Backbones of ocean-dwelling mammals evolved differently than those of species living closer to shore, study finds

If you’ve ever seen dolphins swim, you may have wondered why they undulate instead of moving side to side as fish do. Though they have a fishlike body, cetaceans, which include whales, dolphins, and porpoises, are mammals that descended from land-dwelling ancestors.

Cetaceans have undergone profound changes in their skeletal structures to thrive in aquatic environments, including the reduction of hindlimbs and the evolution of flippers and tail flukes, resulting in a streamlined body. Scientists still don’t understand how the transition from land to water, approximately 53 million years ago, impacted cetaceans’ backbone, a central element of their skeleton.