Tusks are elongated, continuously growing front teeth, usually but not always in pairs, that protrude well beyond the mouth of certain mammal species. They are most commonly canines, as with warthogs, wild boar, and walruses, or, in the case of elephants and narwhals, elongated incisors. Tusks are generally curved, though the narwhal's sole tusk is straight and has a helical structure. In the elephant, the tusks were originally second incisors. Continuous growth is enabled by formative tissues in the apical openings of the roots of the teeth.[1][2]
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Tusks have a variety of uses depending on the animal. Social displays of dominance, particularly among males, are common, as is their use in defense against attackers. Elephants use them as digging and boring tools. Walruses use them to grip on ice and to haul out on ice.[3] The presence of tusks in only the male narwhals suggests that for these whales it is a secondary sexual characteristic.[4]
Tusks are used by humans to produce ivory, which is used in artifacts and jewelry, and formerly in other items such as piano keys. Consequently, many tusk bearing species have been hunted commercially and several are endangered. The ivory trade has been severely restricted by the United Nations Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
