Elephant

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This article is about a paraphyletic group. For close extinct relatives, see Elephantidae. For other uses, see Elephant (disambiguation).

Elephants

Temporal range: Pliocene–Present

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From top left to right: the African bush elephant, the Asian elephant and African forest elephant.

From top left to right: the African bush elephant, the Asian elephant and African forest elephant.

Scientific classificationEdit this classification

Kingdom:Animalia

Phylum:Chordata

Class:Mammalia

Order:Proboscidea

Family:Elephantidae

Subfamily:Elephantinae

Groups included

Loxodonta Anonymous, 1827

Elephas Linnaeus, 1758

†Palaeoloxodon Matsumoto, 1925

Cladistically included but traditionally excluded taxa

†Mammuthus Brookes, 1828

†Primelephas Maglio, 1970

Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are an informal grouping within the proboscidean family Elephantidae. Elephantidae is the only surviving family of proboscideans; extinct members include the mastodons. Elephantidae also contains several extinct groups, including the mammoths and straight-tusked elephants. African elephants have larger ears and concave backs, whereas Asian elephants have smaller ears, and convex or level backs. Distinctive features of all elephants include a long proboscis called a trunk, tusks, large ear flaps, massive legs, and tough but sensitive skin. The trunk is used for breathing, 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. The pillar-like legs carry their great weight.

 

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 (cows) tend to live in family groups, which can consist of one female with her calves or several related females with offspring. The groups, which do not include bulls, are usually led by the oldest cow, known as the matriarch.

 

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 appear to show empathy for dying and dead family members.

 

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 exploited for entertainment in circuses. Elephants are highly recognisable and have been featured in art, folklore, religion, literature, and popular culture.

Etymology

The word "elephant" is based on the Latin elephas (genitive elephantis) ("elephant"), which is the Latinised form of the Greek ἐλέφας (elephas) (genitive ἐλέφαντος (elephantos[1]), probably from a non-Indo-European language, likely Phoenician.[2] It is attested in Mycenaean Greek as e-re-pa (genitive e-re-pa-to) in Linear B syllabic script.[3][4] As in Mycenaean Greek, Homer used the Greek word to mean ivory, but after the time of Herodotus, it also referred to the animal.[1] The word "elephant" appears in Middle English as olyfaunt (c.1300) and was borrowed from Old French oliphant (12th century).[2]

 

Taxonomy and phylogeny

Afrotheria

Afroinsectiphilia

Tubulidentata

Orycteropodidae Aardvark2 (PSF) colourised.png

 

 

Afroinsectivora

Macroscelidea

Macroscelididae Rhynchocyon chrysopygus-J Smit white background.jpg

 

 

Afrosoricida

 

Chrysochloridae The animal kingdom, arranged according to its organization, serving as a foundation for the natural history of animals (Pl. 18) (Chrysochloris asiatica).jpg

 

 

 

Tenrecidae Brehms Thierleben - Allgemeine Kunde des Thierreichs (1876) (Tenrec ecaudatus).jpg

 

 

 

 

 

Paenungulata

Hyracoidea

Procaviidae DendrohyraxEminiSmit white background.jpg

 

 

Tethytheria

Proboscidea

Elephantidae Elephas africanus - 1700-1880 - Print - Iconographia Zoologica - (white background).jpg

 

 

Sirenia

 

Dugongidae Dugong dugon Hardwicke white background.jpg

 

 

 

Trichechidae Manatee white background.jpg

 

 

 

 

 

 

A cladogram of the elephants within Afrotheria based on molecular evidence[5]

Proboscidea

 

early proboscideans, e.g. Moeritherium Moeritherium NT small.jpg

 

 

 

 

Deinotheriidae Deinotherium12.jpg

 

 

Elephantiformes

 

Mammutidae BlankMastodon.jpg

 

 

 

 

Gomphotheriidae Gomphotherium NT small.jpg

 

 

 

 

Stegodontidae Stegodon Siwalik Hills.jpg

 

 

Elephantidae

 

Loxodonta African Bush Elephant.jpg

 

 

 

 

Mammuthus Mammuthus trogontherii122DB.jpg

 

 

 

Elephas Elephas maximus (Bandipur).jpg

 

 

 

 

 

 

 

 

 

Proboscidea phylogeny based on upper molars.[6]

Elephantimorpha

Elephantidae

 

 

 

Mammuthus primigenius Woolly mammoth model Royal BC Museum in Victoria.jpg

 

 

 

Mammuthus columbi Archidiskodon imperator121.jpg

 

 

 

 

Elephas maximus Elephas maximus (Bandipur).jpg

 

 

 

 

 

 

Loxodonta cyclotis African Forest Elephant.jpg

 

 

 

Palaeoloxodon antiquus Elephas-antiquus.jpg

 

 

 

 

Loxodonta africana African Bush Elephant.jpg

 

 

 

 

 

Mammut americanum BlankMastodon.jpg

 

 

 

Phylogeny of modern elephants and close extinct relatives based on molecular evidence[7]

See also: List of elephant species

Elephants belong to the family Elephantidae, the sole remaining family within the order Proboscidea which belongs to the superorder Afrotheria. Their closest extant relatives are the sirenians (dugongs and manatees) and the hyraxes, with which they share the clade Paenungulata within the superorder Afrotheria.[8] Elephants and sirenians are further grouped in the clade Tethytheria.[9]

 

Three species of elephants are recognised; the African bush elephant (Loxodonta africana) and forest elephant (Loxodonta cyclotis) of sub-Saharan Africa, and the Asian elephant (Elephas maximus) of South and Southeast Asia.[10] African elephants have larger ears, a concave back, more wrinkled skin, a sloping abdomen, and two finger-like extensions at the tip of the trunk. Asian elephants have smaller ears, a convex or level back, smoother skin, a horizontal abdomen that occasionally sags in the middle and one extension at the tip of the trunk. The looped ridges on the molars are narrower in the Asian elephant while those of the African are more diamond-shaped. The Asian elephant also has dorsal bumps on its head and some patches of depigmentation on its skin.[11]

 

Among African elephants, forest elephants have smaller and more rounded ears and thinner and straighter tusks than bush elephants and are limited in range to the forested areas of western and Central Africa.[12] Both were traditionally considered a single species, Loxodonta africana, but molecular studies have affirmed their status as separate species.[13][14][15] In 2017, DNA sequence analysis showed that L. cyclotis is more closely related to the extinct Palaeoloxodon antiquus, than it is to L. africana, possibly undermining the genus Loxodonta as a whole.[16]

 

Evolution and extinct relatives

Over 180 extinct members and three major evolutionary radiations of the order Proboscidea have been recorded.[17] The earliest proboscids, the African Eritherium and Phosphatherium of the late Paleocene, heralded the first radiation.[18] The Eocene included Numidotherium, Moeritherium, and Barytherium from Africa. These animals were relatively small and aquatic. Later on, genera such as Phiomia and Palaeomastodon arose; the latter likely inhabited forests and open woodlands. Proboscidean diversity declined during the Oligocene.[19] One notable species of this epoch was Eritreum melakeghebrekristosi of the Horn of Africa, which may have been an ancestor to several later species.[20] The beginning of the Miocene saw the second diversification, with the appearance of the deinotheres and the mammutids. The former were related to Barytherium and lived in Africa and Eurasia,[21] while the latter may have descended from Eritreum[20] and spread to North America.[21]

 

The second radiation was represented by the emergence of the gomphotheres in the Miocene,[21] which likely evolved from Eritreum[20] and originated in Africa, spreading to every continent except Australia and Antarctica. Members of this group included Gomphotherium and Platybelodon.[21] The third radiation started in the late Miocene and led to the arrival of the elephantids, which descended from, and slowly replaced, the gomphotheres.[22] The African Primelephas gomphotheroides gave rise to Loxodonta, Mammuthus, and Elephas. Loxodonta branched off earliest around the Miocene and Pliocene boundary while Mammuthus and Elephas diverged later during the early Pliocene. Loxodonta remained in Africa while Mammuthus and Elephas spread to Eurasia, and the former reached North America. At the same time, the stegodontids, another proboscidean group descended from gomphotheres, spread throughout Asia, including the Indian subcontinent, China, southeast Asia, and Japan. Mammutids continued to evolve into new species, such as the American mastodon.[23]

 

At the beginning of the Pleistocene, elephantids experienced a high rate of speciation.[24] The Pleistocene also saw the arrival of Palaeoloxodon namadicus, the largest terrestrial mammal of all time.[25] Loxodonta atlantica became the most common species in northern and southern Africa but was replaced by Elephas iolensis later in the Pleistocene. Only when Elephas disappeared from Africa did Loxodonta become dominant once again, this time in the form of the modern species. Elephas diversified into new species in Asia, such as E. hysudricus and E. platycephus;[26] the latter the likely ancestor of the modern Asian elephant.[24] Mammuthus evolved into several species, including the well-known woolly mammoth.[26] Interbreeding appears to have been common among elephantid species, which in some cases led to species with three ancestral genetic components, such as the Palaeoloxodon antiquus.[7] In the Late Pleistocene, most proboscidean species vanished during the Quaternary glaciation which killed off 50% of genera weighing over 5 kg (11 lb) worldwide.[27]

 

Proboscideans experienced several evolutionary trends, such as an increase in size, which led to many giant species that stood up to 500 cm (16 ft 5 in) tall.[25] As with other megaherbivores, including the extinct sauropod dinosaurs, the large size of elephants likely developed to allow them to survive on vegetation with low nutritional value.[28] Their limbs grew longer and the feet shorter and broader.[6] The feet were originally plantigrade and developed into a digitigrade stance with cushion pads and the sesamoid bone providing support.[29] Early proboscideans developed longer mandibles and smaller craniums while more derived ones developed shorter mandibles, which shifted the head's centre of gravity. The skull grew larger, especially the cranium, while the neck shortened to provide better support for the skull. The increase in size led to the development and elongation of the mobile trunk to provide reach. The number of premolars, incisors and canines decreased.[6]

 

The cheek teeth (molars and premolars) of proboscideans became larger and more specialized, especially after elephants started to switch from C3-plants to C4-grasses, which caused their teeth to undergo a three-fold increase in teeth height as well as substantial multiplication of lamellae after about five million years ago. Only in the last million years or so did they return to a diet mainly consisting of C3 trees and shrubs.[30][31] The upper second incisors grew into tusks, which varied in shape from straight, to curved (either upward or downward), to spiralled, depending on the species. Some proboscideans developed tusks from their lower incisors.[6] Elephants retain certain features from their aquatic ancestry, such as their middle ear anatomy.[32]

 

Several species of proboscideans lived on islands and experienced insular dwarfism. This occurred primarily during the Pleistocene when some elephant populations became isolated by fluctuating sea levels, although dwarf elephants did exist earlier in the Pliocene. These elephants likely grew smaller on islands due to a lack of large or viable predator populations and limited resources. By contrast, small mammals such as rodents develop gigantism in these conditions. Dwarf elephants are known to have lived in Indonesia, the Channel Islands of California, and several islands of the Mediterranean.[33]

Anatomy and morphology

Size

 

African bush elephant skeleton

Elephants are the largest living terrestrial animals. African bush elephants are the largest species, with males being 304–336 cm (10 ft 0 in–11 ft 0 in) tall at the shoulder with a body mass of 5.2–6.9 t (5.7–7.6 short tons) and females standing 247–273 cm (8 ft 1 in–8 ft 11 in) tall at the shoulder with a body mass of 2.6–3.5 t (2.9–3.9 short tons). Male Asian elephants are usually about 261–289 cm (8 ft 7 in–9 ft 6 in) tall at the shoulder and 3.5–4.6 t (3.9–5.1 short tons) whereas females are 228–252 cm (7 ft 6 in–8 ft 3 in) tall at the shoulder and 2.3–3.1 t (2.5–3.4 short tons). African forest elephants are the smallest species, with males usually being around 209–231 cm (6 ft 10 in–7 ft 7 in) tall at the shoulder and 1.7–2.3 t (1.9–2.5 short tons). Male African bush elephants are typically 23% taller than females, whereas male Asian elephants are only around 15% taller than females.[25]

 

Bones

The skeleton of the elephant is made up of 326–351 bones.[34] 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.[35]

 

Head

An elephant's skull is resilient enough to withstand the forces generated by the leverage of the tusks and head-to-head collisions. The back of the skull is flattened and spread out, creating arches that protect the brain in every direction.[36] The skull contains air cavities (sinuses) that reduce the weight of the skull while maintaining overall strength. These cavities give the inside of the skull a honeycomb-like appearance. The cranium is particularly large and provides enough room for the attachment of muscles to support the entire head. The lower jaw is solid and heavy.[34] Because of the size of the head, the neck is relatively short to provide better support.[6] Lacking a lacrimal apparatus, the eye relies on the harderian gland to keep it moist. A durable nictitating membrane protects the eye globe. The animal's field of vision is compromised by the location and limited mobility of the eyes.[37] Elephants are considered dichromats[38] and they can see well in dim light but not in bright light.[39]

 

 

African bush elephant with ears spread in a threat or attentive position; note the visible blood vessels

Ears

Elephant ears have thick bases with thin tips. The ear flaps, or pinnae, contain numerous blood vessels called capillaries. Warm blood flows into the capillaries, helping to release excess body heat into the environment. This occurs when the pinnae are still, and the animal can enhance the effect by flapping them. 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.[40] Elephants are capable of hearing at low frequencies and are most sensitive at 1 kHz (in close proximity to the Soprano C).[41]

 

Trunk

 

African bush elephant with its trunk raised, a behaviour often adopted when trumpeting

 

Asian elephant drinking water with trunk

The trunk, or proboscis, is a fusion of the nose and upper lip, although in early fetal life, the upper lip and trunk are separated.[6] The trunk is elongated and specialised to become the elephant's most important and versatile appendage. It contains up to 150,000 separate muscle fascicles,[42] with no bone and little fat. These paired muscles consist of two major types: superficial (surface) and internal. The former are divided into dorsals, ventrals, and laterals while the latter are divided into transverse and radiating muscles. The muscles of the trunk connect to a bony opening in the skull. The nasal septum is composed of tiny muscle units that stretch horizontally between the nostrils. Cartilage divides the nostrils at the base.[43] As a muscular hydrostat, the trunk moves by precisely coordinated muscle contractions. The muscles work both with and against each other. A unique proboscis nerve – formed by the maxillary and facial nerves – runs along both sides of the trunk.[44]

 

Elephant trunks have multiple functions, including breathing, olfaction, touching, grasping, and sound production.[6] The animal's sense of smell may be four times as sensitive as that of a bloodhound.[45] The trunk's ability to make powerful twisting and coiling movements allows it to collect food, wrestle with other elephants,[46] and lift up to 350 kg (770 lb).[6] It can be used for delicate tasks, such as wiping an eye and checking an orifice,[46] and is capable of cracking a peanut shell without breaking the seed.[6] With its trunk, an elephant can reach items at heights of up to 7 m (23 ft) and dig for water under mud or sand.[46] Individuals may show lateral preference when grasping with their trunks: some prefer to twist them to the left, others to the right.[44] Elephants are capable of dilating their nostrils at a radius of nearly 30%, increasing the nasal volume by 64%, and can inhale at over 150 m/s (490 ft/s) which is around 30 times the speed of a human sneeze.[47] Elephants can suck up food and water both to spray in the mouth and, in the case of the later, to sprinkle on their bodies.[6][47] An adult Asian elephant is capable of holding 8.5 L (2.2 US gal) of water in its trunk.[43] They will also spray dust or grass on themselves.[6] When underwater, the elephant uses its trunk as a snorkel.[32]

 

The African elephant has two finger-like extensions at the tip of the trunk that allow it to grasp and bring food to its mouth. The Asian elephant has only one and relies more on wrapping around a food item and squeezing it into its mouth.[11] Asian elephants have more muscle coordination and can perform more complex tasks.[43] Losing the trunk would be detrimental to an elephant's survival,[6] although in rare cases, individuals have survived with shortened ones. One elephant has been observed to graze by kneeling on its front legs, raising on its hind legs and taking in grass with its lips.[43] Floppy trunk syndrome is a condition of trunk paralysis in African bush elephants caused by the degradation of the peripheral nerves and muscles beginning at the tip.[48]

 

Teeth

 

Closeup of the cheek teeth of a dead juvenile bush elephant

 

Asian elephant eating tree bark, using its tusks to peel it off.

Elephants usually have 26 teeth: the incisors, known as the tusks, 12 deciduous premolars, and 12 molars. Unlike most mammals, which grow baby teeth and then replace them with a single permanent set of adult teeth, elephants are polyphyodonts that have cycles of tooth rotation throughout their lives. The chewing teeth are replaced six times in a typical elephant's lifetime. Teeth are not replaced by new ones emerging from the jaws vertically as in most mammals. Instead, new teeth grow in at the back of the mouth and move forward to push out the old ones. The first chewing tooth on each side of the jaw falls out when the elephant is two to three years old. The second set of chewing teeth falls out at four to six years old. The third set falls out at 9–15 years of age and set four lasts until 18–28 years of age. The fifth set of teeth falls out at the early 40s. The sixth (and usually final) set must last the elephant the rest of its life. Elephant teeth have loop-shaped dental ridges, which are thicker and more diamond-shaped in African elephants.[49]

 

Tusks

The tusks of an elephant are modified second incisors in the upper jaw. They replace deciduous milk teeth at 6–12 months of age and grow continuously at about 17 cm (7 in) a year. A newly developed tusk has a smooth enamel cap that eventually wears off. The dentine is known as ivory and its cross-section consists of crisscrossing line patterns, known as "engine turning", which create diamond-shaped areas. As a piece of living tissue, a tusk is relatively soft; it is as hard as the mineral calcite. Much of the tusk can be seen outside; the rest is in a socket in the skull. At least one-third of the tusk contains the pulp and some have nerves stretching to the tip. Thus it would be difficult to remove it without harming the animal. When removed, ivory begins to dry up and crack if not kept cool and moist. Tusks serve multiple purposes. They are used for digging for water, salt, and roots; debarking or marking trees; and for moving trees and branches when clearing a path. When fighting, they are used to attack and defend, and to protect the trunk.[50]

 

Like humans, who are typically right- or left-handed, elephants are usually right- or left-tusked. The dominant tusk, called the master tusk, is generally more worn down, as it is shorter with a rounder tip. For the 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),[50] but those of males tend to be thicker.[51] In earlier times, elephant tusks weighing over 200 pounds (more than 90 kg) were not uncommon, though it is rare today to see any over 100 pounds (45 kg).[52]

 

In the Asian species, only the males have large tusks. Female Asians have very small tusks, or none at all.[50] Tuskless males exist and are particularly common among Sri Lankan elephants.[53] 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[54] and Asia[55] has led to natural selection for shorter tusks[56][57] and tusklessness.[58][59]

 

Skin

 

An African forest elephant covering its skin with mud

An elephant's skin is generally very tough, at 2.5 cm (1 in) thick on the back and parts of the head. The skin around the mouth, anus, and inside of the ear is considerably thinner. Elephants typically have grey skin, but African elephants look brown or reddish after wallowing in coloured mud. Asian elephants have some patches of depigmentation, particularly on the forehead and ears and the areas around them. Calves have brownish or reddish hair, especially on the head and back. As elephants mature, their hair darkens and becomes sparser, but dense concentrations of hair and bristles remain on the end of the tail as well as the chin, genitals and the areas around the eyes and ear openings. Normally the skin of an Asian elephant is covered with more hair than its African counterpart.[60] Their hair is thought to be for thermoregulation, helping them lose heat in their hot environments.[61]

 

An elephant uses mud as a sunscreen, protecting its skin from ultraviolet light. Although tough, an elephant's skin is very sensitive. Without regular mud baths to protect it from burning, insect bites and moisture loss, an elephant's skin suffers serious damage. After bathing, the elephant will usually use its trunk to blow dust onto its body and this dries into a protective crust. Elephants have difficulty releasing heat through the skin because of their low surface-area-to-volume ratio, which is many times smaller than that of a human. They have even been observed lifting up their legs, presumably in an effort to expose their soles to the air.[60]

 

Legs, locomotion, and posture

 

An Asian elephant walking

To support the animal's weight, an elephant's limbs are positioned more vertically under the body than in most other mammals. The long bones of the limbs have cancellous bone in place of medullary cavities. This strengthens the bones while still allowing haematopoiesis.[62] Both the front and hind limbs can support an elephant's weight, although 60% is borne by the front.[63] Since the limb bones are placed on top of each other and under the body, an elephant can stand still for long periods of time without using much energy. Elephants are incapable of rotating their front legs, as the ulna and radius are fixed in pronation; the "palm" of the manus faces backward.[62] The pronator quadratus and the pronator teres are either reduced or absent.[64] The circular feet of an elephant have soft tissues or "cushion pads" beneath the manus or pes, which distribute the weight of the animal.[63] They appear to have a sesamoid, an extra "toe" similar in placement to a giant panda's extra "thumb", that also helps in weight distribution.[65] As many as five toenails can be found on both the front and hind feet.[11]

 

Elephants can move both forwards and backwards, but cannot trot, jump, or gallop. They use only two gaits when moving on land: the walk and a faster gait similar to running.[62] In walking, the legs act as pendulums, with the hips and shoulders rising and falling while the foot is planted on the ground. With no "aerial phase", the fast gait does not meet all the criteria of running, although the elephant uses its legs much like other running animals, with the hips and shoulders falling and then rising while the feet are on the ground.[66] Fast-moving elephants appear to 'run' with their front legs, but 'walk' with their hind legs and can reach a top speed of 25 km/h (16 mph).[67] At this speed, most other quadrupeds are well into a gallop, even accounting for leg length. Spring-like kinetics could explain the difference between the motion of elephants and other animals.[67] During locomotion, the cushion pads expand and contract, and reduce both the pain and noise that would come from a very heavy animal moving.[63] Elephants are capable swimmers. They have been recorded swimming for up to six hours without touching the bottom, and have travelled as far as 48 km (30 mi) at a stretch and at speeds of up to 2.1 km/h (1 mph).[68]

 

Organs

 

African elephant heart in a jar

The brain of an elephant weighs 4.5–5.5 kg (10–12 lb) compared to 1.6 kg (4 lb) for a human brain. While the elephant brain is larger overall, it is proportionally smaller. At birth, an elephant's brain already weighs 30–40% of its adult weight. The cerebrum and cerebellum are well developed, and the temporal lobes are so large that they bulge out laterally.[69] The throat of an elephant appears to contain a pouch where it can store water for later use.[6] The larynx of the elephant is the largest known among mammals. The vocal folds are long and are attached close to the epiglottis base. When comparing an elephant's vocal folds to those of a human, an elephant's are longer, thicker, and have a larger cross-sectional area. In addition, they are tilted at 45 degrees and positioned more anteriorly than a human's vocal folds.[70]

 

The heart of an elephant weighs 12–21 kg (26–46 lb). It has a double-pointed apex, an unusual trait among mammals.[69] In addition, the ventricles separate near the top of the heart, a trait they share with sirenians.[71] When standing, the elephant's heart beats approximately 30 times per minute. Unlike many other animals, the heart rate speeds up by 8 to 10 beats per minute when the elephant is lying down.[72] The blood vessels in most of the body are wide and thick and can withstand high blood pressures.[71] The lungs are attached to the diaphragm, and breathing relies mainly on the diaphragm rather than the expansion of the ribcage.[69] Connective tissue exists in place of the pleural cavity. This may allow the animal to deal with the pressure differences when its body is underwater and its trunk is breaking the surface for air,[32] although this explanation has been questioned.[73] Another possible function for this adaptation is that it helps the animal suck up water through the trunk.[32] Elephants inhale mostly through the trunk, although some air goes through the mouth. They have a hindgut fermentation system, and their large and small intestines together reach 35 m (115 ft) in length. The majority of an elephant's food intake goes undigested despite the process lasting up to a day.[69]

 

A male elephant's testes are located internally near the kidneys.[74] The elephant's penis can reach a length of 100 cm (39 in) and a diameter of 16 cm (6 in) at the base. It is S-shaped when fully erect and has a Y-shaped orifice. The female has a well-developed clitoris at up to 40 cm (16 in). The vulva is located between the hind legs instead of near the tail as in most mammals. Determining pregnancy status can be difficult due to the animal's large abdominal cavity. The female's mammary glands occupy the space between the front legs, which puts the suckling calf within reach of the female's trunk.[69] Elephants have a unique organ, the temporal gland, located in both sides of the head. This organ is associated with sexual behaviour, and males secrete a fluid from it when in musth.[75] Females have also been observed with secretions from the temporal glands.[45]

 

Body temperature

Elephants are homeotherms, and maintain their average body temperature at ~ 36 °C, with minimum 35.2 °C during cool season, and maximum 38.0 °C during hot dry season.[76] Sweat glands are absent in the elephant's skin, but water diffuses through the skin, allowing cooling by evaporative loss.[77][78][79] Other physiological or behavioral features may assist with thermoregulation such as flapping ears,[80] mud bathing, spraying water on the skin, seeking shade,[76][81] and adopting different walking patterns.[82] In addition, the interconnected crevices in the elephant's skin is thought to impede dehydration and improve thermal regulation over a long period of time.[83]

 

 

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