A new study published in Nature Communications reveals that the narwhal's famous spiral tusk contains a second internal spiral running in the opposite direction to its visible left-handed twist, offering fresh insight into the structure long shrouded in myth and mystery. The tusk, actually an elongated canine tooth that erupts from the upper left jaw of male narwhals, has fascinated scientists for its unusual growth pattern and possible functions, from sensing changes in water temperature and salinity to stunning prey or serving as a status symbol shaped by sexual selection.

Researchers scanned two male narwhal tusk and skull specimens using a combination of X-ray computed tomography, scanning X-ray diffraction, small-angle X-ray scattering, tensor tomography and birefringence microscopy, work that required time on three large synchrotron facilities in Sweden and Switzerland. This allowed them, for the first time, to map the tusk's internal structure across atomic, nano and macro scales, showing that the arrangement of mineralised collagen fibrils forms a double-helix-like pattern rather than a single uniform spiral, which helps explain both the tusk's shape and its material properties.