The middle ear of tetrapods (limbed vertebrates) originated from nonauditory structures, and has been modified by adaptations arising from the lifestyle of the tetrapods. These accessory structures for the inner ear increased the sensitivity to airborne sound, the frequency range of hearing, and the directionality of the ear. The tympanic middle ear originated independently at least once in every major tetrapod group and a long time after the origin of the tetrapods. The aim of the chapter is to give an outline of middle ear function and, a comparative overview of tetrapod middle ears and to describe how the middle ear has undergone diverse, major modifications (e.g., in aquatic, fossorial, or ultrasound-sensitive species). In some cases, these modifications even led to a reduction or complete loss of function of the middle ear, leading to decreased auditory sensitivity. These reductions were the result of unrelated, obviously more important, selection pressures.
Springer Handbook of Auditory Research: Springer Handbook of Auditory Research, 2014, p. 157-191