Tusks could be multifunctional: a good tusk could be a useful sensor, and as a result females might decide "that guy's got a great tusk, I'm going with him. That makes them difficult to study, so perhaps it is not surprising that misconceptions abound. A normal tooth, or even tusk, is tough on the outside, and soft on the inside. There are also a few "double tuskers": males that have two tusks rather than one, for unknown reasons. "The tusk is most common in males and is only infrequently found in females," says Westdal. That's why we've put together these 8 reasons for why your mouth … They also use sonar to navigate. (Photo by Chip Clark, Smithsonian Institution)There are many kinds of curious expressions of teeth in whales, narwhals being the most extraordinary, Nweeia says. Spearing these animals would be really difficult, and even if a narwhal managed it, it would not have any other appendages long enough to retrieve the fish from its tusk.Many people also have the idea that narwhals chew their food. (Photo by Joseph Meehan)“It is striking when you think that this animal decided to take all of its tooth-producing energy and put it into one thing [a tusk] that sticks out nine feet into the ocean. Maybe it is an aggressive weapon for narwhal-narwhal battles, or for fending off predators. Incredibly, the narwhal’s only visible tooth is outside of its mouth. "We don't know the answers to this at all," says Westdal. 9. Its tusk, in fact, is a giant canine tooth—that can grow as long as 9 feet—with a distinct left-hand spiral, covered in a tissue called cementum, normally only found around the base of a tooth lodged in bone. It could also be an icebreaker, a digging tool, or a way to show off to females.To solve this puzzle, Nweeia has assembled a team that includes marine and developmental biologists, comparative zoologists, dentists, and orthopedic surgeons.In a 2014 study that is perhaps the most detailed and high-tech analysis of the tusk ever attempted, "This tooth is almost like a piece of skin in the sense that it has all these sensory nerve endings," says Nweeia. That is not seen in other mammalian teeth except when they are diseased. Inside the narwhal’s mouth, there are no teeth. As the Arctic sea ice retreats due to global warming, ever more shipping is passing through the Arctic, and that means it is getting noisier.That could be a problem for narwhals. Also, the tusk has a straight axis and a spiraled morphology. Narwhals feed mainly on Greenland halibut, Arctic and polar cod, squid and shrimp. "In all the encounters I've had with them, they are beautiful… and quite graceful," she says. But when a dentist peers into the mouth of an Arctic narwhal, all bets are off.The mouth of a narwhal has no teeth. In all the encounters I've had with them, they are beautiful… and quite graceful The narwhal tusk is "essentially built inside out," says Nweeia. Unlike our own teeth, it is soft on the outside, and gradually gets hard and dense on the inside.Nweeia's team showed that the tusk can sense changes in the salinity of the water, suggesting that it is a giant, antennae-like sensor.That is a little tricky to explain. (Photo by Martin Nweeia)Incredibly, the narwhal’s only visible tooth is outside of its mouth. It is a mainly male feature, but occasionally female narwhals have one. Females will give birth to a calf once every 3 years. Close inspection across many specimens reveal extreme variation in location, morphology and histology (tissue structure) of these teeth, all indications they “are following a pattern consistent with evolutionary obsolescence,” the scientists write.An array of vestigial teeth collected from narwhals. Anyone who believes this needs to think through the practicalities, says Narwhal tusks can grow to lengths of 2-3m, and they eat relatively small prey like halibut, shrimp and squid.

On top of all that, their tooth structure is all wonky.

The horn can grow as long as nine feet. 5. A lot of people think this whale has teeth in its mouth, and it has none Perhaps the most pervasive myth about the tusk is that narwhals use it to spear food. That is not particularly surprising, as humans have hunted them for centuries. From left, James Mead, curator emeritus, Museum of Natural History; Ted Cranford, San Diego State University; and Martin Nweeia.

“With whales the evolutionary pieces of the puzzle are scant and I prefer to leave speculation out of the equation.”The dissection team at the Osteo-Prep Lab of the Smithsonian’s National Museum of Natural History begins dissection on a male narwhal specimen.