Narwhals are a mighty impressive animal to look at - that incredible tusk could certainly do more than just poke your eye out. But what is its purpose? Researchers have long pondered this, with numerous ideas surfacing. It has been proposed to act as a swimming rudder, thermal regulator, a tool for breaking ice, a weapon, a breathing organ, and a hunting tool, amongst other things. That's quite an impressive list. But in a study published in the journal Anatomical Record, scientists have discovered that it actually provides a sensory function.
Narwhals, or narwhales, are toothed-whales in the same family as the beluga whale. They can be recognized by their characteristic long helical tusk, which is actually an elongated tooth. They are found in very cold locations; predominantly the Canadian Arctic and Greenlandic waters. Astonishingly, these tusks have been recorded to be as long as 3 meters, but they are hollow and therefore not particularly heavy. Some males even have two tusks, whereas only a small percentage of females display a tusk at all. This has led to the belief that it may act as a sexual characteristic.
Dr Martin Nweeia and his team started by analyzing the tusk itself, and they found that the outer layer of the tusk is in fact porous. The tusk has tubes which connect to and communicate with open channels through these pores. This allows the middle of the tusk, the pulp, to react to external stimuli with nerve endings which transmit information to the brain. The animal can sense chemical and temperature changes in the ocean environment through its tusk. Next, the team investigated the physiologic response of the narwhal task to changes in environmental stimuli. They found that the heart rate of the narwhal significantly changed when the tusk was exposed to solutions of alternating salt concentrations.
It is thought that this sensory ability may provide a mechanism whereby males can seek out females to reproduce with, and detect whether they are indeed ready for mating. Of course, it is difficult to rule out other suggestions for the role this tusk may play; the most likely scenario is that it has more than one purpose. What still remains unclear, however, is whether these sensory abilities have been evolving in the tusk over time, or whether they are actually slowly losing the ability to sense with their tusks.
Dr. Nweeia is now intending to gain information through observational studies of these animals in the wild, in the hope that it may shed more light on the roles these impressive tusks play.