The effect of acoustic shielding of the region of a dolphin's mental foramina on its hearing sensitivity

The effect of acoustic shielding of the mental foramina of a bottlenose dolphin (Tursiops truncatus) on its auditory thresholds has been experimentally studied using the method of instrumental conditioned reflexes with food reinforcement. The detection thresholds of short broadband acoustic pulses deteriorated significantly (by 30-50 dB) under conditions of acoustic shielding in the region of the mental foramina over the whole frequency band of the dolphin's hearing. Therefore, the mental foramina of its lower jaw take part in receiving and conducting the sounds into the mandibular fat in the entire frequency range of the dolphin's hearing. The obtained results give an experimental proof for the assumption that the morphological structures of the lower jaw play a role of the peripheral part of a dolphin's hearing. Now there are grounds to assume that Odontoceti have the similar peripheral part of their hearing. This assumption is based on the similarity of their morphology.