Narwhal tusks exhibit a complex spiral structure that extends beyond their well-known external twist, new research reveals. Scientists using X-ray imaging have discovered that beneath the tusk’s distinctive leftward spiral lies a second, internal twist that winds in the opposite direction. This dual twisting pattern may help explain how narwhal tusks maintain their remarkable straightness despite their length and aquatic environment.

The narwhal’s tusk, a specialized tooth that can exceed nine feet in length, grows through the animal’s upper lip and is predominantly seen in males, though females occasionally develop the feature as well. Rarely, narwhals may have two tusks, with both the left and right canines protruding. As the tusk grows, it also influences the shape of the whale’s skull, causing deformities as the bones adjust to accommodate and center the tusk on the head. This structural adaptation is believed to contribute to more balanced swimming.

Using X-ray scans of tusk fragments, researchers observed that the outer layer of the tusk twists consistently in one direction while an internal layer twists oppositely. The scientists noted that this pattern was evident at multiple scales within the tusk, similar to the grain patterns found in timber. They theorize that these opposing twists provide mechanical strength, enabling the tusk to withstand intense underwater pressure and maintain its linear form.

Marianne Liebi, a physicist at Chalmers University of Technology and co-author of the study, highlighted the observable changes in the whale’s skull as the tusk develops, emphasizing the biological adaptation involved. Henrik Birkedal, a chemist at Aarhus University and also part of the research team, expressed surprise at the discovery, describing their reaction to the findings as “flabbergasted.”

This new insight into the unique structure of narwhal tusks adds to the understanding of how these distinctive marine mammals adapt to their environment and develop such striking features.