A review of some current concepts of the functional evolution of the ear in terrestrial vertebrates

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Abstract

In the middle ear, the main selective pressure which favored the introduction of the lever ratio between ossicles in the Mesozoic reptiles ancestral to mammals was an improvement in sensitivity over the type of middle ear then extant. Modern columella systems, for example in birds, have independently evolved to be as sensitive. An improvement noted in high frequency transmission in modern mammal middle ears is unlikely to have been a selective pressure in Mesozoic reptiles. In the inner ear, selective pressure favoured the development and maintenance of higher endocochlear potentials for greater sensitivity at the hair cell level. With regard to the basilar membrane, elongation from the elliptical condition brought about consistent frequency analysis, and further elongation extended the range of frequencies the membrane could analyze. Physical restrictions have limited this elongation in some birds, but coiling in the mammals has permitted elongation which in some cases allows analysis of very high ultrasonic frequencies.

Original languageEnglish
Pages (from-to)608-621
Number of pages14
JournalEvolution
Volume26
Issue number4
DOIs
StatePublished - 1972
Externally publishedYes

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