The narwhal tusk is a true oddity in the natural world.\u00a0<\/p>\n
Reaching up to three metres in length, the tusk is an upper tooth that grows through the whale's lip on the left side. And it is the only mammal tusk that grows perfectly straight, with no curves.<\/p>\n
A team of international researchers believe they have figured out why it grows so straight \u2014 and the answer lies in its unique pattern of opposing spirals.<\/p>\n
\u201cThis was really the first time that we could prove that this was the case and that there were two opposing spirals \u2026 that was really quite surprising to us,\u201d said study author Henrik Birkedal from Aarhus University in Denmark.<\/p>\n
New research published in the journal Nature Communications breaks down how the two opposing spirals \u2014 one going right, the other going left \u2014 allow the tusk to grow straight.<\/p>\n
The project began when Birkedal was approached by an organic chemistry colleague who was looking at why some molecules are right-handed and some left-handed.\u00a0<\/p>\n
The colleague had been visiting Greenland and heard that narwhal tusk spirals all go in the same direction, to the left. Birkedal decided to look into it.<\/p>\n
Birkedal\u2019s team collaborated with biologists from Greenland and physicists from Sweden to better understand the molecular structure of the tusks and spirals.<\/p>\n
\u201cWe really set out to try and understand how the spiralling tusk is related to the underlying structure of the tusk,\u201d he said.<\/p>\n
The tusks, which are mostly found on male narwhals, are made of dentine and cementum, similar to human teeth but without the hard layer of enamel.<\/p>\n
Through advanced imaging techniques that Birkedal described as being similar to CT scans, the researchers found two opposing spirals \u2014 a left-handed spiral on the outer layer of cementum, and a right-handed one in the inner layer of dentine.<\/p>\n
It's an important discovery, not just in solving the mystery of the narwhal's straight tusk but for its potential to help shed light on the structural principles of human bones on other similar instances, Birkedal said.<\/p>\n
Martin Nweeia, a narwhal biologist and specialist in marine mammal teeth at Harvard University, said he was delighted to see the research's deep-dive into what he calls "the most extraordinary tooth on the planet."<\/p>\n
\u201cNaturally, when a curious dentist meets the most extraordinary tooth, there's an irresistible urge to figure out what's going on here,\u201d he told CBC News.<\/p>\n
However, Nweeia \u2014 who was not associated with this study \u2014 said he was surprised to see the researchers characterize the tusk\u2019s function as \u201cspeculative\u201d in the initial pages of the paper.<\/p>\n