Evolution of the cochlea and the elongated cochlea allows for better sensitivity for higher frequencies. As in all lepidosaurs and archosaurs, the single-ossicle (columellar) middle ear transmits sound to the footplate of the columella, which sends a pressure wave through the inner ear. In snakes, the basilar papilla is roughly 1mm long and only responds to frequencies below about 1 kHz. In contrast, lizards tend to have two areas of hair cells, one responding below and the other above 1 kHz. The upper frequency limit in most lizards is roughly 5–8 kHz. The longest lizard papillae are about 2mm long and contain 2000 hair
Evolution of the cochlea forces for the larger cochlear labyrinth may have started after the basal primate node. Mammals are the subject of a substantial amount of research not only because of the potential knowledge to be gained regarding humans, but also because of their rich and abundant representation in the fossil record. The spiral shape of the cochlea evolved later on in the evolutionary pathway of mammals than previously believed, just before the therians split into the two lineages marsupials and placentals, about 120 million years ago. Parallel to the evolution of the cochlea, prestins show an increased rate of evolution in therian