Here's the abstract from the publication Sensory ability in the narwhal tooth organ system:
ABSTRACT
The erupted tusk of the narwhal exhibits sensory ability. The hypothesized sensory pathway begins with ocean water entering through cementum channels to a network of patent dentinal tubules extending from the dentinocementum junction to the inner pulpal wall. Circumpulpal sensory structures then signal pulpal nerves terminating near the base of the tusk. The maxillary division of the fifth cranial nerve then transmits this sensory information to the brain. This sensory pathway was first described in published results of patent dentinal tubules, and evidence from dissection of tusk nerve connection via the maxillary division of the fifth cranial nerve to the brain. New evidence presented here indicates that the patent dentinal tubules communicate with open channels through a porous cementum from the ocean environment. The ability of pulpal tissue to react to external stimuli is supported by immunohistochemical detection of neuronal markers in the pulp and gene expression of pulpal sensory nerve tissue. Final confirmation of sensory ability is demonstrated by significant changes in heart rate when alternating solutions of high-salt and fresh water are exposed to the external tusk surface. Additional supporting information for function includes new observations of dentinal tubule networks evident in unerupted tusks, female erupted tusks, and vestigial teeth. New findings of sexual foraging divergence documented by stable isotope and fatty acid results add to the discussion of the functional significance of the narwhal tusk. The combined evidence suggests multiple tusk functions may have driven the tooth organ system's evolutionary development and persistence. Anat Rec, 297:599–617, 2014. © 2014 Wiley Periodicals, Inc.
However, note the underlined text above (
my emphasis). As reported by the
National Geographic's article on this research, there is some healthy controversy about this aspect of the research:
The scientists speculate that the tusk, usually found only the males, can pick up differences in the whale's environment, like the salt content of seawater, helping the marine mammals to navigate their frigid homes or perhaps find food.
But the theory is highly controversial; many marine mammal experts reject the idea that the tusk plays a central role in a narwal's ability to sense its environment, insisting that the tooth is most likely a lure to attract mates.
"There's just zero evidence" for the possibility that a male narwhal's tusk plays a large role in whether the animal can sense things like changes in salinity or where to find food, says Kristin Laidre, a marine mammal biologist at the University of Washington in Seattle.
<snip>
But the University of Washington's Laidre notes that researchers collected those heart rate measurements shortly after the whales were captured in nets and brought into shallow water. A heart rate obtained shortly after an invasive capture reflects the animal's stress, she says, not necessarily its reaction to a change in salinity.
It is always inspiring to observe the scientific process in action. Publish, propose, and debate. A perfect example of Neil deGrass Tyson's quote about the science from last Sunday's Cosmos, in Science there is no shame in being wrong:
"The only shame is to pretend we have all the answers."
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