Within the Center Ages, narwhal tusks have been bought as unicorn horns blessed with magical powers comparable to neutralizing poisons and curing illnesses — prized possessions of monarchs and nobles price greater than their weight in gold. They supplied no such powers, in fact, however even at this time stay objects of thriller.
Researchers have now deciphered the interior construction of those spiral-shaped tusks — really a straight and elongated canine tooth that protrudes from a narwhal’s mouth, typically reaching as much as 10 toes (3 meters) lengthy. Utilizing superior three-dimensional X-ray imaging, they discovered that whereas the outside of the tusk, product of dental tissue known as cementum, shows a left-handed spiral, its inside, product of dental tissue known as dentine, reveals a right-handed spiral.
“We suggest that this association helps the tusk develop straight, in contrast to different tusks — elephant or walrus, for instance — that curve,” stated supplies chemist Henrik Birkedal of Aarhus College in Denmark, who helped lead the research printed this week within the journal Nature Communications.
The overwhelming majority of male narwhals and a small share of feminine narwhals have considered one of these tusks — a couple of males even have two of them — although their function stays unclear.
“The tusk could have a number of capabilities. The tusks appear to perform to determine social hierarchy amongst males, and is thus a sexually chosen trait used throughout male-male contests. It has additionally been proposed that the tusk could serve in play and as a sensory organ,” Birkedal stated.
A Case of Organic Counterbalance
Narwhals, which may attain round 17 toes (5 meters) lengthy, inhabit the frigid waters of the Arctic Ocean, primarily close to Canada, Greenland, Norway and Russia, and feed on fish, squid and shrimp. Their colour adjustments with age; they’re born with a blue-gray hue that turns blue-black of their juvenile years and mottled grey in maturity, solely to turn out to be almost all white in outdated age.
The researchers discovered that the large-scale helical construction of the tusk arises from preparations of mineralized collagen — an necessary protein in bones, enamel and pores and skin — at a microscopic stage in fibers known as fibrils.
“The fibrils are sturdy and versatile. Within the narwhal tusk, and in our enamel and bones, the collagen fibrils are strengthened by nanoparticles of a calcium-mineral to make a powerful so-called composite materials,” Birkedal stated.
“The collagen fibrils are aligned virtually parallel to the lengthy axis of the tusk. Nevertheless, they deviate systematically to type two helical patterns, one in cementum and one other in dentine, with reverse handedness,” Birkedal added.
This double-spiral construction produces a organic counterbalance through which two opposing forces meet on the level of contact between inside and exterior components, giving the tusk useful mechanical properties for stability in opposition to bending and twisting — superior to a single spiral or a straight rod.
“We expect this will likely act as a supply of inspiration for design of bioinspired supplies,” Birkedal stated.
A world staff of biologists, chemists and physicists carried out the analysis utilizing superior X-ray expertise, together with three European synchrotron particle accelerators. The tusks examined got here from museum collections in addition to specimens collected by Inuit hunters in Greenland, who hunt narwhals for meat.
The scientists additionally found development layers contained in the tusks, just like tree rings, which give clues concerning the life historical past of narwhals, a species that may dwell as much as 80 years.
The Goal Debate Continues
Whereas the structural thriller of how the tusk maintains its straight type seems resolved, the query of what the tusk is definitely for stays contested.
Some researchers have proposed that narwhals use their tusks to hunt prey or to sense temperature and salinity within the water. Nevertheless, the research authors contemplate these capabilities unlikely as a result of tusks develop virtually completely in males. If the tusk served these functions, females would presumably want them too.
Researchers have noticed two males apparently “crossing tusks” in entrance of a feminine, suggesting the tusks could also be used to determine dominance and impress potential mates.
“That is actually the most certainly use of the tusk,” stated Mads-Peter Heide Jorgensen, a research co-author from the Greenland Institute of Pure Sources.
However Martin Nweeia, a number one narwhal tusk knowledgeable from Harvard College who was not concerned within the new analysis, disagreed. He maintains that “the first perform of this tusk is a sensory organ system,” citing his personal earlier research. Regardless of the disagreement, Nweeia stated the brand new analysis stays a precious contribution to scientific understanding of narwhal tusks.
From Unicorn Horns to Royal Thrones
Whereas unicorns and the magical properties of narwhal tusks have been mere legend, they have been widespread beliefs centuries in the past.
“The primary scientific depictions are from the mid-1500s the place a Swedish cartographer drew the narwhal like a fish-like creature with a horn,” Birkedal stated.
Within the 1600s, Birkedal added, “The Danish pure historian Ole Worm concluded that narwhal and unicorn tusk powders have been one and the identical, and described skulls of marine unicorns that resemble narwhals.”
The Coronation Chair of Denmark that was used within the coronations of Danish monarchs from 1671 to 1840, commissioned by King Frederik III and now displayed at Rosenborg Fort in Copenhagen, was product of narwhal tusks.
“The tusks thus carried nice status,” Birkedal stated.
For the narwhals themselves, the double-spiral structure represents a chic evolutionary resolution to a mechanical problem. As Birkedal put it: “Think about it’s important to experience a bicycle with a brush tied to your head.” That, he recommended, is what male narwhals expertise when diving deep underwater — but their tusks stay arrow-straight because of the opposing helical forces locked inside.
