A Narwhal's Tusk Is Actually a Tooth

Long hailed as the "unicorn of the sea," the narwhal's most striking feature is not a horn, but an extraordinary canine tooth. In most males, the left canine grows in a distinct spiral, piercing directly through the upper lip and extending up to 10 feet. While the right canine typically remains small and embedded in the skull, a few narwhals can be found with two tusks, and a small percentage of females will grow a shorter one of their own. For centuries, these tusks were sold by Vikings (Review) to medieval Europeans as unicorn horns, believed to hold magical properties like neutralizing poison.

Far from being a simple spear for jousting or breaking ice, the tusk is a remarkable sensory organ. It is not a solid structure; rather, it is porous and filled with millions of nerve endings that connect its core to the outer ocean environment. This intricate system allows the narwhal to detect subtle shifts in water temperature, pressure, and salinity. This unique "sense" helps them navigate the dark Arctic waters, locate prey, and find breathing holes in the sea ice, making their tooth an indispensable tool for survival.