Narwhal tusk function debated after a new theory by Martin Nweeia and his team of researchers suggests it is used to sense changes in the narwhals’s environment. Biologists were quick to point out that observing narwhal’s has produced very little evidence that this is the case, but Nweeia’s dental medicine background leads him to believe otherwise. The narwhal tusk, which can grow to nine feet long and is most often sported by males, is actually a tooth, and Nweeia thinks that this makes a world of difference when thinking about its function.
Observing the anatomy of the tooth reveals three distinct layers, similar to our own teeth. The external layer covers the softer material called dentin, which covers the pulp of nerves and blood vessels that run through the extremity. In contrast to our own teeth, where there are no connections between the layers due the extreme sensitivity of the nerves contained within, the tusk of the narwhal features small channels at the barriers between each layer that allow sea water to reach the sensitive pulp beneath the tough exterior. Although it seems counterintuitive for an arctic whale to want frigid water to constantly be flowing over exposed nerves, Nweeia theorizes that the function of the narwhal tusk is allowing the narwhal to detect changes in salinity in the water it swims through.
In studies of live narwhals conducted by Nweeia and his team, the heart rate of captured narwhal’s seemed to rise and fall in response to changing levels of salt in the water they occupied. But the narwhal’s tusk function is debated by biologists who point out that a feature that imparts such as helpful ability would be available to females as well as males, especially since as mammals the narwhals are critically dependant on females to maintain their population. Although some females have been seen with tusks of their own they are most often quite short, only the males have ever been seen with the iconic long spiral tooth.
While there is agreement that being a tooth the tusk is indeed sensitive, it is contended that the conclusion of being able to detect changes in salinity was the reason for the change in heart rate in captured narwhals. As many know, animals tend to be stressed when captured, and the narwhals studied by Nweeia and his team had just been caught in nets and taken to shallow water for observation. Biologists believe that the change in heart rate that was observed had less to do with changing salt levels and everything to do with the whales being observed in a stressful environment.
As it stands, the official explanation is that the tusk is used to attract a mate, similar to bright plumage or impressive antlers. Due to their rarity and elusive nature, narwhals are difficult to capture and even more difficult to study, which may make it impossible to ever know for sure what the exact use of the tusk is. As the narwhal tusk function is debated between biologists and dentists, everyone involved may be long in the tooth before a conclusive answer is found.
By Daniel O’Brien
Sources
National Geographic
Wired
BBC News
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