http://mentalfloss.com/article/55994...about-narwhals
There are few creatures I find so fascinating as the narwhal. Like many tusked animals, this arctic whale has a majestic quality to it. In medieval times, its long, straight tusk was often given to royalty, passed off as a “unicorn horn.” In the 16th century, a narwhal tusk worth £10,000 was given to Queen Elizabeth. Today, the narwhal still holds our interest, and its tusk remains one of the most mysterious things about these creatures. Here’s what we know about them.
1. Its tusk is actually a tooth
While it might appear to be situated in the center of its head, the narwhal’s tusk is actually an exaggerated front left tooth that protrudes from the upper lip. The right front tooth is small, and usually remains in the mouth. Stranger still, while most teeth (including human teeth) have a hard exterior and a soft, sensitive interior, narwhal teeth are the opposite. “No big surprise. It's been opposite in every other way,” Martin Nweeia, a clinical instructor at the Harvard School of Dental Medicine, told NPR after making this discovery. “But to find a tooth that is soft on the outside and has its most dense part around the pulp was completely odd.”...
4. We’re not entirely sure what it’s for
History has numerous explanations for the narwhal’s massive tusk. One theory is that it can be used as a weapon, though this claim lacks sufficient evidence. Another suggests it is an accessory for finding mates and asserting dominance, much like peacock feathers or deer antlers. But the most recent theory, produced by Nweeia and his team, suggests it acts as a sort of environmental sensor. According Nweeia’s research, the tusk is porous and full of nerves, taking in external stimuli like water pressure, temperature, and salinity, and sending information back to the brain. To test this theory, Nweeia fitted narwhals with a kind of “jacket” that insulated the tusk from environmental factors. Then, researchers pumped the jacket full of water samples of varying salinity levels to mimic different kinds of sea ice. They found that different levels of salinity caused the narwhals’ heart rates to fluctuate, indicating they could sense the change and had a physical reaction to it. “But regardless of the reason, the results suggest that narwhals can funnel water into their tusks to measure its salt concentration,” Nweeia said....
7. There are none in captivity
Unlike their close relatives, beluga whales, narwhals do not thrive in captivity. In the '60s and '70s, several attempts at capturing and keeping narwhals resulted in all of the animals dying within several months. In fact, all narwhals kept in captivity have died. Some animals simply aren’t meant to be captured.
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