ناب خارجي

الفظ

Warthog

فيل

نرول

الناب الخارجي إنگليزية: Tusk هو سن قاطع طويل جدًا وقد يصل طوله حتى 3 أمتار لدى النرول يتكون من العاج ويوجد لدى بعض الثدييات مثل الفيل والفظ وكركدن البحر أو حريش البحر وكذلك الخنزير الوحشي الأفريقي ويقوم البشر بانتزاع الأنياب من أجل استخدام العاج في تصنيع المجوهرات لكن الأمم المتحدة سعت إلى مناهضة هذه الاعتداءات عبر اتفاقية الاتجار الدولي بالحيوانات والنباتات المهددة بالانقراض. In most tusked species both the males and the females have tusks although the males' are 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.

Other than mammals, dicynodonts are the only known vertebrates to have true tusks.

 الوظيفة

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 their tusks as digging and boring tools. Walruses use their tusks to grip and haul out on ice. It has been suggested that tusks' structure has evolved to be compatible with extra-oral environments.

 الحجم

Tusks of the mastodon "Mammut" borsoni from Greece, which, reaching over 5 متر (16 ft) in length, are the longest tusks ever recorded.

Elephant tusks are sexually dimorphic, being on average larger in males than in females, and entirely absent in female Asian elephants. Elephants with large tusks each at least 45 كيلوغرام (99 lb) in weight are known as "tuskers", sometimes also called "big tuskers" or "great tuskers". While tuskers are rare today, it is thought that they were more common in the past, prior to human impact on elephant populations. The two record holders for longest and heaviest recorded African bush elephant tusks are around 3.49 متر (11.5 ft) long measured along the outside curve, and 107 كيلوغرام (236 lb) in weight respectively, while the longest and heaviest Asian elephant tusks are 3.26 متر (10.7 ft) long and 73 كيلوغرام (161 lb) respectively. Even larger tusks are known from some extinct proboscideans, such as species of Stegodon, Palaeoloxodon, and mammoths, with the longest tusk ever recorded being that of a specimen of the gigantic mastodon "Mammut" borsoni from Greece, which measures 5.02 متر (16.5 ft) in length, with an estimated weight of 137 كيلوغرام (302 lb) with some mammoth tusks exceeding 4 متر (13 ft) in length and probably 200 كيلوغرام (440 lb) in weight. The largest walrus tusks can reach lengths of over 95 سنتيمتر (3.12 ft). The longest narwhal tusks reach 3 متر (9.8 ft). The upward curving maxillary tusks of babirusa can reach lengths of over 20 سنتيمتر (7.9 in).

 الاستخدام من البشر

Tusks are used by humans to produce ivory, which is used in artifacts and jewellery, 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).

Tusked animals in human care may undergo tusk trimming or removal for health and safety concerns. Furthermore, surgical veterinary procedures to remove tusks have been explored to mitigate human-wildlife conflicts.

 معرض

• 

  Walruses

• 

  Skull of Babyrousa celebensis, showing long upward curving canine tusks

• 

  Columbian mammoth

• 

  Tusks of a wild boar

• 

  Odobenocetops, an extinct whale with a long single tusk

 انظر أيضا

• Fang, a long canine tooth (in mammals)
• Ivory trade
• Eco-economic decoupling

 وصلات خارجية

• Carved Ivory Tusk
• Objects made from ivory and marine ivory in the collection of the Museum of New Zealand Te Papa Tongarewa