This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Narwhals have nature's only straight tusk, a single tooth up to three meters (10 feet) long, so strange they were sold as magical unicorn horns during the Middle Ages. The tusks have fascinated scientists ever since, but they have proven extremely difficult to study because these odd-looking, blubbery whales spend most of their lives under the Arctic ice.
But on Tuesday, a large international team of researchers announced they had solved a long-running mystery about the tusks: how they get their uniquely spiraled yet arrow-straight form. The left canine tooth of male narwhals grows through the jaw and upper lip, jutting out into the animal kingdom's only single tusk. The right canine stays buried in the head.
"Imagine that you had to ride on a bicycle with a broom strapped to your head," said Henrik Birkedal, the senior author of a study in Nature Communications describing the new discovery. That is how it must feel for male narwhals to dive deep underwater, the chemist at Aarhus University in Denmark told AFP. Yet despite this huge "Monty Pythonesque" protuberance, the animals seem to get about just fine, he added.
To solve what they called the "narwhal tusk puzzle," the team of biologists, chemists and physicists used advanced 3D X-ray technology, including three European particle accelerators called synchrotrons. The tusks are made of two kinds of dental tissue: dentin on the inside and cementum on the outside. At a molecular level, the inner dentin forms a right-handed spiral while the outer cementum forms a left-handed spiral, the powerful X-ray scans revealed.
These two counteracting forces give the tusks the straight structure that is so different from the curved tusks of other animals, such as elephants. "Imagine you turn a screw into a piece of wood, and with each turn, the screw penetrates deeper," Birkedal explained. Narwhal tusks are similar—except the screw is pushing farther out from the animal's head.
The scientists were also surprised to find growth layers similar to tree rings inside the tusks, which offer a glimpse into their lives, which can last up to 80 years. To conduct the research, they used tusks from museums as well as those collected by Greenland's Indigenous Inuit people, who hunt narwhals for food. This was not the only lingering mystery about narwhal tusks.
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