A Review of Some Current Concepts of the Functional Evolution of the Ear in Terrestrial Vertebrates

Comparative aspects of cochlear functional organization in mammals

“…Estimating hearing abilities from gross cochlear dimensions and shape is a fascinating approach that has been used for many years (Manley, 1971(Manley, , 1973 which can be applied to fossil ears and the ears of extant mammals that cannot be studied experimentally.…”

Vertebrate pressure-gradient receivers

“…As stated above, the most parsimonious assumption is that the coupled ear is the ancestral condition in all lineages that developed a tympanic ear (Christensen-Dalsgaard and Manley, 2005;Christensen-Dalsgaard and Carr, 2008;Köppl, 2009;Manley, 2010;Novacek, 1977). Thus, the middle ear enclosures in recent mammals and turtles are derived conditions.…”

“…Until the Triassic, before the emergence of the tympanic ears in the different groups, hearing in the tetrapods must have been based on mechanisms similar to bone conduction (Allin, 1975;Manley, 1973;Christensen-Dalsgaard and Carr, 2008). The early tetrapods would probably have been most sensitive at low frequencies.…”

“…On the other hand, the isolated tympanic ear had increased sensitivity at low frequencies, and taken together, this may have led to a transformation of the low-frequency pathway to a time pathway in birds and mammals. Conversely, the loss of high-frequency directional information led to the emergence of external ears and other structures that could increase sound diffraction cues (Manley, 2010). Additionally, the increase in high-frequency sensitivity in the mammals would further increase sound diffraction cues, but the binaural comparisons of these cues would still mainly be based on interaural level differences (Christensen-Dalsgaard and .…”

“…For example, acoustical connections through the cricket trachea generate a useful directionality at the frequency (5 kHz) of the cricket calls (Michelsen and Larsen, 2008), definitively a derived condition in crickets and their near relatives. In vertebrates, in contrast, we now assume that a coupled eardrum system is the ancestral condition of the tympanic ears (Christensen-Dalsgaard and Manley, 2005;Christensen-Dalsgaard and Carr, 2008;Köppl, 2009;Manley, 2010;Novacek, 1977) that originated independently in all the major vertebrate groups. This assumption follows from the observation that the early tympana covered spiracular openings into the mouth cavity (Clack, 1997).…”