Why does a narwhal's tusk twist and what's it made of?

Key Points:

• Researchers have uncovered the narwhal tusk's unique double-spiral structure using advanced 3D X-ray tensor tomography, revealing an outer left-handed spiral and an inner right-handed spiral that create a biological counterbalance.
• The tusk, which is actually the whale's left canine tooth, lacks enamel and consists of dentin inside and cementum outside; this double-spiral design enhances its mechanical stability against bending and twisting.
• While the exact function of the tusk remains uncertain, it is widely believed to serve as a sexual signal primarily in males, though some hypotheses suggest sensory roles that have yet to be confirmed by behavioral evidence.
• The study, involving collaboration across chemistry, physics, materials science, and biology, utilized powerful synchrotron X-ray facilities in Sweden, Switzerland, and France to map the tusk's internal structure in unprecedented detail.
• Findings not only solve a long-standing natural mystery but also offer insights into advanced natural materials, potentially inspiring new composite designs for construction and medical applications, with ongoing research exploring environmental records preserved in the tusk.