The tusk is actually an overgrown, twisted front tooth. In its paper, Nweeia’s group showed that the innervated tooth is porous. When the researchers dipped the tusks of captured narwhals into waters of varying salinity, the whales’ heart rates changed: higher salinities resulted in a faster beat. “This is the first time that someone has discovered sensory function [for the tusk] and has the science to show it,” Nweeia told the BBC.
That the tusk can transmit environmental stimuli is not surprising. “The narwhal tusk is a tooth, and teeth are sensitive,” Kristin Laidre, a marine mammal biologist at the University of Washington, told National Geographic. But although some scientists were “dazzled” by the data, according National Geographic’s The Loom, Laidre was less convinced by the team’s conclusions. “There’s just zero evidence” to support the idea that the narwhal tusk is a sensory structure, she said. Heart rate fluctuations might instead reflect the stress response of the animals to being captured, she explained.