Scientists Find 2nd Twist in 9-Foot Narwhal Tusks, Explaining Straight Growth

Q: What ancient Arctic climate secrets are locked inside the microscopic, tree-ring-like layers of this real-life unicorn horn?

The microscopic annual layers in narwhal tusks appear to preserve a long-term archive of Arctic environmental change — potentially recording shifts in ocean temperature, salinity, chemistry, sea-ice conditions and the whale’s own life history. Researchers say the tusk grows in bands much like tree rings, and those growth layers show distinct mineral and crystallographic signatures. Because narwhals can live for decades, sometimes up to about 80 years, a single tusk may hold a year-by-year record of the conditions the animal experienced across much of its life in the Arctic. That matters because narwhals are difficult to study directly in the high Arctic. If scientists can decode the chemical and structural differences from one layer to the next, the tusk could reveal when a whale encountered different water masses, changing feeding grounds or broader environmental shifts in the North Atlantic and Arctic. Related work already uses trace-element cycles in tusks to estimate age and map life history. The new structural study does not itself reconstruct past climate, but it strengthens the case that tusks are reliable archives by showing the annual bands are real, measurable and preserved within a stable, genetically programmed double-spiral architecture. Researchers now say they are working to determine whether those tree-ring-like layers can be used to track rapidly changing Arctic conditions over a narwhal’s lifetime.

3 articles · Updated · The New York Times · Aug 28

X-ray scans revealed a second, internal twist inside narwhal tusks, a structure researchers say may explain how the famously spiraled teeth grow straight instead of curving.
Nature Communications published the study after researchers used multiple X-ray systems, including a synchrotron in France measuring about 2,800 feet, to map the tusks’ inner architecture.
Narwhal tusks are elongated left canine teeth that can exceed 9 feet and usually appear in males, though females sometimes grow them and rare animals develop two tusks.
The tusk’s growth also reshapes the skull, with bones contorting to keep it relatively centered on the head and help preserve symmetrical swimming.