Teeth, fangs, and tusks

Teeth, fangs, and tusks are found in vertebrates and are used for obtaining and masticating food and for defense. Fangs and tusks are elongated canine or incisor teeth that serve to deliver venom (fangs) or as defensive weapons (tusks). Tusks, which are made of ivory, have been valued for making jewelry, decorative objects, and medicine, which has led to the endangerment of the elephants, rhinoceros, and walruses that carry them.

Teeth

Teeth are hard, resistant structures that are found on the jaws, as well as in or around the mouth and pharynx of vertebrates. Teeth were formed through the evolution of bony structures found in primitive fish. A tooth consists of a crown and one or more roots. The crown is the visible, functional part, while the root is attached to the tooth-bearing bone. However, many living organisms, such as birds, turtles, some species of whales, and many insects, do not have teeth.

Although the teeth of many vertebrates have been adapted for special uses, their function is to catch and masticate food and defend against predators or enemies, as well as other specific purposes. Rodents and rabbits, for instance, have curved incisors that are deeply embedded in the jaws and grow longer with age. Several types of apes have enlarged canines for defense, while the sawfish, which is the only animal with teeth completely outside its mouth, uses its teeth to attack its prey. All perissodactyls, a group of herbivorous animal species characterized by an odd number of toes on the hind foot, including horses, rhinoceroses, and tapirs, have evolved specialized forms of teeth that are adapted for grinding. Generally, lizards are insectivores and have sharp tricuspid teeth that are adapted for grabbing and holding. Mollusk and crustacean feeders, such as the caiman lizard, have blunt, rounded teeth along the jaw margin or on the palate.

Tooth-bearing animals may be heterodont or homodont. Most mammals are heterodont and carry two or more types of teeth, such as the incisors and the molars. The purpose of the incisors is to tear and bite into the food, while the molars crush and grind the food. Cats do not have flat-crowned crushing teeth; instead, only the stabbing and anchoring canine teeth cut up the food, which is then swallowed. In the case of elephants, the upper second incisors have developed into ivory tusks, which are the longest and heaviest teeth in any living animal. On the other hand, fish and most reptiles are homodonts—their teeth are all about the same size, and their purpose is to catch prey. This is the main reason why their teeth are regularly replaced during their life.

Snakes have teeth that curve back toward the throat. Thus, as soon as the prey is caught, it is pushed into the throat. In poisonous snakes, teeth called fangs have a canal through which the poison (venom), normally stored in glands that are in the roof of the mouth, may be ejected.

Hippopotamuses have the longest canine teeth of any land animal at 28 inches (71 centimeters) long. Conversely, among the animals with the smallest known teeth is the snail, which can have up to twelve thousand microscopic teeth called a radula made of chitin and goethite. These radula are located on the snail's tongue and are regularly replaced by newer teeth.

Fangs

Fangs are long, pointed teeth used by many animals for self-defense, for securing their prey, or for other reasons. Many snakes use their hollow fangs as hypodermic needles to puncture their victim and, in the case of a venomous snake, to inject toxic venom. Because of the snake’s muscular elasticity, the fang tips at penetration average 112 percent further apart than their bases at rest. The wound resulting from penetration of the flesh is called a snakebite. A nonvenomous snakebite is usually similar to a puncture wound which, when untreated, may become infected, and, in extreme cases, may cause gangrene. That of a venomous snake is much more serious. There is a potentially lethal effect, which depends on several factors such as the size of the victim, the bite location, the quantity of venom that has been injected, the speed of venom absorption into the victim’s blood circulation, and the speed with which first aid and the antidote are given.

Several venomous snakes, such as the ringhals and the black-necked cobra (types of African cobras), have the ability to spit. A fine stream of venom is forced out of each fang which, instead of having to go through a straight canal that ends in a long opening, is forced through a different canal that turns sharply forward to a small round opening on the front surface. Contraction of the muscle surrounding the poison gland leads to the spitting of the venom, which is harmful to human eyes unless washed quickly. Front-fanged snakes include pit vipers such as rattlesnakes, fixed-fanged snakes such as brown snakes and cobras, sea snakes, and true vipers (Viperidae). All have hollow, tubelike fangs created by the extension of the dentine across the anterior seam. Evolutionary herpetologists have postulated that this anterior seam may have been open several tens of thousands of years ago.

Only poisonous snakes possess fangs and venom glands, which are considered to be an evolutionary result of salivary glands found in primitive fish. Poisonous snakes bite the victim with their fangs and proceed to inject the venom into the wound to kill their prey. The venom contains toxins, which are chemical compounds that can potentially attack the blood and the nervous system with lethal consequences. The proteinaceous enzymes that are found in the venom are also used to digest the eaten animal. These snakes are generally subdivided into vipers and elapids. Vipers, which include copperheads and rattlesnakes, have long, movable front fangs, while elapids, such as cobras and rattlesnakes, have short front fangs that are fixed. Occasionally, some venomous snakes have a fang on the upper jaw in the rear of the mouth, which makes them less harmful to large animals since the venom injection occurs at a much slower pace. The devouring or swallowing of the prey usually takes place only after the venom has taken full effect and the animal is dead. Generally, small snakes embed their fangs in the prey longer than larger snakes.

The analysis and determination of the composition of the hard dental tissues of the Viperidae has been conducted using classical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and infrared spectroscopy. The results have shown a thin, calcified outer layer composed of very small needlelike crystals that are randomly distributed. The calcified outer layer contains pores and collagen fibers that are incompletely mineralized, especially in the wall of the poison canal. Chemical analysis of the dentine has indicated a poorly mineralized apatite with a high level of carbonate content.

All nine species that belong to the marine fish classified under the genus Chauliodus (order Salminoformes) are called viperfish. They are all small in size, the largest being the Pacific viperfish (C. macouni), which is no more than one foot long. They are characterized by their long fangs, which protrude from the upper and lower jaws and are used to securely grab their prey. The tigerfish of the Zambezi River, with its two rows of long and very sharp teeth, has been seen as more fearsome than the true piranha or the mako shark.

Tusks

Evolutionary theories suggest that the tusks of both the walrus and the wild boar are enlarged canine teeth, while in the case of the pig, the lower incisor has been modified with time into an organ that is used for digging purposes. In male Indian elephants and African elephants of both sexes, the tusk is the upper incisor, which continues to grow throughout their lifetime. The female Indian elephant has either no tusks or very small ones. Male Ceylonese elephants, found in Sri Lanka, generally have no tusks, while Sumatran elephants, found in Indonesia, bear the longest tusks. Elephant tusks from Africa are typically six feet long, conical at the end, and weigh approximately fifty pounds each. Indian elephants have slightly smaller tusks. Each tusk from the largest pair, recorded and exhibited at the British Museum, is twelve feet long, has a barrel circumference of eighteen inches, and weighs close to 150 pounds.

Studies by Raman Sukumar, an ecologist at the Indian Institute of Science in Bangalore, and Milind Watve, a microbiologist, indicate that male Asian elephants with longer tusks are prone to host many fewer parasites. This is in agreement with the theory of the evolutionary biologist William D. Hamilton of the University of Oxford, who proposed in 1982 that males that carry genes resistant to parasites have the ability to be healthier and, therefore, live longer. At the same time, these species develop secondary sexual characteristics which enable females to select males that will produce better offspring.

Anatomically, the tusk comprises several layers, the innermost growing the latest. One-third of the tusk is embedded in the bone sockets of the elephant’s skull. At its beginning, the head end of the tusk has a hollow cavity that becomes almost fully solid with aging. Only a narrow nerve channel runs through the center of the tusk to its end.

Ivory is a type of dentin that is the major component of the elephant tusk and is desirable worldwide for its beauty and durability. There are generally two types of ivory, soft and hard. The ivory isolated from the tusks of East African elephants is soft, while that found in the West African elephants is hard. Hard ivory is usually darker in color and straighter than the soft type, which has a fibrous internal texture, is less brittle, and is a more opaque white. The demand for ivory has led to many elephant slaughtering incidents and a dangerous decline in the African elephant population, beginning in the late nineteenth century and continuing up to the twenty-first. The discovery by archaeologists in the early 1980s of tusk material in a Greek ship that was sunk around 1400 BCE revealed that ivory was a trade commodity even during the Bronze Age.

In 1990, an international ivory trade ban went into effect, aiming to lower the elephant and rhinoceros poaching rates. However, 2011 was the worst year for elephant death rates due to the ivory trade. Although efforts have been made to eradicate the ivory trade, it was estimated late into the 2010s and again in the early 2020s that as many as 20,000 African elephants continued to be slaughtered annually despite ivory bans. Vietnam, Cambodia, and Malaysia serve as major hubs for ivory trafficking, and countries in Asia are the primary consumers. The ivory trade not only endangers animals but also has lasting effects on ecosystems and the people who live close to the animals.

Elephants belong to the order Proboscidea, whose early ancestors were not larger than the average pig. It is believed that during the process of evolution, the lower jaw elongated beyond the upper and eventually turned into tusks. As a result, the nose and upper lips developed into an elongated cover to the projecting lower jaw. During the Eocene Epoch (between fifty-four and forty million years ago), the upper tusks were lost, and a downward-hooked, tusk-tipped mandible developed. The mandible and its tusks became more shovel-like during the Miocene era (twenty-six to seven million years ago). It is believed that the tusks assumed a cylindrical shape not very much later. It appears that tusks were also part of the anatomy of the woolly mammoth, as seen in the specimen that died about twenty thousand years ago and was discovered in a Siberian excavation in the 1990s.

Principal Terms

Elapids: a snake classification that includes cobras and rattlesnakes that have short, fixed front fangs

Heterodont: having two or more types of teeth, such as molars and incisors

Homodont: having teeth all of the same type

Incisor Teeth: teeth that are located in the front of the mouth and whose function is to tear, hold, and cut the prey

Toxin: any substance, such as the venom in snakes or spiders, that is toxic to an animal

Viperidae: poisonous terrestrial or semiaquatic snakes

Vipers: a snake classification that includes copperheads and rattlesnakes, which have long, movable front fangs

Bibliography

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