One bone became particularly useful as a hearing device, the hyomandibular bone, a strut that, in fish, controls the gills and gill flaps.
In the first land vertebrates, the bone jutted downward, toward the ground, and ran upward deep into the head, connecting to the bony capsule around the ear.
Over time, freed from its role as a regulator of gills, the hyomandibula took on a new role as a conduit for sound, evolving into the stapes, the middle ear bone now found in all land vertebrates (save for a few frogs that secondarily lost the stapes).
At first, the stapes was a stout shaft, both conveying groundborne vibrations to the ear and strengthening the skull.
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Later, it connected to the newly evolved eardrum and became a slender rod. We now hear, in part, with the help of a repurposed fish gill bone.
When I lifted the violin to my neck and felt its touch on my jawbone, my mind filled with imaginings of ancient vertebrates. These ancestors heard through their lower jaws as vibrations flowed from the ground, to jaw and gill bones, to the inner ear. The violin drew me into a reenactment of this pivotal moment in the evolution of hearing, without the indignity of prostrating myself. High art meets deep time? Not in my incapable hands, but certainly in the artistry of accomplished musicians.
