How Narwhal Tusks Grow and What They Do

How an upper-jaw tooth becomes a spiral tusk

A narwhal’s tusk is an elongated canine tooth that projects from the left side of the upper jaw. Narwhals have two teeth in the upper jaw, and in females these usually remain embedded in the upper jawbone. In males, the left tooth normally begins growing forward through the front of the jaw at two or three years of age. The usual pattern has documented exceptions: females may have a tusk, while males may lack one or develop two tusks.

At the microscopic level, the tusk is built from mineralised collagen fibrils arranged as two opposing helical structures. Its outer layer forms a left-handed helix, while the layer beneath it forms a right-handed helix. This opposition helps the tooth grow straight even as its exterior develops the large-scale left-handed spiral characteristic of the tusk.

Alongside the tusk, the narwhal has one pair of small vestigial teeth in open sockets in the upper jaw. These teeth differ in form and composition and extend around the exposed sockets at the sides, rear and underside. In males, they are commonly shed into the palate. Their varied shapes and anatomy indicate a path of evolutionary obsolescence.

Size and build: how big narwhals and their tusks get

Adults measure 9.8 to 18.0 feet long and weigh about 1,800 to 3,500 pounds. NOAA gives sex-specific maximums of 13.8 feet and 2,204 pounds for adult females, compared with 15.7 feet and 3,527.4 pounds for adult males. On average, males are about 28 inches longer and more than 75 percent heavier than females.

Narwhals have robust bodies, small bulbous heads, short blunt snouts, and little to no beak. Male and female tail flukes differ in shape: males’ are bent inward, while females’ front margins sweep back. The male shape is thought to be an adaptation that reduces drag caused by the tusk. Instead of a dorsal fin, a narwhal has a shallow dorsal ridge, possibly an evolutionary adaptation that makes swimming under ice easier or helps with rolling.

What the tusk is known, observed, and proposed to do

Current scientific consensus indicates that the narwhal tusk is a secondary sexual characteristic associated with sexual selection and indicating social status. Females usually lack tusks yet live longer than males, so the tusk cannot be essential for survival. Its primary function is generally accepted as sexual, while claims about other uses remain debated.

The tusk is also a highly innervated sensory organ with millions of nerve endings, allowing a narwhal to sense temperature variability around it. These nerves may also be able to detect changes in particle concentration and water pressure, and the tusk is thought to help sense water salinity.

Drone footage recorded in Tremblay Sound, Nunavut, in August 2016 showed narwhals tapping and stunning small Arctic cod with their tusks, making the fish easier to catch. Narwhals otherwise capture prey by creating suction with their mouths. Some biologists suggest the tusks are used in fights, while others argue that they may aid feeding; they are also thought to function as weapons or in attracting mates. According to Martin Nweeia, males may rub tusks together to remove encrustations rather than as a display of aggressive male rivalry.

From Arctic resource to traded ‘unicorn horn’

Narwhals have coexisted with circumpolar peoples for millennia. Native peoples of the Arctic hunt them for flesh, blubber and tusks, and their skin, meat, teeth, tusks and carved vertebrae are also traded commercially. About 1,000 narwhals are killed each year, around 600 in Canada and 400 in Greenland. Tusks are sold carved or uncarved.

Based on an analysis of 2007 hunts in Hudson Bay, a 2013 paper estimated gross revenue at CA$6,542 per narwhal. Hunts receive subsidies, but they continue mainly to support tradition rather than for profit.

Vikings and Greenland Norse likely began trading narwhal tusks, which later reached the Middle East and East Asia through European channels. It is unclear whether they hunted narwhals themselves or mainly recovered tusks from animals killed by orcas.

In medieval Europe, the tusks were believed to be horns from legendary unicorns. Considered to have magical properties, they were used to counter poisoning and diseases including measles and rubella, and appeared on staffs and thrones. They were also given as state gifts to kings and queens. Their price was said to have been a couple of hundred times greater than their weight in gold during the 18th and 19th centuries. As modern science rose toward the end of the 17th century and the unicorn notion was scientifically refuted, narwhal tusks were rarely used for magical purposes.