Researchers solve whale tooth mystery: It’s a sensor

By Control Engineering Staff January 19, 2006
Eight-ft-long tooth emerging from the head of the narwhal whale is actually a type of sensor, researchers at the Harvard School of Dental Medicine have found.

Researchers have learned that the 8-ft-long tooth emerging from the head of the narwhal (or unicorn) whale is actually a type of sensor. The tooth has hydrodynamic sensor capabilities and can detect changes in water temperature, pressure, and particle gradients. These findings of Martin Nweeia, DMD, DDS, and the Harvard School of Dental Medicine , were reported recently at the 16thBiennial Conference on the Biology of Marine Mammals in San Diego.
The questions of why the animal has the tooth and what is its function has eluded the scientific community for hundreds of years. The tooth, or tusk, emerges from the left side of the whale’s upper jaw and is an evolutionary mystery that defies many known principles of mammalian teeth. The tooth’s spiral, degree of its asymmetry to the left side, and odd distribution among most males and some females are unique expressions of teeth in mammals, the researchers explained. It has ten million tiny nerve connections that tunnel their way from the central nerve of the narwhal tusk to its surface. Though seemingly rigid and hard, the tusk has an extremely sensitive surface.
“Why would a tusk break the rules of normal development by expressing millions of sensory pathways that connect its nervous system to the frigid arctic environment?” asks Nweeia. “Such a finding is startling and indeed surprised all of us who discovered it.” Nweeia collaborated on the project with Frederick Eichmiller, DDS, director of the Paffenbarger Research Center at the National Institute of Standards and Technology , and James Mead, Ph.D., curator of marine mammals at the National Museum of Natural History of the Smithsonian Institution .
The narwhal is typically 13-15 ft long and weighs between 2,200 and 3,500 lb. It lives in the Atlantic portion of the Arctic Ocean and in the Greenland Sea. The whales use the tusk to detect particle gradients in, and discern the salinity of, water—capabilities that could help them survive in their Arctic ice environment. The tooth also helps them detect water particles characteristic of the fish they eat. The sensory connections also are capable of tactile ability. Researches noted that narwhals are known for rubbing tusks, which likely causes them to experience “a unique sensation.”
Results of the findings are expected to have practical application to restorative dental materials and help design new experiments for the study of these mammals.

—Jeanine Katzel, senior editor, Control Engineering,