Researchers from Aarhus University and partners in Sweden, Switzerland and France have solved a long‑standing mystery about the narwhal’s iconic tusk. By employing state‑of‑the‑art three‑dimensional X‑ray tomography, they mapped the interior of the tooth in unprecedented detail.
Double‑spiral architecture
The study, published in Nature Communications, shows that the tusk is not a single helix but a “double‑spiral” structure. The outer cementum forms a left‑handed spiral, while the inner dentin forms a right‑handed spiral. These opposing spirals meet at the transition between the two materials, creating a biological counterbalance that enhances resistance to bending and twisting.
How the research was done
Scientists combined several X‑ray imaging methods, most notably tensor tomography, which sends powerful X‑rays through the tooth and analyzes how they scatter from nanoscale mineralized collagen fibrils. To achieve the necessary resolution, they used three of the world’s largest synchrotron facilities: MAX IV in Sweden, the Swiss Light Source, and the European Synchrotron Radiation Facility in France.
Implications for biology and engineering
The double‑spiral design provides the tusk with superior mechanical properties, making it far more stable than a straight rod or a single‑spiral structure. This architecture is also found in other natural materials that must endure large forces, suggesting potential inspiration for new composite materials in construction and medicine.
What the tusk might tell us
Beyond its strength, the tusk records annual growth layers, much like tree rings, offering a historical record of the animal’s environment over a lifespan that can reach 80 years. Researchers are now investigating whether these records can reveal changes in the rapidly warming North Atlantic.
Future directions
Lead author Adrian Rodriguez‑Palomo emphasized the interdisciplinary nature of the work, noting that collaboration among chemists, physicists, materials scientists and biologists was essential. Project leader Henrik Birkedal added that the team plans to explore how the tusk’s growth patterns may reflect long‑term climate shifts, providing a novel tool for Arctic research.
Original reporting: KTBS 3 (Shreveport) — read the source article.
