Evolution of the cochlea Evolution of the cochlea Cochlea is Latin for “snail, shell or screw” and originates from the Greek word κοχλίας "kohlias". The modern definition, the auditory portion of the inner ear, originated in the late 17th century. Within the mammalian cochlea exists the organ of Corti, which contains hair cells that are responsible for translating the vibrations it receives from surrounding fluid-filled ducts into electrical impulses that are sent to the brain to process sound. This spiral-shaped cochlea is estimated to have originated during the early Cretaceous Period, around 120 million years ago. Further, the auditory innervation of the spiral-shaped cochlea
Evolution of the cochlea cells and their afferent innervating fibers can be very sharply tuned to frequency. In birds and crocodilians, the similarity of the structure of the basilar papilla betrays their close evolutionary relationship. The basilar papilla is up to about 10mm long and contains up to 16500 hair cells. While most birds have an upper hearing limit of only about 6 kHz, the barn owl can hear up to 12 kHz and thus close to the human upper limit. Egg-laying mammals, the monotremes (spiny anteater and platypus), do not have a spiral cochlea, but one shaped more like a banana, up to