Like hippos, their closest living relatives, whales are descended from an ancestor that had four legs and walked on land, a transition explored in the upcoming exhibition Whales: Giants of the Deep, opening March 23.
Paleontologists have found fossil evidence of various “walking whales,” semiaquatic whales that show some early stages of the transition from land-dwelling ancestors to today’s familiar fully marine whales.
One such “walking whale” is Ambulocetus (am-bew-lo-SEAT-us) natans, which lived about 49 million years ago in what is now northern Pakistan, in long-lost coastal shallow seas and brackish rivers.
Although Ambulocetus was large—about 11 to 12 feet long—and had strong limbs, the animal probably could not walk well on land. After all, it had squat legs that splayed from its body, flipperlike hind feet, and it weighed about 400 pounds (180 kilograms).
On land it probably waddled and pulled its body with its forelimbs, a bit like sea lions do. In the water, Ambulocetus swam like a sea otter using its gigantic, probably webbed, hind feet.
Ambulocetus obviously had legs, and, though it may not seem like it, all modern whales do, too. The front legs of whales have evolved into flippers. And tiny, invisible-from-the-outside remnants of hind legs—mostly the hips—remain in the skeleton of some whales, inherited from their land-dwelling ancestors.
Learn more about the evolution of these marine mammals in Whales: Giants of the Deep, which opens at the Museum Saturday, March 23.