All narwhals have two teeth in their upper jaw. After the first year of a male narwhal's life, its left tooth grows outward, spirally. This long, single tooth projects from its upper jaw and can grow to be 7-10 feet (2-3 m) long. Tusks are usually twisted in a counterclockwise direction and have a hollow interior. The tusk's function is uncertain, perhaps used as a formidable jousting weapon in courtship and dominance rivalry, in obtaining food, and/or for channeling and amplifying sonar pulses (which they emit). The tusk is not used in hunting. Long ago, narwhal sightings reinforced (or started) the unicorn legends.
Narwhals can grow to be about 16 feet (4.9 m) long (not counting the tooth), and weigh about 1.8 tons (1.6 tonnes). Females are slightly smaller, averaging about 13 feet (4 m) long, and weighing 1 ton (0.9 tonnes). At birth, narwhals are about 5 feet (1.5 m) long and 175 pounds (80 kg).
Narwhal means "corpse whale" in Old Norse; this is perhaps a description of their skin, which is bluish-gray with white blotches (young narwhals are brown). Narwhals have a cylindrical body (with no dorsal fin) and a round head with a small mouth on their blunt snout. This compact body shape plus a thick layer of blubber retains heat in the icy Arctic waters in which they live.
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