Tusk

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.thumb|Tusks of the mastodon [["Mammut" borsoni from Greece, which, reaching over in length, are the longest tusks ever recorded.]]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.

Function

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 themselves onto ice. It has been suggested that tusks' structure has evolved to be compatible with extra-oral environments. The largest walrus tusks can reach lengths of over . The longest narwhal tusks reach . The upward curving maxillary tusks of babirusa can reach lengths of over .

Hyrax:

center|thumb|Hyrax tusks

In contrast to the variety of large sized tusks, there are tusks that are small and unassuming within the Paenungulata (elephants, sirenians, and hyraxes) clade. The Hyrax, a herbivorous mammal commonly found in Ethiopia and southern Africa, exhibit ever-growing tusk-like incisors. Hyrax tusks are hypertrophied. They have grown to be enlarged far beyond what is considered typical for the average tooth. While they are not considered true tusks like in elephants, the hyrax tusk-like incisors have overgrown to the point of the traditional tusk-like appearance. Composed of only dentin and a thin layer of enamel, the hyrax tusks are triangular in shape and serve no observed function for feeding.

Hippo:

thumb|Hippo Tusks |center

Hippopatamus tusks are derived from lower canine teeth, composed of an outer layer, cementum, and an interior of dentine, or ivory. Being hypselodont, the tusks and incisors of the Hippopotamus is ever growing and rootless, allowing for continual rejuvenation through everyday wear and tear through diet and defensive mechanisms like fighting, and sharpening from the vertical motion against the shorter upper canines. The size of the tusk is a sexual-dimorphic trait, with the tusk of males growing up to 50 cm (1.5 ft), double the size of female tusks. There are many different species of wild boars that take up different ecological niches in the world including deserts, grasslands, forested regions, and more. Wild boars are typically omnivorous and have a range of different diets depending on season and habitat. In wild boar species the upper and lower canines are ever-growing tusks made of 80% dentin covered in enamel, and a large centre pulp cavity. The lower canine tusk is often longer than the upper canine tusk, but is kept short due to the upper canine wearing down the bottom, preventing overgrowth into the mouth cavity. There is often sexual dimorphism present in wild boar species, with differences in overall body size (smaller females), and smaller canine tusks in females. The upper canines in males will often curve upwards and dorsally, which differs from female upper canines that extend laterally.

Ruminants:

thumb|Chinese Water deer

Ruminantia are often remembered for their horns, but there are also a few unique species with prominent upper canine tusks. Species such as the musk deer, tufted deer, Chinese water deer, and reeves muntjac all have upper canine tusks. In these species there is a clear sexual dimorphism with the female canine tusks being significantly reduced compared to the male tusks. The pronounced upper canines in males are typically used in aggressive encounters with other males. A hypothesized reason for having enlarged canine tusks for intra-specific competition, instead of horns normally associated with ruminants, is due to the size of animal and their type of habitat. Larger ruminants with more elaborate horns or head ornaments often live in open environments, and ruminants with tusks are often smaller and live in denser habitats where head ornaments may not be beneficial. There are three known subspecies of walruses relating to their geographic ranges within the Arctic: the pacific walrus (Odobenus rosmarus divergens), the atlantic walrus (Odobenus rosmarus rosmarus), and the laptev walrus being the smallest subspecies found in the Laptev sea (Odobarus rosmarus laptevi).

thumb|Walrus skull and tusks

Walruses are pinnipeds a clade within the order Carnivora, characterizing these enlarged maxillary tusks as canines. Walrus tusks are described as aradicular hypsodont (elodont) teeth, meaning they develop and erupt continuously while having no true roots. Tusks are embedded within the jaw by the periodontium, composed of different layers as seen in elephants and hippos, with a cementum outer layer and a dentin (ivory) inner layer. Differences associated with mating behaviours and competition between other males. Walruses exhibit polygynous mating systems, where one male mates with multiple females. To defend these territories of females, males will use tusks to establish dominance and fight if needed. Thus tusks play an important role in social interactions and reproductive success. The Marine Mammal Protection Act in the US, permits communities to sell or trade authentic handicrafts. Organizations such as WWF support legislations ARTIST Act and Archie Cavanaugh Migratory Bird Treaty Amendment Act, addressing any legal or economic challenges Indigenous communities may face while creating handicrafts. Providing Indigenous cultural practices autonomy and legal protection, maintaining artistic traditions that use legally obtained walrus ivory.

Fossil ivory such as mammoth tusks came into high demand following international restrictions on the elephant ivory trade. In the Russian Arctic region of northeastern Siberia (Yakutia) live the Indigenous people of the Republic of Sakha, where mammoth tusk collection provides income to these local communities. However, environmental concerns relating to extraction methods may cause damage to tundra landscapes and permafrost.

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.

Function

Hyrax:

Hippo:

Ruminants:

Gallery

See also

References