While the exact purpose of the narwhal’s famous tusk or horn – which is actually a tooth that has grown beyond the jawline – the long-held belief in marine mammal communities was that the tusk was used by males (the only narwhals that grow have the elongated tooth) to establish dominance. The sight of narwhals “dueling” with their “swords” at the water’s surface helped underscore this theory.
But in March 2014, Harvard researchers published a paper that proposed a controversial, new theory: the tooth, which can grow up to 9 feet (2.7 m) is actually a sensory organ that allows the cetacean to “taste” the water to detect prey, water temperature and other threats. While researchers have known that the narwhal’s tooth is not covered in enamel like other teeth, the Harvard research claims to explain why. According to the new theory, water enters the tusk and travels through channels to the base of the brain, where nerve endings are able to “read” the chemical composition of the water and determine the salt levels, water temperature and other important information.
The teeth of mammals do not have any channels that connect teeth to sensory organs. Anyone who has experience the pain of a root canal can attest to the reason why this is so – having nerve endings exposed to the elements can be extremely painful. The narwhal’s long tooth is completely different, argues the Harvard study, and allows the cetacean to draw information from the water instantly, without needing sight, sound, smell or echolocation to understand its environment.
Traditional mammal scientists argue that the Harvard study is wrong and that the tusk of narwhals is used for more traditional purposes, such as establishing male dominance. The biggest pushback against the Harvard study, mammalogists argue, is that only male narwhals traditionally grow the famous tusk (female narwhals with a tusk are uncommon, though they have been documented). If a narwhal used its tooth to “taste” or “read” the water, it would be more logical for the females to display this ability to protect offspring, not the males.
“In mammals, females are critical to helping populations grow,” University of Washington marine mammal biologist Kristin Laidre said. “So there’s no way that females wouldn’t have a sensory organ that would help them survive or give them sort of an advantage in terms of finding food.”
So what’s the ultimate answer to what is a narwhal’s tusk used for?
We don’t know.