<P> Narwhals are medium - sized whales, and are around the same size as beluga whales . Total length in both sexes, excluding the tusk of the male, can range from 3.95 to 5.5 m (13 to 18 ft). Males, at an average length of 4.1 m (13.5 ft), are slightly larger than females, with an average length of 3.5 m (11.5 ft). Typical adult body weight ranges from 800 to 1,600 kg (1,760 to 3,530 lb). Male narwhals attain sexual maturity at 11 to 13 years of age, when they are about 3.9 m (12.8 ft) long . Females become sexually mature at a younger age, between 5 and 8 years old, when they are around 3.4 m (11.2 ft) long . </P> <P> The pigmentation of narwhals is a mottled pattern, with blackish - brown markings over a white background . They are darkest when born and become whiter with age; white patches develop on the navel and genital slit at sexual maturity . Old males may be almost pure white . Narwhals do not have a dorsal fin, possibly an evolutionary adaptation to swimming easily under ice . Their neck vertebrae are jointed, like those of land mammals, instead of being fused together as in most whales . Both these characteristics are shared by the beluga whale . The tail flukes of female narwhals have front edges that are swept back, and those of males have front edges that are more concave and lack a sweep - back . This is thought to be an adaptation for reducing drag caused by the tusk . </P> <P> The most conspicuous characteristic of the male narwhal is a single long tusk, a canine tooth that projects from the left side of the upper jaw, through the lip, and forms a left - handed helix spiral . A tusk grows throughout life, reaching a length of about 1.5 to 3.1 m (4.9 to 10.2 ft). It is hollow and weighs around 10 kg (22 lb). About one in 500 males has two tusks, occurring when the right canine also grows out through the lip . Only about 15 percent of females grow a tusk which typically is smaller than a male tusk, with a less noticeable spiral . Collected in 1684, there is only one known case of a female growing a second tusk (image). </P> <P> The tusk is an innervated sensory organ with millions of nerve endings connecting seawater stimuli in the external ocean environment with the brain . The rubbing of tusks together by male narwhals is thought to be a method of communicating information about characteristics of the water each has traveled through, rather than the previously assumed posturing display of aggressive "male - to - male rivalry ". In August 2016, drone videos of narwhals surface - feeding in Tremblay Sound, Nunavut showed that the tusk was used to tap and stun small Arctic cod, making them easier to catch for feeding . </P>

Where does a narwhal's horn come from
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