Hidden second spiral found inside narwhal tusks

Narwhals are toothed whales known for their straight, spiraling tusks. While the unicorn belief was debunked long ago, the tusks remain popular souvenirs in Canada and Greenland. Scientists have continued to investigate the unusual structure of these tusks, and the latest study adds a new twist: rather than a single left-oriented spiral, the tusk also has a second spiral inside, oriented in the opposite direction. The CT scan image used in the study was credited to Adrian Rodriguez Palomo.

Inuit legend explains the spiral tusk as the transformed hair of a woman who became a narwhal after being dragged into the ocean by a harpoon rope. Her hair, worn in a twisted knot, gave rise to the tusk. Biologically, the tusk is actually a canine tooth in the left upper jaw of male narwhals. It emerges when males reach two or three years of age and can grow to lengths of 1.5 to 2 meters, or just under 5 feet to 9 feet 10 inches. Some males may develop two long spiral tusks, while rare cases have none at all.

There is a general consensus that the tusks most likely evolved via sexual selection as a form of social status. They are clearly not crucial for survival, since females usually do not develop the tusk—and if they do, the tusks are much smaller with fewer spirals—yet females typically live longer than males. The precise function of the tusk remains a matter of considerable debate, and the newly identified internal spiral adds another layer of complexity to that discussion.