Title: Narwhal - Wikipedia
Headings: Narwhal
Narwhal
Contents
Taxonomy and etymology
Description
Tusk
Vestigial teeth
Genome
Distribution
Behaviour
Social
Migration
Diet
Diving
Communication
Breeding and early life
Life span and mortality
Predation and hunting
Conservation issues
Cultural depictions
In legend
In literature and art
Gallery
See also
References
Further reading
External links

Content: The most conspicuous characteristic of the male narwhal is a single long tusk, which is in fact a canine tooth that projects from the left side of the upper jaw, through the lip, and forms a left-handed helix spiral. The 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). Scientists have long speculated on the biological function of the tusk. Proposed functions include use of the tusk as a weapon, for opening breathing holes in sea ice, in feeding, as an acoustic organ, and as a secondary sex character. The leading theory has long been that the narwhal tusk serves as a secondary sex character of males, for nonviolent assessment of hierarchical status on the basis of relative tusk size. However, detailed analysis reveals that the tusk is a highly innervated sensory organ with millions of nerve endings connecting seawater stimuli in the external ocean environment with the brain.