Title: NOAA Ocean Explorer: Tracking Narwhals in Greenland: Biology
Headings: 
The Biology and Ecology of Narwhals
Dr. Kristin Laidre, Polar Science Center
Applied Physics Lab, University of Washington
References:

Content: Instead the male develops a long straight tooth (or tusk) that protrudes 2-3 m out of the upper left jaw. The tooth grows in a counterclockwise spiral. The myth of the unicorn comes from the narwhal tusk. Tusks exported from the Arctic, perhaps by the Vikings, reached Europe, the Mediterranean, and even the Far East as early as the Middle Ages. The tusks were sold without a good description of the animal from which they came. Therefore, this unusual spiral appendage inspired a great deal of fantasy. The purpose of having such a huge tooth has been discussed for centuries. Many suggestions have been made. Some believe narwhals use their tusk to dig in the seafloor or spear prey. Others believe the tusk is used for making holes in sea ice or it is used to determine sea ice thickness.