Buried deep within the body of a whale, underneath the heaps of muscles and tendons, lie some little, lonely bones. They are whale hips–and they are one of the stranger examples of evolution’s transforming power. Perhaps kinkier is a better word.

Some 54 million years ago, the ancestors of whales and dolphins were four-legged mammals. Their anatomy was well-adapted for moving around on land, including their hips. Here, for example, is an ancient member of the whale lineage, called Indohyus. The hip bones of these early whale relatives had scoops where the balls of their femurs could be tucked away. They had shelves where leg muscles could anchor. While the hips themselves were made up of a cluster of bones,