Some of our bones are easy to see. The zygomatic bones that give our cheeks shape, the delicate phalanges of our fingers, and the bony bulbs that are our kneecaps all stand out from beneath the flesh.

The 165-million-year-old fossil of a tiny, shrew-like animal shows the earliest example of modern hyoid bones—the ones that provide the ability to swallow food—in mammal evolution. The hyoid bones of ...