Narwhal (Monodon monoceros)—Painting by Richard Ellis
Toothed whale (Monodon monoceros, family Monodontidae) of the Arctic, found in groups of 15–20 along coasts and sometimes in rivers. Narwhals are mottled gray, attain a length of 11.5–16 ft (3.5–5 m), and have no dorsal fin. They have only two teeth, at the upper jaw tip. The male's left tooth is a straight, protruding tusk, up to 8.9 ft (2.7 m) long, that is grooved on the surface in a left-handed spiral. It was prized in medieval times as the unicorn horn. The tusk is thought to have evolved as a sexual display. Narwhals eat fishes, cephalopods, and crustaceans. They are hunted by humans for their tusks and meat.