Narwhal

The tusk is often said to hold ten million nerve endings. The research behind that describes something else: tiny channels running from the surface toward nerves in the pulp. Whether that makes it a sense organ is disputed, and most females, which rear the calves, grow no tusk at all.

The tusk is a tooth, the upper left canine, grown straight out through the lip and spiralling as it goes, up to about 3 metres long. A few males grow two.

The strongest evidence for what it is really for points to rivalry. A 2020 study of 245 males found that tusk length grows out of proportion to body size, the pattern expected of a trait shaped by sexual selection, like a stag's antlers. Males are seen crossing tusks at the surface, a behaviour called tusking.

In winter, narwhals dive beyond 1,500 metres under the Baffin Bay pack ice to feed on Greenland halibut, and a single dive can last up to about 25 minutes.

Least Concern globally, with about 170,000 animals, most of them in Baffin Bay. The picture is not the same everywhere: the small East Greenland stocks are depleted and declining, and the NAMMCO Scientific Committee has recommended ending the hunt there since 2019.

Narwhals can live a long time. A study reading the chemistry of the eye lens put one wild female at around 115 years, though the estimate carries a wide margin.

This one was photographed from the air off Franz Josef Land in the Russian Arctic, in July 2021.