Scientists scanned narwhal tusks with X-rays and found two spirals twisting in opposite directions \u2013 a design no one expected to see.<\/p>\n
A male narwhal grows one tooth into a corkscrew that pushes straight through its upper lip. The tooth keeps twisting in the same direction throughout the animal\u2019s life. <\/p>\n
Split that tooth down the middle, and the two halves spring apart on their own, untwisting by more than half a turn.<\/p>\n
Something inside the tooth holds considerable strain. Until now, nobody knew what it was.<\/p>\n
Henrik Birkedal, a chemist at Aarhus University<\/a> in Denmark, led the team that went looking for the source of that tension.<\/p>\n Working with colleagues in Sweden and France, his team scanned narwhal tusks<\/a> with powerful X-rays. The beams were precise enough to map how structures only a few hundred atoms across were arranged inside the tooth.<\/p>\n Narwhal tusks inspired unicorn myths<\/p>\n The tusk isn\u2019t a horn at all. It\u2019s a tooth: the left canine erupts through a male narwhal\u2019s upper lip and grows to more than 6 feet (2 meters) long. <\/p>\n The tusk keeps corkscrewing to the left for as long as the animal lives, which can be 80 years or more.<\/p>\n That slow spiral growth is unlike anything else in nature. In the 1600s, twisted white tusks arriving at European trading ports convinced buyers that they had found real unicorn<\/a> horns.<\/p>\n Denmark\u2019s King Frederik III believed the myth strongly enough to have an entire coronation throne made from them. The throne was completed in 1671.<\/p>\n Narwhals do plenty with that outsized tooth besides starting rumors. They use their tusks to stun small fish<\/a> before eating them. <\/p>\n Drone footage has also captured narwhals swatting and playing with their tusks the way another animal might use a paw.<\/p>\n Their long lives already come under other pressures. Narwhals have had to shift their migration patterns as Arctic sea ice<\/a> forms later each year.<\/p>\n X-rays searched inside the tusk<\/p>\n Birkedal\u2019s team suspected that whatever caused the twist would appear as a single spiral within the tooth\u2019s building blocks. <\/p>\n Those building blocks consist of collagen threads embedded with tiny mineral crystals, the same basic materials that make up bone.<\/p>\n Mechanical tests on cut tusks had already suggested that the spiral ran deep. Splitting a tusk lengthwise allowed pent-up stress to twist the two halves apart by more than half a turn and sometimes even farther.<\/p>\n The team aimed X-rays at thin tusk slices at synchrotron facilities in Switzerland and Sweden, as well as the European Synchrotron Radiation Facility in France.<\/p>\n The researchers rotated each slice point by point, building a 3D map of how the threads inside were arranged. The first scans produced a puzzling result.<\/p>\n \u201cThat puzzled us quite a bit,\u201d said Marianne Liebi, a physicist at the Paul Scherrer Institute in Switzerland and a co-author of the study. \u201cBut instead of a helix, all we saw was a regular pattern.\u201d<\/p>\n Two hidden spirals emerged<\/p>\n The key was to stop examining each measurement point on its own. Instead, the team compared every point with its neighbors.<\/p>\n \u201cWhen we compared how these points were oriented relative to each other, a directional trend began to appear,\u201d said Adrian Rodriguez-Palomo, the study\u2019s first author.<\/p>\n Rodriguez-Palomo worked on the project as a doctoral student at Chalmers University of Technology in Sweden. She later continued the research as a postdoctoral researcher at Aarhus University.<\/p>\n \u201cAll we had to do then was connect the dots \u2013 as in a children\u2019s paint-by-numbers kit \u2013 and suddenly the structure became visible: two intertwined spirals,\u201d she said.<\/p>\n The two spirals run in opposite directions. On the outside, a layer called cementum forms a left-handed spiral. Cementum is the material that usually caps a tooth\u2019s root, and its spiral is visible on the tusk\u2019s surface.<\/p>\n Beneath the cementum, within the tooth\u2019s main bulk of dentine, the collagen-and-mineral threads spiral in the opposite direction, to the right. Dentine is the same material found beneath the enamel<\/a> of a human tooth.<\/p>\n The two spirals meet and lock together where the cementum and dentine touch.<\/p>\n Collagen is a common tissue protein. It also preserves ancient dietary clues inside teeth that are thousands of years old, although it has never been found twisted into anything like this.<\/p>\n Double spiral makes the tusk stronger<\/p>\n The two intertwined spirals work like reinforcement embedded in concrete.<\/p>\n \u201cLike bones or other teeth in the animal kingdom, the narwhal tusk is a complex composite material whose structure extends from tiny nanoscale building blocks to the visible form of the entire tooth,\u201d said Liebi.<\/p>\n \u201cThe narwhal tusk, too, must be both hard and flexible. Only then can it withstand the strong hydrodynamic forces that swimming generates.\u201d<\/p>\n The researchers tested that toughness directly. They bent rod-shaped samples cut from the tusk in two directions: lengthwise and crosswise.<\/p>\n The rods cut along the tusk\u2019s length resisted bending about 63 percent more than those cut across it. They also held together much longer before failing.<\/p>\n Under a microscope, the crosswise rods snapped cleanly, much like a ceramic plate shattering. By contrast, the lengthwise rods tore apart slowly. Their fibers pulled loose and redirected the crack sideways as it spread.<\/p>\n That toughness helps the tusk survive years of drag as a narwhal repeatedly dives to feed.<\/p>\n The twist remains a mystery<\/p>\n Birkedal\u2019s team studied tusks from only two adult male narwhals. Both animals came from a Greenland population with surprisingly low genetic diversity for its size.<\/p>\n A larger sample could reveal whether every tusk develops its two spirals in the same way. It could also show whether rare double-tusked narwhals found in Greenland follow the same pattern.<\/p>\n No one has yet explained how a growing tooth begins spiraling in one direction on the outside and the opposite direction on the inside.<\/p>\n The researchers suspect that the answer lies at the boundary where the two tissues meet. Confirming that idea would require watching a tusk grow from the beginning. No one has yet managed that in a wild whale<\/a> that can live for 80 years.<\/p>\n For now, the discovery gives engineers a working design that nature has tested for millions of years.<\/p>\n Anyone building drill shafts or suspension cables that must resist twisting now has a natural blueprint, one old enough to have inspired a myth about unicorns.<\/p>\n The full study was published in the journal Nature Communications<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? Subscribe to our newsletter<\/a> for engaging articles, exclusive content, and the latest updates.\u00a0<\/p>\n Check us out on EarthSnap<\/a>, a free app brought to you by Eric Ralls<\/a> and Earth.com.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"Scientists scanned narwhal tusks with X-rays and found two spirals twisting in opposite directions \u2013 a design no…\n","protected":false},"author":2,"featured_media":597442,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[85,46,141,386],"class_list":["post-597441","post","type-post","status-publish","format-standard","has-post-thumbnail","category-wildlife","tag-il","tag-israel","tag-science","tag-wildlife"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/597441","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/comments?post=597441"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/597441\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media\/597442"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media?parent=597441"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/categories?post=597441"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/tags?post=597441"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}