Hippos Are the Closest Living Relatives of Whales

Hippos are the closest living relatives of whales, sharing a common ancestor roughly 50 million years ago.

Biology

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Whales and hippos look almost nothing alike, but evolutionary evidence places them surprisingly close on the mammal family tree. Modern genetic and anatomical studies identify hippos as the closest living relatives of cetaceans, the group that includes whales, dolphins, and porpoises. Their shared lineage goes back tens of millions of years, with estimates placing their divergence roughly in the 50 to 55 million year range. This does not mean that whales evolved directly from hippos, or that their common ancestor looked like either animal. Instead, both groups descended from an older ancestor and then followed very different evolutionary paths. Whales eventually became fully aquatic marine mammals, while hippos remained semiaquatic land mammals. Scientists have used both DNA and anatomical features to reconstruct this relationship, including distinctive structures in the skull and other shared traits. The relationship is also reflected in the name Whippomorpha, a group that contains both hippos and cetaceans. Fossils help fill in parts of the story, although the early history of the hippo lineage has significant gaps in the fossil record. The result is one of evolution's more surprising family connections: the enormous animals that live in the ocean and the heavy mammals that spend much of their time in rivers and lakes are distant branches of the same ancient family.

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