All whales and dolphins are descended from terrestrial mammals, ancient creatures that were very similar to the modern hippopotamus. Now, a fascinating new genetics study shows the incredible evolutionary changes these animals had to experience to become the perfectly adapted marine animals we see today.
Biologists aren't entirely sure which creature modern cetaceans (dolphins, whales, and porpoises) are descended from. The traditional theory suggests mesonychids, an extinct order of carnivorous ungulates (hoofed animals) which resembled wolves. But more recent genetic analysis points to artiodactyls, a hippo-like creature. Regardless, all cetaceans were land mammals at one point in their evolutionary history — and they had to undergo some rather remarkable changes to adapt to underwater life.