elephant

The trunk (proboscis)

The trunk, or proboscis, of the elephant is one of the most versatile organs to have evolved among mammals. This structure is unique to members of the order Proboscidea, which includes the extinct mastodons and mammoths. Anatomically, the trunk is a combination of the upper lip and nose; the nostrils are located at the tip. The trunk is large and powerful, weighing about 130 kg (290 pounds) in an adult male and capable of lifting a load of about 250 kg. However, it is also extremely dexterous, mobile, and sensitive, which makes it appear almost independent of the rest of the animal. The proboscis comprises 16 muscles. A major muscle covering the top and sides functions to raise the trunk; another covers the bottom. Within the trunk is an extremely complex network of radiating and transverse muscle fascicles that provide fine movement. A total of nearly 150,000 muscle fascicles have been counted in cross sections of trunk. The trunk is innervated by two proboscidean nerves, which render it extremely sensitive. Bifurcations of this nerve reach most portions of the trunk, especially the tip, which is equipped with tactile bristles at regular intervals. At the end of the trunk are flaplike projections enabling it to perform amazingly delicate functions, such as picking up a coin from a flat surface or cracking a peanut open, blowing away the shell, and putting the kernel in the mouth. African elephants have two such extremities (one above and one below); Asian elephants have one. An Asian elephant most often curls the tip of its trunk around an item and picks it up in a method called the “grasp,” whereas the African elephant uses the “pinch,” picking up objects in a manner similar to that of a human’s use of the thumb and index finger. The trunk of the African elephant may be more extendable, but that of the Asian elephant is probably more dexterous.

Elephants use the trunk like a hand in other ways as well. Tool use in elephants involves holding branches and scratching themselves in places that the trunk and tail cannot reach. Large branches are sometimes wielded, and objects may be thrown in threat displays. When elephants meet, one may touch the face of the other, or they will intertwine trunks. This “trunk-shake” can be compared to a human handshake in that it may be associated with similar functions such as assurance and greeting or as a way of assessing strength.

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Breathing, drinking, and eating are all vital functions of the trunk. Most breathing is performed through the trunk rather than the mouth. Elephants drink by sucking as much as 10 litres (2.6 gallons) of water into the trunk and then squirting it into the mouth. They eat by detaching grasses, leaves, and fruit with the end of the trunk and using it to place this vegetation into the mouth. The trunk is also used to collect dust or grass for spraying onto themselves, presumably for protection against insect bites and the sun. If danger is suspected, elephants raise and swivel the trunk as if it were “an olfactory periscope,” possibly sniffing the air for information.

Sound production and water storage

Elephants produce two types of vocalization by modifying the size of the nostrils as air is passed through the trunk. Low sounds are the growl, rolling growl, snort, and roar; high sounds are the trump, trumpet, pulsated trumpet, trumpet phrase, bark, gruff cry, and cry. Rumbling sounds initially thought to be caused by intestinal activity are now known to be produced by the voice box (larynx) and are considered to be similar to purring in cats. Vocalizations originate in the larynx and a special structure associated with it, the pharyngeal pouch. In the vast majority of mammals, the throat contains nine bones connected in a boxlike structure, the hyoid apparatus, that supports the tongue and the voice box. Elephants have only five bones in the hyoid apparatus, and the gap formed by the missing bones is filled by muscles, tendons, and ligaments. These looser attachments allow the larynx a great degree of freedom and enable the formation of the pharyngeal pouch just behind the tongue. This unique structure facilitates sound production and has voluntary muscles that allow the pouch to be used as a resonating chamber for calls emitted at frequencies below the range of human hearing. These low-frequency (5–24 hertz) calls are responded to by other elephants up to 4 km (2.5 miles) away. Low-frequency sound waves travel through the ground as well as the air, and results of experiments indicate that elephants can detect infrasonic calls as seismic waves. Elephants can produce a variety of other sounds by beating the trunk on hard ground, a tree, or even against their own tusks.

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In addition to sound production, the pharyngeal pouch is presumed to be used for carrying water. For centuries people have observed that on hot days and in times when there is no water nearby, elephants insert their trunks into their mouths, withdraw liquid, and spray themselves with it. The source of this liquid and the ability of elephants to withdraw it have posed a mystery even though the pharyngeal pouch was described in 1875. Two plausible sources of the liquid are the stomach and the pharyngeal pouch. Stomach contents, however, are acidic and would irritate the skin. In addition, the sprayed liquid contains small food particles commonly found in the pharyngeal pouch, as opposed to digested food from the stomach. Finally, repeated field observations attest that elephants can spray themselves while walking or running. As it would be difficult to suck liquid from the stomach while running, the most likely explanation for the liquid’s source is the pharyngeal pouch. Another possible function of the pouch is heat absorption, especially from the sensitive brain area above it.

Tusks and teeth

Elephant tusks are enlarged incisor teeth made of ivory. In the African elephant both the male and the female possess tusks, whereas in the Asian elephant it is mainly the male that has tusks. When present in the female, tusks are small, thin, and often of a uniform thickness. Some male Asian elephants are tuskless and are known as muknas. Tusk size and shape are inherited. Tusks are used for defense, offense, digging, lifting objects, gathering food, and stripping bark to eat from trees. They also protect the sensitive trunk, which is tucked between them when the elephant charges. In times of drought, elephants dig water holes in dry riverbeds by using their tusks, feet, and trunks.

Elephants have six sets of cheek teeth (molars and premolars) in their lifetime, but they do not erupt all at once. At birth an elephant has two or three pairs of cheek teeth in each jaw. New teeth develop from behind and slowly move forward as worn teeth fragment in front and either fall out or are swallowed and excreted. Each new set is successively longer, wider, and heavier. The last molars can measure nearly 40 cm (almost 16 inches) long and weigh more than 5 kg (about 11 pounds). Only the last four molars or their remains are present after about 60 years of age. Sometimes tooth loss is the cause of death, as it brings on starvation.