Investigation into the possible role of dolphins' teeth in sound reception

Odontocetes use active sonar for echolocation, navigation and socialisation. This sonar is characterised by narrow transmission and reception directivity patterns, over a variety of ranges. There is physiological and behaviouralevidence to suggest that dolphins hear the echoes of their high-frequency clicks through their lower jaws. Current theory suggests that sound is transmitted through a thin region at the base of the jaw into a waveguide leading to the ear. The angular precision predicted by this theory is however much less than dolphins have been observed behaviourally to be able to do. A novel hypothesis is that the teeth of the dolphin's lower jaw act as an end-fire sonar array. This paper will start by putting these competing hypotheses into their context, presenting bioacoustics in the ocean, dolphin echolocation physiology and acoustic behaviour, and presenting the mechanical properties of bones and teeth. This information is used to model the reception of different sounds by bottlenose dolphins (Tursiops truncatus) with each possible mechanism, investigating the variations with nerve delay, the role of the jaw relative to the teeth, and the resulting changes in frequency sensitivity and directivity. The results can then be compared with observations of behavioural patterns.