Additional data on the lower jaw morphology in odontocetes: Panbone thickness

Abstract

The mandibular hypothesis by Norris (1968, 1969) mandible implies that in odontocetes, sounds pass to the ear through a mandibular window (panbone) where the bone is fairly thin and the intra-mandibular fat body. However, thickness of the bone depends on size of the animal. In small and medium-sized odontocetes it is 0.57 to 2 mm, whereas in large ones, such as the killer whale, it attains 5.48 mm (Nummela et al., 2007), which may worsen the conditions for sound penetration into the fatty body. Despite the thick panbone region, the hearing of the killer whale is not inferior to that of smaller odontocetes. These facts encouraged us to obtain additional data on the lower jaw morphology. We 3-D-scanned and analyzed 19 mandibles from adult odontocetes of various species: the porpoises, Irrawaddy dolphin, common dolphin, bottlenose dolphin, beluga, and killer whale. The panbone thickness was measured in all the samples. Results of the study did not reveal a direct correlation of the body size and panbone thickness. Further, the obtained data will be useful for making a mathematical model of sound conduction dependence on the panbone thickness. [Work supported by the Russian Science Foundation, Grant # 17-74-20107 to E.V.S.]The mandibular hypothesis by Norris (1968, 1969) mandible implies that in odontocetes, sounds pass to the ear through a mandibular window (panbone) where the bone is fairly thin and the intra-mandibular fat body. However, thickness of the bone depends on size of the animal. In small and medium-sized odontocetes it is 0.57 to 2 mm, whereas in large ones, such as the killer whale, it attains 5.48 mm (Nummela et al., 2007), which may worsen the conditions for sound penetration into the fatty body. Despite the thick panbone region, the hearing of the killer whale is not inferior to that of smaller odontocetes. These facts encouraged us to obtain additional data on the lower jaw morphology. We 3-D-scanned and analyzed 19 mandibles from adult odontocetes of various species: the porpoises, Irrawaddy dolphin, common dolphin, bottlenose dolphin, beluga, and killer whale. The panbone thickness was measured in all the samples. Results of the study did not reveal a direct correlation of the body size and panbone thic...