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Why does a narwhal’s tusk twist and what’s it made of?
An international research team led by chemist Henrik Birkedal of Aarhus University in Denmark published findings in Nature Communications revealing that narwhal tusks possess a double-helix structure of mineralized collagen providing exceptional strength.
Despite growing over 6.6 feet long, narwhal tusk formation eluded scientists for decades; researchers previously understood the left-handed spiral shape but lacked knowledge of the interior molecular structure at atomic scales.
Using particle accelerator X-ray sources at synchrotrons in Sweden, Switzerland, and France, the team mapped the tusk's interior, discovering the outer cementum layer forms a left-handed helix while the inner dentine layer forms a right-handed helix.
The opposing double-helix structure makes tusks more stable against bending and twisting than single-spiral designs, with flexible fibers and stiff mineral matrix working together—insights that could help materials scientists design advanced materials for construction and medicine.
Birkedal said researchers are working to analyze annual growth layer patterns to "map the life history of a narwhal through its tusk and thereby gain insights into living conditions for the whales in the arctic." Since narwhals live up to 80 years, their tusks form a historical record.