Low-frequency hearing limits are connected to longer cochleae and relatively larger cranial widths. Very LF hearing in Mysticeti appeared in the middle Miocene, and mysticete infrasonic hearing had evolved by the late Miocene.
Our results of the cochlear coiling shape analysis suggests that a shift of the frequency range towards the lower end, including the ability to hear very low and infrasonic frequencies, is associated with compact coiling, a non-gradual ascent of the basilar membrane, the basal end of the basilar membrane below the level of the basal turn, the second turn protruding over the basal turn, a descending apex, and a high number of turns (2.2 or above). Furthermore, low lf hearing limits occur in cetaceans with longer cochleae.
Very low-frequency hearing (50 Hz and below) had likely evolved by the middle Miocene, and infrasonic hearing (below 20 Hz) had evolved by the late Miocene. Even the earliest Chaeomysticeti were probably able to hear frequencies of 100 Hz and below, and the ability to hear low frequencies within the audible range may be ancestral to all Neoceti.
Cochlear coiling shape proved useful for inferring hearing range, as did number of turns and cochlear length times number of turns. Radii ratio is not directly connected to lf hearing in our study, and, to date, the method has not been used in a standardized, comparable manner.
Partners
Helmholtz-Zentrum für Materialien und Energie Berlin
Bundesanstalt für Materialforschung und -prüfung Berlin
Duration
20.02.2013 – 31.10.2016
Funding