Hearing of whales and dolphins
The auditory system of cetaceans - toothed whales, dolphins, and porpoises - features (i) deep modifi cation of sound-conductive structures adjusted to aquatic media of high acoustic impedance and (ii) a number of unique abilities. This system functions within a frequency range wider than 100-150 kHz (contrary to a few tens kHz in majority of terrestrial mammals, in particular 16-20 kHz in humans). It features sensitivity of 10-13-10-14 W/m2 (contrary 10-12 W/m2 in humans). The temporal resolution of the system is characterized by the integration time of about 0.3 ms, which in frequency domain corresponds to the cut-off frequency of 1700 Hz (contrary to 7-10 ms and 50-70 Hz, respectively, in humans). The frequency tuning is characterized by equivalent rectangular quality of 30 to 50 (contrary to 9-10 in humans). The directional selectivity is characterized by the receiving beam width of  6-11 and interaural intensity difference-vs-azimuth rate of about 2 dB/deg, which may be a basis of spatial resolution of 0.5. Discovering of these abilities of the auditory system contributes to knowledge of some basic mechanisms of hearing, in particular, the frequency range available for active frequency-tuning cochlear mechanism, the role of spatial and temporal coding for acute frequency tuning, the factors limiting hearing abilities of majority of terrestrial mammals and humans.