The Ins and Outs of the Narwhal's Tusk

Scientists have long wondered what narwhals do with their tusk. Do they use this unwieldy appendage, which was once sold as the mythical unicorn's horn and can measure up to nine feet, to fight, spear fish, woo females, or break through ice floes? 

Now, Harvard dentistry researcher Martin Nweeia and his colleagues at the National Institute of Standards and Technology report that the tusk might be a sophisticated sensor with which narwhals closely monitor their environment. Unlike elephant and hog tusks, the narwhal tusk is straight and grows out as a tight spiral similar to an elongated snail shell. Derived from the animal's left incisor, the tusk contains all the layers normally found in teeth. 

But, as the scientists reported at the 16th Biennial Conference on the Biology of Marine Mammals held last week in San Diego, the layers are inside out. Hard layers that normally protect teeth from physical blows and cold shocks are inside, where they lend strength and flexibility to the long, thin tusk. On the outside are softer layers perforated by myriads of tiny canals called tubules connected to nerves. The scientists propose that the tubules serve as sensory organs that can relay information about water temperature, pressure, and salinity to the narwhal's brain.