Tusks
Tusks are elongated, continuously growing front teeth that protrude well beyond the mouth of certain mammal species. Most commonly known as canine teeth, as with narwhals, chevrotains, musk deer, water deer, muntjac, pigs, peccaries, hippopotamuses and walruses, or, in the case of elephants and hyrax, elongated incisors. Tusks share common features such as extra-oral position, growth pattern, composition and structure, and lack of contribution to ingestion. In most tusked species, both the males and the females have tusks, although males' are usually larger.Most mammals with tusks have a pair of them growing out from either side of the mouth. Tusks are generally curved and have a smooth, continuous surface. The male narwhal's straight single helical tusk, which usually grows out from the left of the mouth, is an exception to the typical features of tusks described above. Continuous growth of tusks is enabled by formative tissues in the apical openings of the roots of the teeth. Tusks vary in size: walrus tusks can reach over 95 centimetres (3.12 ft), narwhal tusks can reach 3 metres (9.8 ft), and the upward curving maxillary tusks of babirusa can reach lengths of over 20 centimetres (7.9 in).
Extinct mammals such as mammoths and mastodons exhibited a pair of large long upper tusks, both distant cousins of today's modern elephants. In contrast to mammals, dicynodonts are the only known vertebrates to have true tusks, tusks that grow continuously to perform species-specific functions as opposed to an enlarged tooth that resembles a traditional tusk and could be mistaken for one.
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