How a narwhal’s 10-foot tooth stays straight has puzzled scientists for years

An international team of biologists, chemists and physicists has used sophisticated 3D X-ray technology to investigate the tooth at an unprecedented level.

A unicorn may be a mythical creature, but nature made something very similar under the Arctic ice. Wondering what? Well, the narwhal has a strange tusk that can reach nearly 10 feet long from the animal’s head, erupting from its upper lip in a bizarre display that has intrigued people for centuries. Now, scientists have worked out a molecular explanation for one of its oddest features: how a tusk that twists as it grows can remain surprisingly straight. According to a study published by Phys Org, narwhals have one prominent tusk, usually found in males. The fact is that it is a canine tooth that grows through the jaw and upper lip and the corresponding right canine usually remains embedded inside the head. The tusk may grow to a length of some three meters (10 feet). Its unusual appearance helped fuel legends of unicorns during the Middle Ages, and narwhal tusks were sometimes sold as magical unicorn horns. But for today's scientists, the tusk is a very real challenge in research. Narwhals live much of their lives in the Arctic, often beneath sea ice, making them elusive animals to see and study. Scroll down to read the details of this nature's magic.

The “Narwhal Tusk Puzzle” solved

An international team of biologists, chemists and physicists has used sophisticated 3D X-ray technology to investigate the tooth at an unprecedented level, states the online report.

Researchers studied tusks at three European particle accelerators, called synchrotrons. These facilities produce very intense X - rays that enable scientists to probe the inside of materials at microscopic and molecular scales. Their results were published in Nature Communications and it was found that the tusk is comprised of two main types of dental tissue: dentin on the inside and cementum on the outside. Interestingly the two tissues form spirals in opposite directions. The inner dentin is a right-handed spiral, the outer cementum is a left-handed spiral. “The opposing structures balance each other well, helping to create the unusual combination of spiral texture and straight form of the tusk,” senior author Henrik Birkedal of Aarhus University said in a statement. He likened the mechanism to a screw passing through wood, except that in the case of the narwhal, the “screw” is emerging from the animal’s head.

A record of a lifetime tooth

The researchers also found something unexpected inside the tusks: growth layers that resemble tree rings. These layers could give scientists clues about a narwhal’s life and possibly help piece together parts of its history. Narwhals can live for decades, with some thought to reach an age of about 80 years, so the tusk could be a valuable biological record. The study looked at tusks and specimens collected by Indigenous Inuit peoples in Greenland, where narwhals are hunted for food, and held in museums.

But what use is a big tusk?

As per experts, understanding the growth of the tusk doesn’t fully answer the bigger question: what is it for? Scientists have suggested various theories, including hunting, detecting changes in water temperature and salinity and social interaction. The authors of the new study say that hunting or sensory functions seem less convincing because tusks are overwhelmingly found in males. According to Mads-Peter Heide Jorgensen, a researcher at the Greenland Institute of Natural Resources, if the tusk is important for those things, why wouldn’t we expect females to have them too? Observations of male narwhals apparently comparing or crossing tusks in front of females have bolstered the idea that the structure has a role in competition, dominance or attracting mates.

The mystery that remains unsolved

Not all are convinced. Martin Nweeia, a leading narwhal tusk researcher at Harvard who was not involved in the study, said his earlier work suggests the primary function of the tusk is a sensory organ system. The new research, then, fills in an important piece of the puzzle, even if the researchers disagree. Scientists have revealed the microscopic architecture that keeps the narwhal's extraordinary tooth straight, showing that one of nature's strangest structures is also one of its most ingeniously engineered.Images Courtesy: istock