A narwhal’s tusk serves multiple purposes: it’s a sensory organ that detects changes in the surrounding water, a signal of size and strength during competition between males, and occasionally a tool for stunning prey. Scientists debated the tusk’s function for centuries, but research over the past two decades has revealed it’s far more sophisticated than a simple weapon or ornament.
The Tusk Is Actually a Tooth
The narwhal’s tusk is a canine tooth that grows outward through the animal’s upper lip in a distinct counter-clockwise spiral. It originates from the left side of the upper jaw, where canine teeth sit in all mammals. The right canine also exists but stays embedded in the skull, never erupting. In rare cases (less than 1% of males), both teeth erupt, producing a double-tusked narwhal.
Nearly all males grow a tusk, while only about 1.5% of females do. The tusk can reach up to 9.8 feet long and weigh over 20 pounds. Unlike most teeth, it’s covered in a tissue called cementum, which normally only appears around the base of a tooth buried in bone. The whole structure is softer and less mineralized than human teeth, with mechanical properties closer to reindeer antler. That flexibility allows it to absorb lateral impacts without snapping.
A Giant Sensory Antenna
The most surprising discovery about the narwhal tusk is that it works as a sense organ. Most teeth have nerves buried deep inside, protected by hard enamel. The narwhal tusk is built in reverse: a rigid rod in the center surrounded by a porous, flexible outer layer. An estimated 10 million fluid-filled channels called tubules run from the inner nerve core to the tusk’s outer surface, creating a direct connection between the narwhal’s nervous system and the surrounding ocean.
A research team led by Martin Nweeia at Harvard tested this sensory function directly. They ran water of varying salt concentrations over live narwhal tusks and measured the animals’ heart rates with portable monitors. The narwhals showed significant heart rate changes depending on water salinity, confirming that the tusk detects real environmental information and transmits it to the brain. It was the first tooth in any animal proven through live testing to sense a normal variable in its environment. The tusk can also detect subtleties in temperature, pressure, and particle concentration in the water.
For an Arctic whale that navigates shifting sea ice and needs to find pockets of open water, this kind of environmental awareness could be a real survival advantage. Changes in salinity can signal the presence of freshwater from melting ice or the boundary between different water masses where prey congregates.
A Signal of Size and Strength
The strongest evidence points to the tusk as a sexually selected trait, meaning it evolved primarily because it helps males compete for mates. A study published in Biology Letters found that narwhal tusks grow disproportionately large compared to body size, a pattern biologists call hyperallometry. This is a hallmark of traits shaped by sexual selection, because the signal being sent is straightforward: “I am bigger than you.”
Male narwhals engage in a behavior called tusking, where two animals cross and rub their tusks together. This appears to be a ritualized way of sizing each other up without resorting to a real fight. The idea is that most contests get settled through signaling alone, sparing both animals the risk of injury.
But real fights do happen. Adult males carry significantly more scars on their heads than juvenile males or females, similar to scarring patterns in other whale species known to fight. And 40 to 60% of adult males have damaged or broken tusks, which is exactly what you’d expect if tusks were being used in physical confrontations. The tusk can withstand sideways strikes without breaking, thanks to its flexible, antler-like composition, but it’s not indestructible. The current consensus is that the tusk functions as both a visual signal and an actual weapon during disputes between males.
Hunting With the Tusk
For a long time, scientists weren’t sure narwhals used their tusks to catch food. Narwhals feed primarily on Arctic cod, Greenland halibut, and squid, and they were thought to simply suck prey into their mouths. But a 2025 study published in Frontiers in Marine Science captured drone footage of narwhals using their tusks to hit fish with rapid, forceful strikes, enough to stun or possibly kill them before eating.
The footage showed two distinct patterns. In some cases, narwhals gently tapped or investigated objects with the tusk, suggesting exploratory or playful behavior. In others, they delivered multiple hits in quick succession with enough force to incapacitate fish. This was the first documented evidence that narwhals actively use the tusk as a foraging tool, adding a practical hunting function to its list of roles.
Why One Tooth Does So Many Things
The narwhal tusk is unusual because it doesn’t fit neatly into a single category. Elephant tusks are primarily tools for digging, stripping bark, and fighting. Walrus tusks help haul their owners onto ice and establish dominance. The narwhal tusk does some of those things, but it also functions as a sensory instrument with no real parallel in other animals. Those 10 million tubules connecting the nervous system to the ocean make it something closer to an antenna than a weapon.
The fact that nearly all males have one while almost no females do confirms that sexual selection is a major driver of its existence. But the sensory capabilities suggest it wasn’t shaped by mating competition alone. A tusk that can read water salinity, temperature, and pressure gives the narwhal real information about its Arctic environment, information that matters whether or not another male is nearby.