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Mystery of the narwhal tusk.

THE NARWHAL TUSK has inspired association with the fabled unicorn and at one time was a highly valued trade commodity. Queen Elizabeth I reportedly paid 10,000 pounds, the 16th century equivalent to the cost of an entire castle, for a single tusk. Yet for hundreds of years, the function of the narwhal's tusk has remained a mystery.

Recently, Harvard dental researcher Martin Nweela and a multidisciplinary team of scientists and Inuit elders working in the Canadian Arctic uncovered evidence that the tusk may serve as a sensor. Abundant nerve endings connected to the outer surface of the tusk could allow the whale to detect minute changes in water temperature, pressure and chemical gradients.

The narwhal (Monodon monoceros) is a large-toothed whale that inhabits Arctic waters. It is characterized by a large spiralled tusk or tooth issuing approximately two to three metres straight out from the left side of its upper jaw. While the male almost always has a tusk (sometimes two tusks), the female usually does not.

Nweela assembled the Narwhal Tooth Expedition in 1990 after rejecting the standing explanations of the tusk's function. The ruling hypothesis was that the tusk demonstrated individual fitness and was used to establish dominance. Like the antlers of deer, males were thought to use their tusks to joust with each other for social hierarchy.

Nweela felt his own observations of the animals did not bear out this hypothesis. Although male narwhals were observed to gently rub their tusks together, the activity was placid and the social implications were not clear. The tusk was also previously thought to assist in ice breaking; however, it is now known that the whales use the backs of their heads to break ice.

The tusk's capacity to act as a sensor was determined through the examination of two freshly harvested male tusks under a scanning electron microscope. Researchers identified over 106 tubules (usually associated with pain reception in teeth) and ten million nerve endings in the tusk, indicating the tusk's ability to behave like a membrane with an extremely sensitive surface. Stress tests performed on the tusks also revealed a surprising degree of flexibility and strength.

Currently, a limited harvest of narwhals by Inuit is allowed in Canada; however, the narwhal is listed in Appendix 11 of the Convention on International Trade in Endangered Species.

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Title Annotation:Science Desk
Author:Bobechko, Liann; Stockton, Steve
Publication:Alternatives Journal
Geographic Code:1CANA
Date:Jan 1, 2006
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