SCI/TECH: Narwhal's Tooth Finally Explained

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The narwhal has a tooth, or tusk, which emerges from the left side of the upper jaw and is an evolutionary mystery that defies many of the known principles of mammalian teeth. The tooth's unique spiral, the degree of its asymmetry to the left side, and its odd distribution among most males and some females are all unique expressions of teeth in mammals. The narwhal is usually 13 to 15 feet in length and weighs between 2,200 and 3,500 pounds. Its natural habitat is the Atlantic portion of the Arctic Ocean, concentrating in the Canadian High Arctic: Baffin Bay, Davis Strait, and northern Hudson Bay. It is also found in less numbers in the Greenland Sea, extending to Svalbard to Severnaya Zemlya off the coast of Russia.

Nweeia has discovered that the narwhal's tooth has hydrodynamic sensor capabilities. Ten million tiny nerve connections tunnel their way from the central nerve of the narwhal tusk to its outer surface. Though seemingly rigid and hard, the tusk is like a membrane with an extremely sensitive surface, capable of detecting changes in water temperature, pressure, and particle gradients. Because these whales can detect particle gradients in water, they are capable of discerning the salinity of the water, which could help them survive in their Arctic ice environment. It also allows the whales to detect water particles characteristic of the fish that constitute their diet. There is no comparison in nature and certainly none more unique in tooth form, expression, and functional adaptation.

"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?" says Nweeia. "Such a finding is startling and indeed surprised all of us who discovered it." Nweeia collaborated on this project with Frederick Eichmiller, DDS, director of the Paffenbarger Research Center at the National Institute of Standards and Technology, and James Mead, PhD, curator of Marine Mammals at the National Museum of Natural History of the Smithsonian Institution.

Results from the team's research already has practical applications; studies about the physical makeup of the tusk, which is both strong and flexible, provide insight into ways of improving restorative dental materials. (An 8-foot-long tooth can yield one foot in any direction without breaking). Nweeia also leads the Narwhal Tooth Expeditions and Research Investigation, founded in 2000, which combines scientific experts with Inuit elders, who have collected notes for hundreds of years, to discover the purpose and function of the narwhal tusk.




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