Elephant
Elephants are the largest living land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. 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.
Elephants are scattered throughout sub-Saharan Africa, South Asia, and Southeast Asia and are found in different habitats, including savannahs, forests, deserts, and marshes. They are herbivorous, and they stay near water when it is accessible. They are considered to be keystone species, due to their impact on their environments. Elephants have a fission–fusion society, in which multiple family groups come together to socialise. Females tend to live in family groups, which can consist of one female with her calves or several related females with offspring. The leader of a female group, usually the oldest cow, is known as the matriarch.
Males 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 on the IUCN Red Lists. 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.
Etymology
The word elephant is derived from the Latin word elephas , which is the Latinised form of the ancient Greek ἐλέφας probably from a non-Indo-European language, likely Phoenician. It is attested in Mycenaean Greek as in Linear B syllabic script. As in Mycenaean Greek, Homer used the Greek word to mean ivory, but after the time of Herodotus, it also referred to the animal. The word elephant appears in Middle English as olyfaunt in and was borrowed from Old French oliphant in the 12th century.Taxonomy
Elephants belong to the family Elephantidae, the sole remaining family within the order Proboscidea. Their closest extant relatives are the sirenians and the hyraxes, with which they share the clade Paenungulata within the superorder Afrotheria. Elephants and sirenians are further grouped in the clade Tethytheria.Three species of living elephants are recognised; the African bush elephant, forest elephant, and Asian elephant. African elephants were traditionally considered a single species, Loxodonta africana, but molecular studies have affirmed their status as separate species. Mammoths are nested within living elephants as they are more closely related to Asian elephants than to African elephants. 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. Palaeoloxodon was even larger than modern species, all exceeding 4 metres in height and 10 tonnes in body mass, with P. namadicus being a contender for the largest land mammal to have ever existed.
Evolution
The earliest members of Proboscidea like Eritherium are known from the Paleocene of Africa, around 60 million years ago, the earliest proboscideans were much smaller than living elephants, with Eritherium having a body mass of around. By the late Eocene, some members of Proboscidea like Barytherium had reached considerable size, with an estimated mass of around 2 tonnes, while others like Moeritherium are suggested to have been semi-aquatic.A major event in proboscidean evolution was the collision of Afro-Arabia with Eurasia, during the Early Miocene, around 18–19 million years ago, allowing proboscideans to disperse from their African homeland across Eurasia and later, around 16–15 million years ago into North America across the Bering Land Bridge. Proboscidean groups prominent during the Miocene include the deinotheres, along with the more advanced elephantimorphs, including mammutids, gomphotheres, amebelodontids, choerolophodontids and stegodontids. Around 10 million years ago, the earliest members of the family Elephantidae emerged in Africa, having originated from gomphotheres.
Elephantids are distinguished from earlier proboscideans by a major shift in the molar morphology to parallel lophs rather than the cusps of earlier proboscideans, allowing them to become higher-crowned and more efficient in consuming grass. The Late Miocene saw major climactic changes, which resulted in the decline and extinction of many proboscidean groups. The earliest members of the modern genera of elephants as well as mammoths, appeared in Africa during the latest Miocene–early Pliocene around 7-4 million years ago. The elephantid genera Elephas and Mammuthus migrated out of Africa during the late Pliocene, around 3.6 to 3.2 million years ago.
Over the course of the Early Pleistocene, all non-elephantid proboscidean genera outside of the Americas became extinct with the exception of Stegodon, with gomphotheres dispersing into South America as part of the Great American interchange, and mammoths migrating into North America around 1.5 million years ago. 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. 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 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.
Over the course of their evolution, proboscideans 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 became longer and more specialised. The incisors developed into tusks of different shapes and sizes. Several species of proboscideans became isolated on islands and experienced insular dwarfism, some dramatically reducing in body size, such as the tall dwarf elephant species Palaeoloxodon falconeri.
Living species
Anatomy
Elephants are the largest living terrestrial animals. The skeleton is made up of 326–351 bones. The vertebrae are connected by tight joints, which limit the backbone's flexibility. African elephants have 21 pairs of ribs, while Asian elephants have 19 or 20 pairs. The skull contains air cavities that reduce the weight of the skull while maintaining overall strength. These cavities give the inside of the skull a honeycomb-like appearance. By contrast, the lower jaw is dense. The cranium is particularly large and provides enough room for the attachment of muscles to support the entire head. The skull is built to withstand great stress, particularly when fighting or using the tusks. The brain is surrounded by arches in the skull, which serve as protection. Because of the size of the head, the neck is relatively short to provide better support.Elephants are homeotherms and maintain their average body temperature at ~ 36 °C, with a minimum of 35.2 °C during the cool season, and a maximum of 38.0 °C during the hot dry season.
Ears and eyes
Elephant ear flaps, or pinnae, are thick in the middle with a thinner tip and supported by a thicker base. They contain numerous blood vessels called capillaries. Warm blood flows into the capillaries, releasing excess heat into the environment. This effect is increased by flapping the ears back and forth. Larger ear surfaces contain more capillaries, and more heat can be released. Of all the elephants, African bush elephants live in the hottest climates and have the largest ear flaps. The ossicles are adapted for hearing low frequencies, being most sensitive at 1 kHz.Lacking a lacrimal apparatus, 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. Elephants are dichromats and they can see well in dim light but not in bright light.