Danish researchers trace narwhal tusk’s spiral to inner structure

Danish researchers may have found why the narwhal’s long tusk grows straight while twisting around its own axis, DR reports. The findings come from an international study published in Nature Communications.

A research team led by Aarhus University spent six years examining a narwhal tusk from Greenland. Using advanced three dimensional X ray scans, the researchers examined the tusk’s molecular building blocks.

The results indicate that the tusk’s internal structure makes it grow both straight and in a spiral. It consists of several layers in which collagen fibres are arranged in specific directions, together forming a spiral pattern.

“By combining several different experiments, we have been able to piece together a picture of how the orientation of the collagen fibrils inside the tusk is connected to its overall spiral structure,” Henrik Birkedal, a professor at Aarhus University’s Department of Chemistry, told P1 Morgen.

The narwhal’s tusk is a tooth, although it differs from human teeth. It does not have the enamel outer layer found on human teeth.

The researchers travelled to international research facilities to carry out the work. They were typically given only a few days to use the advanced equipment, which could require them to work around the clock. The project was also delayed by the coronavirus pandemic.

The reason narwhals have the tusk remains unclear. The leading theory is that it serves a social purpose, possibly helping males display their fitness to females. Some researchers have also suggested that it could play a role in hunting, but the team currently considers its importance to narwhals’ social lives more likely.

Most narwhals with the characteristic tusk are males, although some females also develop one. The tusk can grow several metres long and weigh up to 14 kilograms. A few narwhals develop two tusks.

The researchers also hope to use the tusk’s annual ring like structures to learn more about the animal’s life, including how quickly it grew.