A study of dolphin jaw anatomy suggests their teeth might act as antennae for sound waves, potentially helping to explain how they hear and use echolocation underwater.
鈥淥ur findings support the hypothesis that dolphins utilise their teeth as part of an advanced sound reception system,鈥� says at Tsurumi University in Japan. 鈥淭his finding provides insight into how dentition may be helpful for dolphins鈥� underwater life.鈥�
杏吧原创s have long known that dolphins and other members of the toothed whales group of species, called odontocetes, have unique teeth, many of which aren鈥檛 used for chewing. The reason they have so many teeth is a mystery.
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Many researchers hypothesise that dolphin teeth are well-suited to receive sound waves, says Kodera. The dolphin cochlear nerve, a vital part of the inner ear which processes auditory stimuli, connects to fat in the mandible, or lower jaw, of the dolphin, suggesting that their teeth might act as an interface between sound vibrations in the water and the pathway to the brain.
To better understand dolphin teeth and their relationship to the underlying jaw, Kodera and his team investigated mandibles from several odontocete species, including the bottlenose dolphin (Tursiops truncatus), striped dolphin (Stenella coeruleoalba), Pacific white-sided dolphin (Lagenorhynchus obliquidens) and false killer whale (Pseudorca crassidens). They also examined the jaws of domestic pigs (Sus scrofa domesticus) as a comparison.
They identified several unusual features in odontocete jaws. The teeth sit more loosely within the jaw than in other mammals, and the alveolar sockets, which hold the teeth, are spongier and more porous than those in land mammals. Most importantly, they discovered that long and thick bundles of nerve fibres connect to the teeth through these porous structures.
鈥淭hese long fibres indicate significant tooth mobility, while the thick nerve bundles suggest heightened sensitivity to tooth movement,鈥� says Kodera.
The nerve bundles in dolphins had many sensory receptors at their ends and were wrapped in a thick layer of fatty insulation, which is a feature that helps electrochemical signals travel more quickly through nerve fibres. The fibres are thicker than those in land mammals, suggesting the teeth might have a sensitivity comparable with tactile hairs used by some animals to sense touch, says Kodera.
at the University of Bath, UK, who wasn鈥檛 involved with the study, says the results don鈥檛 necessarily show which senses the fibres might aid. 鈥淭his would need to be borne out from other studies,鈥� he says.
Kodera acknowledges the findings aren鈥檛 conclusive evidence of a direct role in echolocation or underwater hearing. 鈥淔uture research should focus on direct physiological and biomechanical studies,鈥� he says.
The results are 鈥渆ye-opening鈥�, says at the University of California Museum of Paleontology in Berkeley. He would like to see the fibres tested in living dolphins to better understand their purpose. 鈥淚 will certainly have this study in mind any time I鈥檓 looking at dolphin mandibles and tooth sockets moving forward,鈥� he says.
The Anatomical Record
