and whales share an ancestor that lived roughly 55 million years ago.

Hippos cannot swim in the usual sense: they walk or bound along riverbeds. Their skin secretes a reddish fluid containing pigments that act as a sunscreen and antimicrobial. At night they travel several kilometers to graze, consuming several tens of kilograms of grass.

Hippo dung fertilizes rivers and provides food for fish, but in large concentrations it can also deplete oxygen. Poaching for meat and ivory-like teeth and habitat loss have reduced numbers to roughly 115,000 to 130,000 animals. A separate species, the pygmy hippo, is Endangered.

• Blue Whale — a cetacean relative
• Ecosystem — nutrient transfer between land and water