Scientists have cracked the code behind the narwhal's unique tusk, the only straight tusk in the animal kingdom. An international team of researchers has discovered how the spiralled yet arrow-straight tusks of male narwhals grow, solving a long-standing mystery. The tusk, a single tooth that can reach up to three meters long, has fascinated researchers for centuries due to its peculiar structure and the elusive nature of narwhals, which spend most of their lives under Arctic ice.
The study, published in Nature Communications, reveals that the tusks are composed of two types of dental tissue: dentin on the inside and cementum on the outside. Advanced 3D X-ray technology, including three European synchrotrons, showed that the inner dentin forms a right-handed spiral while the outer cementum forms a left-handed spiral. These counter-acting forces result in the tusk's straight structure, unlike the curved tusks of other animals such as elephants.
Henrik Birkedal, a chemist at Aarhus University in Denmark and the senior author of the study, likened the sensation of carrying such a tusk to "riding on a bicycle with a broom strapped to your head." Despite this cumbersome appendage, male narwhals navigate their underwater world with apparent ease.
The research team, comprising biologists, chemists, and physicists, also found growth layers within the tusks similar to tree rings, providing insights into the narwhals' lifespan, which can extend up to 80 years. The study utilized tusks from museums and those collected by Greenland's indigenous Inuit people, who hunt narwhals for food.
While the study sheds light on the tusk's growth mechanism, the exact purpose of the tusk remains debated. Some scientists hypothesize that tusks are used for hunting or sensing water conditions, while others suggest they play a role in establishing dominance and attracting mates. Mads-Peter Heide Jorgensen of the Greenland Institute of Natural Resources believes the latter is more likely, citing observations of male narwhals engaging in tusk-measuring contests.
However, Martin Nweeia, a leading narwhal tusk expert from Harvard University, disagrees, arguing that the primary function of the tusk is as a sensory organ system. Despite this disagreement, Nweeia praised the study for its valuable contributions to understanding tusk micro-anatomy and morphology.
This discovery not only enhances our understanding of narwhal biology but also highlights the importance of international collaboration in scientific research. For Bangladesh, where marine biodiversity is a critical component of ecological balance, such studies underscore the value of protecting and studying unique species, even those far from its shores.
