Narwhals, often called the “unicorns of the sea,” are Arctic whales known for their distinctive, sword-like tusk. This prominent feature has long been a subject of scientific inquiry into its nature and functions in their challenging environment.
The Narwhal’s Distinctive Dentition
Narwhals typically have only two teeth. In most males, the upper left canine elongates significantly to form the prominent tusk. The scientific name, Monodon monoceros, meaning “one tooth, one horn,” reflects this characteristic. The other tooth usually remains rudimentary, embedded in the skull. This tusk is an overgrown tooth, not a horn, distinguishing narwhals from other toothed whales with full sets of teeth.
Unraveling the Tusk’s Purpose
The narwhal’s tusk serves multiple functions. Primarily, it acts as a sensory organ, containing millions of nerve endings. This allows it to detect changes in water salinity, temperature, and pressure, aiding navigation, food location, and identifying mating grounds. The tusk is also used in foraging; drone footage shows narwhals striking and stunning fish, making them easier to capture and consume.
Furthermore, it plays a role in social interactions, particularly among males. “Tusking” behavior, where narwhals rub their tusks, suggests communication or a ritualistic display to assess dominance. The tusk is also linked to male-male competition and sexual selection. Males with longer tusks tend to be more successful in contests, signaling fitness and social status. Some functions are still being investigated.
Tusk Growth and Peculiarities
The narwhal tusk exhibits a remarkable growth pattern and internal structure. It grows continuously throughout the animal’s life, with new layers of dentin and cementum added annually, similar to tree rings. This growth contributes to its impressive length, which can reach up to 3 meters (10 feet). Uniquely, the tusk grows in a left-handed spiral, helping maintain its straightness.
The tusk’s internal composition is inverted compared to typical mammalian teeth. Unlike human teeth with hard enamel, the narwhal tusk has a softer, porous outer layer of cementum. This allows seawater to reach inner pulp nerve endings, contributing to its sensory capabilities. While predominantly a male trait, 3% to 15% of female narwhals can also develop a tusk, though typically shorter and less spiraled. Two tusks are rarer, found in about 1 in 500 males, and exceptionally in females.