The Tympanal Recess of the Cetacean Cochlea: Function and Evolution

Cetaceans (whales and dolphins) primarily use sound to communicate and hunt for prey. Their auditory anatomy is highly specialised, but much about its function remains unknown. In particular, a feature of the cochlea known as the tympanal recess present in some mysticetes (baleen whales) and odontocetes (toothed whales) has defied functional explanation. Here, we present and discuss several hypotheses that may clarify the function and evolution of the tympanal recess. One potential function in particular, the vibroacoustic duct mechanism, seems most plausible although further work is needed to test the hypothesis, which hints at the possibility of sperm whales and beaked whales being able to detect both high and low frequencies.