A multinational team of scientists has uncovered the secret behind the narwhal’s twisted tusk using advanced X-ray technology, revealing a double-spiral structure that combines left-handed and right-handed collagen fibrils. The discovery, published in Nature Communications, sheds light on the tooth’s extraordinary mechanical properties and its potential applications in materials science.
The Double-Spiral Discovery
Researchers from Aarhus University in Denmark, collaborating with institutions like the Greenland Institute of Natural Resources and synchrotron facilities in Sweden, Switzerland, and France, found that the narwhal’s tusk contains two opposing spirals. The outer layer, composed of cementum, forms a left-handed spiral, while the inner dentin layer creates a right-handed spiral.
The team used tensor tomography, a 3D X-ray technique, to map the tusk’s internal structure at the nanoscale. This method, which required access to three major synchrotrons—MAX IV, the Swiss Light Source, and the European Synchrotron Radiation Facility (ESRF)—revealed how mineralized collagen fibrils are arranged. The findings, published in Nature Communications, show that the double-spiral architecture is preserved across the tusk’s annual growth layers, suggesting a genetically programmed design that remains stable throughout the narwhal’s lifespan, which can extend to approximately 80 years.
Technological Breakthroughs
The study’s success hinged on overcoming the tusk’s complexity. Unlike human teeth, it has no enamel but consists of dentin on the inside and cementum on the outside. Its length—can reach more than two meters—and intricate spiral structure demanded the most powerful imaging tools available. By combining X-ray computed tomography, scanning small-angle X-ray scattering, and tensor tomography, the researchers achieved unprecedented resolution.
The team also conducted mechanical tests, including three-point bending experiments, to confirm the tusk’s strength. The results showed that the double-spiral design makes it more resistant to bending and twisting than a single spiral or a straight rod. This natural engineering marvel, the researchers noted, could inspire new composite materials for construction and medicine.
It also provides new insight into how nature constructs advanced materials with extreme mechanical properties.
Biological Implications
While the tusk’s exact function remains debated, the study clarifies its structural advantages. Most experts believe it serves as a sexual signal, as males typically develop tusks, though some females do as well. However, marine biologists in Greenland have found no evidence that the tusk detects environmental changes like temperature or salinity, as previously hypothesized.
The double-spiral structure, however, may explain why the tusk grows straight, unlike, say, an elephant’s curved tusk. This consistency suggests a deep evolutionary adaptation, though the exact purpose of the tusk remains unclear.
The discovery not only solves a centuries-old natural science mystery about one of the ocean’s most iconic animals. It also provides new insight into how nature constructs advanced materials with extreme mechanical properties—knowledge that could inspire new composite materials for fields such as construction and medicine.
Future Research Directions
The team is now exploring whether the tusk’s structure can serve as a historical record of environmental changes in the North Atlantic. Because whales can live for up to 80 years, their teeth may preserve data about ocean conditions over decades. This could help scientists track climate change impacts on Arctic ecosystems.
Further research will also examine the microstructure of the cementum layer, which features radial collagen fiber bundles. Co-author Henrik Birkedal noted that the team plans to study these finer details using micro- and nano-beam experiments.
The study’s interdisciplinary approach—uniting materials science, biology, and physics—highlights the value of collaboration in solving complex natural mysteries. As Rodriguez-Palomo put it, We have only been able to do it by collaborating across several disciplines—namely chemistry, physics, materials science, and biology.
