As Stephen Jay Gould once put it, we have an earful of jaw. The small, sound-conducting bones of our inner ears – the incus, malleus, and stapes – got their start as jaw bones in our distant ancestors, and the modification of bits of jaw into intricate ear components is one of the classic examples of major evolutionary transformation. This was brilliantly demonstrated in a paper simply called “The Evolution of the Mammalian Ear” by paleontologist David Meredith Seares Watson in 1953, but, as Watson himself recognized, his transitional series was only a general outline of the change based upon the fossils available at the time.

Thanks to a combination of fossil discoveries and investigations of embryonic development, the correspondence