The "unicorn of the sea," narwhals are among the most elusive and mysterious marine mammals. These Arctic whales are known for their trademark "horns" — and now scientists are getting closer to understanding these incredible creatures.

What is the horn, anyway?

A narwhal's horn, or tusk, is actually a Narwhal illustrationcanine tooth that extrudes (up to 9 feet in males!) through the top of the whale's mouth. Another tooth accompanies it, inside the mouth, so it's actually a pair of teeth; one of only two pairs in the mammal's mouth.

Naturally, this makes the narwhal an interesting subject for dental researcher and marine biologist Martin Nweeia. Nweeia, a researcher at Harvard School of Dental Medicine and a practicing dentist, has studied these creatures for the greater part of 15 years — and he says that these teeth aren't just for show; they are sensory organs.

Up until now, scientists have surmised that the great jutting tooth is a product of sexual selection, used to attract the lady narwhals. But Nweeia and his team have published a study in The Anatomical Record that claims to have found a link between this tooth and the brain.

How could a tooth sense the environment?

Even human teeth are connected to nerves, although ours are protected by strong outer layers. Narwhals's teeth, on the other hand, appear to have it backwards: the tusk has channels that allow seawater to enter the interior of the tooth. In short, the porous surface of a narwhal's tusk allows water to wash over nerves that directly connect the information to the mammal's brain.

Nweeia's study says that the tusk is composed of genetic and neurological features that are associated with sensory functions in other instances. Being able to detect levels of salt in seawater could help the animals navigate to find food and even mates in their ever-changing Arctic environment.

Nweeia and his team were able to collect this information by measuring live narwhals' heart rates with portable devices, and measuring salinity with a "tusk jacket." And when salt concentration changed in the water, so did the narwhal's heart rate.

Questions remain

Other scientists have not ruled out that the horn is simply a tool for attracting mates, much like a peacock's feathers. And it's possible that the whales' fluctuating heart rates could have resulted from the stress of capture, argues Kristin Laidre, a marine mammal biologist at the University of Washington in Seattle.

Laidre is also skeptical of Nweeia's conclusions because the large teeth ultimately would only be advantageous as sensory organs for male narwhals.

"In mammals, females are critical to helping populations grow," she told National Geographic. "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 are the next steps? Nweeia plans on learning as much as possible about the Inuit's traditional knowledge of the marine mammal, continuing the quest to make sense of this enigmatic animal.

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Photo credit: Wikimedia Commons