Captured in the Java Sea, this older bottlenose dolphin was carted from town to town, and forced to perform in Indonesia’s now-defunct traveling circus. He was critically underweight, his right pectoral fin was injured, and every one of his teeth was worn below the gum line. "No one has shown that a dolphin can receive sounds through its teeth.Three years ago in 2019, Johnny was rescued from a life of servitude. "It's just a wild hypothesis," says Whitlow Au, a marine biologist at the Hawaii Institute of Marine Biology on Coconut Island in Kaneohe Bay. Strangely, although the system may be useful for man-made sonar devices, whether dolphins actually use it remains controversial. That configuration, Dobbins found, is resilient to frequency changes in the dolphin range. Although the teeth are usually evenly spaced in marine dolphins, those of river dolphins are larger and closer together towards the tip of their long jaws. River dolphins often live in shallow, muddy waters where sight is of little use, and many river dolphins are virtually blind. To investigate this, Dobbins then used his models to compare the impact of the different tooth arrangements found in marine and river dolphins. That could pose a problem for dolphins, because they use a range of frequencies from 50 to 150 kilohertz. Whereas the broadside array loses the ability to determine direction of sound closer than 10 centimetres from the source, the endfire array can still do so.īut the performance of endfire models varied depending on the frequency of the sound. In a broadside array, the sound travels at right angles to the jaw - from directly underneath, for example. The models showed that the endfire-array pattern performs better at close range than the 'broadside' pattern often used in man-made sonar systems. This arrangement, called an endfire array, is commonly used in man-made radio and radar systems, but not in sonar, he says. Model teethĭobbins modelled each jaw as if it were two straight lines of teeth meeting at an angle of 10-20 degrees, and assumed that most of the sound travelled in the same plane as the jaw - with sound coming from in front of the dolphin's nose, rather than from above, below or to the side. Dental vibration could be transmitted to the brain by specialized nerves, scientists have postulated, or to the jaw, which contains specialized fat deposits - sometimes called acoustic fat - believed to help transmit sound waves to the inner ear. The notion helps explain two peculiarities in dolphin dentistry - dolphin teeth are all the same type, rather than being split into incisors for cutting and molars for chewing, and the distance between the teeth is remarkably precise.
Kaneohe Bay, HawaiiĪccording to that theory, dolphin teeth act as an array of receivers that vibrate in response to pressure from sound waves.
Whitlow Au, Hawaii Institute of Marine Biology. To discover why dolphins are so adept at echolocating in shallow water, Dobbins devised models based on the theory that the animals receive some sounds using their teeth. "Dolphins obtain a similar mental 'image' of the surface of a complex object whether they use sonar or vision to look at it," says Elizabeth Taylor, a marine biologist at the National University of Singapore.ĭolphin sonar outperforms any man-made system, particularly in shallow water, where reverberation, water turbulence and suspended sediment make sonar particularly challenging. The results, says study author Peter Dobbins of the engineering firm SEA Group Ltd in Bristol, UK, could be particularly useful for improving sonar in shallow water, making it better at tasks such as searching for naval mines.ĭolphins use sonar for navigation and to echolocate prey by bouncing sound waves emitted as high-frequency clicks off objects in their environment. GettyĪ model of how dolphins may use their teeth to receive sound could provide clues for improving man-made sonar systems, according to a study published in Bioinspiration & Biomimetics 1. Smile: his pearly whites could help him find fish as well as eating them.
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