Martin Nweeia of the Harvard School of Dental Medicine has cracked the mystery of the narwhal, a bizarre species of Arctic whale with a spiral tusk that resembles a long, pointed horn. Researchers had speculated that the tusk is a weapon, perhaps used as a foil during mating competitions.
But Nweeia finds that the sturdy-looking tusk also seems to function as a delicate sensory organ.
Using a high-powered electron microscope, Nweeia and researchers from the Smithsonian Institution and the National Institute of Standards and Technology discovered that the narwhal's tusk is riddled with millions of tiny tunnels, each about 1/100 the width of a human hair. The tubules allow the nerves and blood vessels in the tooth's interior to come in indirect contact with the cold Arctic waters in which the whale swims.
In humans and all other animals, such nerves become exposed only as a result of decay or gum disease. In narwhals, open tooth nerves can sense temperature, pressure, motion, and the presence of tiny particles in the surrounding water, Nweeia says. He believes that the tusk, which occurs on most males and some females, "could be useful in a lot of ways: for detecting ice formation, aspects of prey, and hormonal signs."