Our jawbones evolved into ear bones

Mammals are unique in having three ear bones, which allow for finer detection of sound. It turns out that these bones of your middle ear were once part of a mammalian ancestor’s jaw. Now a remarkable Cretaceous fossil provides a snapshot of how this shift took place.

The lower jaws of modern mammals have just one bone: the tooth-bearing dentary. Reptiles, by contrast, also sport smaller bones where the jaw meets the skull. Biologists have long hypothesised that as mammals evolved, the smaller, post-dentary jaw bones shrank to form the tiny bones of the middle ear.

Fossils of ancient mammals such as Morganucodon hint at this: the post-dentary bones are still attached to the dentary, and are used for both hearing and feeding. What happened next had been left to best guesses.

Now Liaoconodon hui has filled the gap. It is the first unambiguous evidence showing that transitional stage of the evolution of our ear bones. Read more here or here.

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