Vikings sold Narwhal tusks during the middle ages, leading to the imaginative tales of unicorns in our fantasy books… and continued myths about the narwhal itself. What is a narwhal? And why do they have a large tusk? From Wikipedia:
The narwhal, or narwhale (Monodon monoceros), is a medium-sized toothed whale that possesses a large “tusk” from a protruding canine tooth. It lives year-round in the Arctic waters around Greenland, Canada, and Russia. It is one of two living species of whale in the Monodontidae family, along with the beluga whale. The narwhal males are distinguished by a long, straight, helical tusk, which is an elongated upper left canine. The narwhal was one of many species described by Carl Linnaeus in his publication Systema Naturae in 1758…
The tusk is an innervated sensory organ with millions of patent nerve endings connecting seawater stimuli in the external ocean environment with the brain. The rubbing of tusks together which males engage in is now hypothesized to communicate information about the water each has traveled through rather than to represent the previously assumed “male-to-male rivalry”. Narwhals have only occasionally been observed using the tusk for aggressive behavior.