4 Elephant

[Desiree Friede]

Elephantsare the largest living land animals. Three living species are currently recognised: the African bush elephant (Loxodonta africana), the African forest elephant (L. cyclotis), and the Asian elephant (Elephas maximus). They are the only surviving members of the family Elephantidae and the order Proboscidea; extinct relatives include mammoths and mastodons. Distinctive features of elephants include a long proboscis called a trunk, tusks, large ear flaps, pillar-like legs, and tough but sensitive grey skin. The trunk is prehensile, bringing food and water to the mouth and grasping objects. Tusks, which are derived from the incisor teeth, serve both as weapons and as tools for moving objects and digging. The large ear flaps assist in maintaining a constant body temperature as well as in communication. African elephants have larger ears and concave backs, whereas Asian elephants have smaller ears and convex or level backs.

Males (bulls) leave their family groups when they reach puberty and may live alone or with other males. Adult bulls mostly interact with family groups when looking for a mate. They enter a state of increased testosterone and aggression known as musth, which helps them gain dominance over other males as well as reproductive success. Calves are the centre of attention in their family groups and rely on their mothers for as long as three years. Elephants can live up to 70 years in the wild. They communicate by touch, sight, smell, and sound; elephants use infrasound and seismic communication over long distances. Elephant intelligence has been compared with that of primates and cetaceans. They appear to have self-awareness, and possibly show concern for dying and dead individuals of their kind.

African bush elephants and Asian elephants are listed as endangered and African forest elephants as critically endangered by the International Union for Conservation of Nature (IUCN). One of the biggest threats to elephant populations is the ivory trade, as the animals are poached for their ivory tusks. Other threats to wild elephants include habitat destruction and conflicts with local people. Elephants are used as working animals in Asia. In the past, they were used in war; today, they are often controversially put on display in zoos, or employed for entertainment in circuses. Elephants have an iconic status in human culture and have been widely featured in art, folklore, religion, literature, and popular culture.

Elephants belong to the family Elephantidae, the sole remaining family within the order Proboscidea. Their closest extant relatives are the sirenians (dugongs and manatees) and the hyraxes, with which they share the clade Paenungulata within the superorder Afrotheria.[6] Elephants and sirenians are further grouped in the clade Tethytheria.[7]

Three species of living elephants are recognised; the African bush elephant (Loxodonta africana), forest elephant (Loxodonta cyclotis), and Asian elephant (Elephas maximus).[8] African elephants were traditionally considered a single species, Loxodonta africana, but molecular studies have affirmed their status as separate species.[9][10][11] Mammoths (Mammuthus) are nested within living elephants as they are more closely related to Asian elephants than to African elephants.[12] Another extinct genus of elephant, Palaeoloxodon, is also recognised, which appears to have close affinities with African elephants and to have hybridised with African forest elephants.[13]

Over 180 extinct members of order Proboscidea have been described.[14] The earliest proboscideans, the African Eritherium and Phosphatherium are known from the late Paleocene.[15] The Eocene included Numidotherium, Moeritherium, and Barytherium from Africa. These animals were relatively small and, some, like Moeritherium and Barytherium were probably amphibious.[16][17] Later on, genera such as Phiomia and Palaeomastodon arose; the latter likely inhabited more forested areas. Proboscidean diversification changed little during the Oligocene.[16] One notable species of this epoch was Eritreum melakeghebrekristosi of the Horn of Africa, which may have been an ancestor to several later species.[18]

Over the course of the Early Pleistocene, all non-elephantid probobscidean genera outside of the Americas became extinct with the exception of Stegodon,[21] with gomphotheres dispersing into South America as part of the Great American interchange,[25] and mammoths migrating into North America around 1.5 million years ago.[26] At the end of the Early Pleistocene, around 800,000 years ago the elephantid genus Palaeoloxodon dispersed outside of Africa, becoming widely distributed in Eurasia.[27] Proboscideans were represented by around 23 species at the beginning of the Late Pleistocene. Proboscideans underwent a dramatic decline during the Late Pleistocene as part of the Late Pleistocene extinctions of most large mammals globally, with all remaining non-elephantid proboscideans (including Stegodon, mastodons, and the American gomphotheres Cuvieronius and Notiomastodon) and Palaeoloxodon becoming extinct, with mammoths only surviving in relict populations on islands around the Bering Strait into the Holocene, with their latest survival being on Wrangel Island, where they persisted until around 4,000 years ago.[21][28]

Over the course of their evolution, probobscideans grew in size. With that came longer limbs and wider feet with a more digitigrade stance, along with a larger head and shorter neck. The trunk evolved and grew longer to provide reach. The number of premolars, incisors, and canines decreased, and the cheek teeth (molars and premolars) became longer and more specialised. The incisors developed into tusks of different shapes and sizes.[29] Several species of proboscideans became isolated on islands and experienced insular dwarfism,[30] some dramatically reducing in body size, such as the 1 m (3 ft 3 in) tall dwarf elephant species Palaeoloxodon falconeri.[31]

Lacking a lacrimal apparatus (tear duct), the eye relies on the harderian gland in the orbit to keep it moist. A durable nictitating membrane shields the globe. The animal's field of vision is compromised by the location and limited mobility of the eyes.[43] Elephants are dichromats[44] and they can see well in dim light but not in bright light.[45]

As a muscular hydrostat, the trunk moves through finely controlled muscle contractions, working both with and against each other.[47] Using three basic movements: bending, twisting, and longitudinal stretching or retracting, the trunk has near unlimited flexibility. Objects grasped by the end of the trunk can be moved to the mouth by curving the appendage inward. The trunk can also bend at different points by creating stiffened "pseudo-joints". The tip can be moved in a way similar to the human hand.[48] The skin is more elastic on the dorsal side of the elephant trunk than underneath; allowing the animal to stretch and coil while maintaining a strong grasp.[49] The African elephants have two finger-like extensions at the tip of the trunk that allow them to pluck small food. The Asian elephant has only one and relies more on wrapping around a food item.[33] Asian elephant trunks have better motor coordination.[46]

The trunk's extreme flexibility allows it to forage and wrestle other elephants with it. It is powerful enough to lift up to 350 kg (770 lb), but it also has the precision to crack a peanut shell without breaking the seed. With its trunk, an elephant can reach items up to 7 m (23 ft) high and dig for water in the mud or sand below. It also uses it to clean itself.[50] Individuals may show lateral preference when grasping with their trunks: some prefer to twist them to the left, others to the right.[47] Elephant trunks are capable of powerful siphoning. They can expand their nostrils by 30%, leading to a 64% greater nasal volume, and can breathe in almost 30 times faster than a human sneeze, at over 150 m/s (490 ft/s).[51] They suck up water, which is squirted into the mouth or over the body.[29][51] The trunk of an adult Asian elephant is capable of retaining 8.5 L (2.2 US gal) of water.[46] They will also sprinkle dust or grass on themselves.[29] When underwater, the elephant uses its trunk as a snorkel.[52]

The trunk also acts as a sense organ. Its sense of smell may be four times greater than a bloodhound's nose.[53] The infraorbital nerve, which makes the trunk sensitive to touch, is thicker than both the optic and auditory nerves. Whiskers grow all along the trunk, and are particularly packed at the tip, where they contribute to its tactile sensitivity. Unlike those of many mammals, such as cats and rats, elephant whiskers do not move independently ("whisk") to sense the environment; the trunk itself must move to bring the whiskers into contact with nearby objects. Whiskers grow in rows along each side on the ventral surface of the trunk, which is thought to be essential in helping elephants balance objects there, whereas they are more evenly arranged on the dorsal surface. The number and patterns of whiskers are distinctly different between species.[54]

Damaging the trunk would be detrimental to an elephant's survival,[29] although in rare cases, individuals have survived with shortened ones. One trunkless elephant has been observed to graze using its lips with its hind legs in the air and balancing on its front knees.[46] Floppy trunk syndrome is a condition of trunk paralysis recorded in African bush elephants and involves the degeneration of the peripheral nerves and muscles. The disorder has been linked to lead poisoning.[55]

Elephants are usually right- or left-tusked, similar to humans, who are typically right- or left-handed. The dominant, or "master" tusk, is typically more worn down, as it is shorter and blunter. For African elephants, tusks are present in both males and females and are around the same length in both sexes, reaching up to 300 cm (9 ft 10 in),[57] but those of males tend to be more massive.[58] In the Asian species, only the males have large tusks. Female Asians have very small tusks, or none at all.[57] Tuskless males exist and are particularly common among Sri Lankan elephants.[59] Asian males can have tusks as long as Africans', but they are usually slimmer and lighter; the largest recorded was 302 cm (9 ft 11 in) long and weighed 39 kg (86 lb). Hunting for elephant ivory in Africa[60] and Asia[61] has led to natural selection for shorter tusks[62][63] and tusklessness.[64][65]

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