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Ancient Animal Is Ancestor to Whales and Hippos, Scientists Say

January 2005

Despite differences of appearance and habitat, hippos and whales are first cousins.

An international team of scientists has proposed they share a common water-loving terrestrial ancestor, which lived 50 to 60 million years ago and evolved into two groups: early cetaceans, which became completely aquatic, and a large group of pig-like terrestrial animals called anthracotheres, whose only surviving descendent is the hippopotamus. Its paper appears in the journal Proceedings of the National Academy of Sciences.

Countering the assumption that hippos and pigs are cousins—which was based largely on similarities between their molars—molecular studies in recent years indicated that hippos have more in common with cetaceans (whales, porpoises, and dolphins). This recent study of hippo, whale, and anthracothere fossils supported the molecular evidence and led to the conclusion that whales belong to the group of even-toed ungulates known as Artiodactyla, which includes sheep, antelopes, giraffes, and most other large land mammals.

Today's hippopotamuses spend their days in or near rivers, lakes and wetlands of sub-Saharan Africa, grazing nearby grasslands at night. Whales can be found in oceans around the planet, and, depending on the species, feed on everything from other whales to plankton. Blue whales are the largest animals ever to have existed.

The family tree of modern whales and their first cousin, the hippopotamus, showing how the now-extinct anthracotheres are the link between their distant ancestors. Credit: Jean-Renaud Boisserie/UC Berkeley

Sources: Reuters, BBC News, University of California, Berkeley