From Land to Sea

Whales did not start in the water. They evolved from small, four-legged land mammals that waded back into the sea around 50 million years ago. Their closest living relatives are surprising: not seals or fish, but hippos. The largest creatures ever to live began as wolf-sized animals hunting in warm, shallow coastal waters.

Meet Pakicetus, one of the earliest whale ancestors. It still had four legs and spent much of its time on land near water. Over millions of years, its descendants reshaped their whole bodies: front legs became flippers, hind legs shrank away, the nostrils crept toward the top of the head, and a powerful tail fluke appeared. No single leap did this — the change came one small step at a time.