The narwhal, a whale inhabiting the Arctic waters, is widely recognized for its distinctive elongated protrusion. This unique feature has earned it the nickname “unicorn of the sea,” sparking curiosity about its true nature. Many wonder if this prominent structure is a horn, a specialized tool, or if narwhals possess other dental structures in addition to it. Understanding this remarkable appendage reveals much about this elusive marine mammal.
The Narwhal’s Signature Tusk
The prominent projection from a narwhal’s head is an elongated canine tooth. It typically grows from the left upper jaw in male narwhals, though some females can develop a smaller one. It can reach 1.5 to 3 meters (5 to 10 feet) in length, with some recorded exceeding 3 meters. The tusk displays a unique counter-clockwise spiral pattern along its length.
The tusk’s composition is similar to other teeth, primarily consisting of dentine, a hard, dense tissue, surrounded by cementum. Unlike most mammalian teeth, the narwhal tusk lacks an outer layer of enamel. Its outer surface is porous cementum, containing millions of microscopic tubules filled with fluid and nerve endings that extend almost to the tip. This unusual “inside-out” structure contributes to its sensitivity.
Unraveling the Tusk’s Purpose
The tusk serves multiple functions for the narwhal. Its highly innervated structure acts as a sensory organ, enabling the narwhal to detect subtle environmental changes like water temperature, salinity, and pressure. This sensory capability may assist narwhals in navigating their Arctic habitat and locating prey.
The tusk also plays a role in foraging, with observations showing narwhals using their tusks to tap and stun Arctic cod, making them easier to catch. The tusk is also believed to be involved in communication and social interactions among narwhals. Males have been observed rubbing their tusks together, a behavior known as “tusking,” which may be a form of social display or a way to transfer information. The tusk size can also indicate a male’s fitness and social status, influencing mating dynamics.
Beyond the Tusk: Other Narwhal Teeth
While the prominent tusk is the most striking dental feature, adult narwhals have a limited number of other teeth. Typically, an adult narwhal possesses only two teeth: the elongated tusk and a smaller, rudimentary tooth on the opposite side of the jaw. This second tooth usually remains embedded within the jawbone and does not erupt through the lip.
Narwhals are classified as toothed whales, yet they differ from most other toothed whales, such as dolphins, by lacking a full set of chewing teeth. Their diet, which primarily consists of soft-bodied prey like squid, shrimp, and Arctic cod, does not require extensive chewing. Instead, narwhals create a vacuum to suck up their food, reflecting their specialized feeding strategy in the absence of conventional chewing teeth.
Tusk Growth and Variation
The narwhal’s tusk grows continuously throughout its life, with new layers of material added at its base annually. This continuous growth allows the tusk to reach impressive lengths over time. The annual growth layers within the tusk can provide researchers with valuable information about the narwhal’s diet and environmental conditions throughout its lifespan, similar to tree rings.
While most male narwhals develop a single tusk, variations occur. In rare instances, a narwhal may grow two tusks, which occurs when both canine teeth develop and protrude. Although less common, about 15% of female narwhals can develop a tusk, though these are generally smaller and less spiraled than those found in males. If a narwhal’s tusk breaks, it does not regrow, but the pulp cavity can seal off, allowing the animal to live.