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Part - 2

In 2000, Dr. Nweeia decided to investigate the animal closely and first trekked to its icy habitat in 2002, going to Pond Inlet, a tiny settlement at the northern tip of Baffin Island. There he met David Angnatsiak, an Inuit guide who agreed to help. Under international agreement, the Inuits are allowed to hunt narwhals, which they eat and harvest for their tusks.

During expeditions in 2003 and 2004, aided by the Canadian Department of Fisheries and Oceans, Dr. Nweeia was able to gather head and tusk specimens, which he brought back for analysis. He and his colleagues tracked a clear nerve connection between the animal's brain and tusk, finding the long tooth heavily innervated. But why it should be so remained a mystery.

The investigators zeroed in on the riddle with sophisticated instruments at the Paffenbarger Research Center of the National Institute of Standards and Technology, a federal organization in Gaithersburg, Md. The American Dental Association finances the research center.

Rough deposits of calcified algae and plankton coated the outside of the tusks Dr. Nweeia brought back. The scientists decided to remove them in an acid bath to get down to the surface of the tooth before viewing it under an electron microscope. First, however, they decided to give the uncleaned tusk a cursory microscopic examination.

It was a shock. There, contrary to all known precepts of tooth anatomy, they found open tubules leading down through the mazelike coating to the tooth's inner nerves and pulp.

"That surprised us," recalled Frederick C. Eichmiller, director of the Paffenbarger Research Center. "Tubules in healthy teeth never go to the surface."

Extrapolating from a count of open tubules over one part of the tooth's surface, the team estimated that the average narwhal tusk had millions of openings that led down to inner nerves.

"No one knew that they were connecting to the outside environment," Dr. Nweeia said. "To find that was extraordinary."

His collaborators include Naomi Eidelman and Anthony A. Giuseppetti of the Paffenbarger Research Center, Yeon-Gil Jung of Changwon National University in South Korea and Yu Zhang of New York University.

Increasingly, the investigation centers on how the whales use their newly observed powers. One central unanswered question is how sensory abilities in males might relate to herd behavior and survival.

The scientists, noting that the males often hold their tusks high in the air, wonder if the long teeth might sometimes serve as sophisticated weather stations, letting the animals sense changes in temperature and barometric pressure that would tell of the arrival of cold fronts and the likelihood that open ice channels might soon freeze up.

Dr. Nweeia noted that the discovery does not eliminate some early theories of the whale's behavior. Tusks acting as sophisticated sensors, he said, may still play a role in mating rituals or determining male hierarchies.

He added that the nerve endings, in addition to other readings, undoubtedly produce tactile sensations when the tusk is rubbed or touched, and that these might be interpreted as pleasurable.

This tactile sense might explain why narwhals engage in what is known as "tusking," where two males gently rub tusks together, Dr. Nweeia said. He added that the Inuit seldom report aggressive contact, undermining ideas of ritualized battle.

Dr. Nweeia said that gentle tusking might also be a way that males remove encrustations on their tusks so tubules stay open, allowing them to better function as sensors. "It may simply be their way of cleaning or brushing teeth," he said.

He called the basic discovery mind boggling, especially given the freezing temperatures of the Arctic.

"This is one of the last places you'd expect to find such a thing," Dr. Nweeia said of the large sensory organs. "Cold is one of the things that tubules are most sensitive to," as people sometimes discover when diseased gums of human teeth expose the tubules.

"Of all the places you'd think you'd want to do the most to insulate yourself from that outside environment," he said, "this guy has gone out of his way to open himself up to it."



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