Catching evolution in the act

Many scientists have long suspected that the tiny bones in the middle ears of all modern-day mammals evolved from bones in ancient reptilian jaws, but direct evidence was lacking. Now, paleontologists have unearthed fossils that appear to show the transition.

Mammals have three delicate bones that transfer sound in their middle ears. Reptiles don’t have such a configuration but do have three bones that make up the rear edges of their lower jaws, says Zhe-Xi Luo, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh.