What is the Function of Narwhal's Tooth?

The narwhal is a small, rare arctic whale with a very long (~7-10 ft, or 2-3 meters) tooth that resembles the horn of the fabled unicorn. It has been used to adorn palaces and royal scepters around the world, from England to Japan. The ground tooth of a narwhal has (falsely) been said to cure various diseases. But until recently, the function of this tooth has been a mystery -- the means of its evolution defies normal models of the way mammalian teeth develop.

In 2005, Harvard School of Dental Medicine researcher Martin Nweeia determined the function of the tooth. It acts as a sophisticated hydrodynamic sensing device, capable of measuring temperature, water particle density, salinity, and other information. Although one would imagine a tooth that looks like a horn to be rigid, it has a delicate, membrane-covered surface saturated with millions of sensory nerves. These neural networks feed directly into the central nervous system of the narwhal, giving it a uniquely powerful sensory apparatus for survival in the arctic environment.

The tooth of the narwhal is unique among mammals, which partially explains why it has taken science so long to figure it out. The spiral tusk morphology is unique to narwhals, for example. Also, the tusk is common among males but rare among females, an unusual asymmetry for mammalian teeth.

Before the purpose of the tusk was decisively determined, a number of theories were advanced to explain its purpose. These included a tube for breathing, a heat sink, a swimming rudder, a display for mating, and even a tool to break ice. Because the animal is so rare and lives in such cold areas, there has been a lack of samples with which to make theories. A collaborative effort between Nweeia and the Inuit people of Canada led to a large catalog of behavior of the animals, helping the final determination of the tusk's function.

The primary function of a narwhal's tooth, specifically the elongated left canine seen in males, is believed to serve several roles. It is a sensory organ with millions of nerve endings that may detect changes in the environment, such as water temperature, pressure, and salinity. Additionally, it's thought to play a role in mating rituals and establishing dominance hierarchies among males.

Narwhals typically have two teeth. In males, one of these teeth grows into the iconic spiral tusk, while the other remains vestigial inside the skull. In some rare cases, both teeth in males can develop into tusks. Females usually have two rudimentary teeth that do not erupt.

Yes, female narwhals can have a tusk, but it is a rare occurrence, with only about 15% of females displaying this trait. When present, their tusks are usually smaller and less spiraled than those of males, and the reasons for their development are not as well understood.

A narwhal's tusk can grow up to 10 feet long, making it one of the most distinguishing features of the species. The length of the tusk can indicate a male's age and physical condition, which may be a factor in female mate selection, suggesting that longer tusks could be a sign of genetic fitness.

There is little evidence to suggest that narwhal tusks are used for hunting. Observations and studies indicate that narwhals primarily use suction to feed on fish, squid, and shrimp, rather than employing their tusks as tools for capturing or spearing prey.

Climate change poses a significant threat to narwhals, impacting their Arctic habitat and potentially altering the sensory functions of their tusks. As sea ice diminishes, narwhals may face changes in prey availability and increased exposure to predators and human activities, which could affect their feeding behaviors and the utility of their tusks in their changing environment.