Martin Nweeia, a researcher at the Harvard School of Dental Medicine (HSDM), has answered a marine science question that has eluded the scientific community for hundreds of years: why does the narwhal have an 8-foot-long tooth emerging from its head, and what is its function? Nweeia, a clinical instructor in restorative dentistry and biomaterials sciences at HSDM, presented his conclusions at the 16th Biennial Conference on the Biology of Marine Mammals in San Diego last month. 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. 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. '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.'
In the past, many theories have been presented to explain the tooth's purpose and function, none of which have been accepted as definitive. One of the most common is that the tooth is used to display aggression between males, who joust with each other for social hierarchy. Another is that the tooth is a secondary sexual characteristic, like a peacock's feathers or a lion's mane.
Nweeia's findings point to a new direction of scientific investigation. 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.
Rights and permissions
About this article
Cite this article
Mystery of world's strangest tooth solved. Br Dent J 200, 8 (2006). https://doi.org/10.1038/sj.bdj.4813157