Baleen whale skulls are acoustic antennas

Mysticetes (baleen whales) produce and receive underwater sounds with wavelengths much longer than their bodies, despite having ears approximately the size of a human fist. How do they hear long wavelength sounds with relatively small ears? In 2015, Cranford and Krysl constructed a computational finite element model to simulate low-frequency hearing in a fin whale. That study predicted a hearing mechanism that involves bone conduction through the enormous skull. Physical, vibroacoustic experiments with gray whale skulls show that long wavelength incident underwater sounds excite the skull. These skull vibrations are transferred to each bony ear complex. The tympanoperiotic complexes contain dynamic components: flexible pedicles, dense tympanic bullae and middle ear ossicles. Anatomic geometry of the dynamic components mechanically amplifies the skull vibrations and delivers them to the cochlea through the stapes footplate. At the oval window, mechanical vibrations are transformed into hydrodynamic fluid displacements within the inner ear. These results validate the bone conduction hypothesis (Morris et al., 2025). Sound reception through the skull, with amplification in the bony ear complexes, is key to understanding mysticete low-frequency hearing. Bone conduction hearing is likely functional in all mysticetes due to commonalities of anatomic geometry and functional morphology.