Narwhal Tusk's Opposing Spirals Revealed in New Study

On August 18, a study featured in Nature Communications revealed the structural intricacies of the narwhal's distinctive straight, spiral tusk. Led by Henrik Birkedal, a chemist from Aarhus University in Denmark, the research identified two layers within the tusk: an outer cementum layer and an inner dentine layer, which spiral in opposite directions. The cementum forms a left-handed helix, while the dentine twists in a right-handed manner. This unique configuration contributes to the tusk's straight growth and resilience against bending and twisting, outperforming a single-spiraled rod. The study utilized tusks from Greenlandic Inuit hunters and the Greenland Institute of Natural Resources, employing advanced microscopy, X-rays, and CT scans. Martin Nweeia, a narwhal specialist and dentist at Harvard University, described the tusk as "the most extraordinary tooth on the planet." The findings indicate a more intricate boundary between cementum and dentine than previously understood. Additionally, the research noted the opposing spiral structure in annual growth layers, akin to tree rings, which may aid in mapping narwhal life histories. Future investigations will focus on the patterns of annual growth layers and the tusk's development within the skull.