Perception Channels: tactile ; chemical
Other Physical Features: endothermic ; bilateral symmetry
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual
Taxonomy
The mammal order Proboscidea includes just a single family with living representatives, the Elephantidae. Wittemyer (2011) recognized three living elephant species: Asian Elephant (Elephas maximus), African Forest Elephant (Loxodonta cyclotis) and African Savanna Elephant (Loxodonta africana). However, Wittemyer notes that some authorities believe just a single African Elephant species should be recognized, with the forest and savanna forms recognized only as subspecies. African Savanna Elephants are the largest terrestrial animals on Earth.
Morphology
The most distinctive feature of elephantids and their extinct proboscidean relatives is the trunk, which is derived from the nose and upper lip. The African Elephant has two fingerlike projections at the end of its trunk whereas the Asian Elephant has just one. The trunk is very powerful, but also very sensitive and its opposable lips can grasp and manipulate very small items such as single nuts. In addition to manipulating objects, the trunk is also used for breathing, olfaction, touch, and sound production.
The ivory tusks of elephants are enlarged second incisors. Both male and female African Elephants have fully developed tusks, although tusk size varies geographically (in Asian Elephants, only males have fully developed tusks). In some areas, selection from hunting pressure by humans appears to have resulted in decreased average tusk size and an increase in the frequency of tusklessness.
The large ears of African Elephants play an important role in thermoregulation.
African and Asian Elephants differ in numerous ways, including body size, absolute and relative size and shape of ears, tusks, trunk structure, number of ribs, and number of toenails on the front and hind feet. In addition, relative to African Elephants, Asian Elephants tend to have smoother skin and more hair.
Behavior and Ecology
Elephants swim well and are able to submerge themselves and use the trunk as a breathing tube. Among the diverse communication modalities used by elephants is infrasonic communication, which elephants were discovered to utilize only in the late 20th century. The long wavelengths of infrasound are able to travel across large distances, with communication feasible across perhaps as much as 10 km under ideal conditions, although individuals can apparently be distinguished only up to one or a few kilometers. Evidence suggests that seismic signaling may also be used by elephants.
Elephants have a very complex social structure and young animals stay with their mother and her group for many years (perhaps for their entire lives). African Savanna Elephants typically stay within a few meters of their mothers for the first 4-8 years of life. Both Asian and African bulls are typically independent of their families by around 15 years (sometimes as young as six years).
Elephants spend as much as three quarters of their time feeding. Elephants both graze (feeding on grass) and browse (feedingmainly on leaves and terminal twigs of woody plants) and the diet composition may shift dramatically between wet and dry seasons. Asian Elephant diets tend to include more grass than those of African Elephants.
Elephants can thrive in habitats ranging from deserts to rainforests. They play major roles in shaping ecosystems through their consumption of shrubs and trees and as seed dispersers.
In recent times, African Elephants have been distributed from southernmost South Africa to the Sahel. In Roman times, they were present even in the northern Mediterranean region. Today, most African Elephants live in the sub-Saharan savanna and dry woodland ecoregions, but they continue to persist in desert regions such as Mali's Sahel and the Namib. In addition, they are found in dense tropical forests such as those found on East Africa's volcanos. Historically, Asian Elephants occupied a broad range in tropical Asia from Iraq, India, and Sri Lanka to Malaysia, Indonesia, and southern China. Today, they have been extirpated from more than 85% of this range and over 60% of Asian Elephants are thought to reside in India. Other remnant populations are found in Sri Lanka, Burma, Thailand, and the larger islands of the Malay Archpelago.
Elephants and Humans
The lives of elephants and humans have been intertwined for millenia. Asian Elephants were domesticated in the third millenium BC in the Indus Valley and this likely drove the first major declines of the species. Ivory has been a major focus of human-elephant interactions for thousands of years. Given that only the males of Asian Elephants bear tusks, African ivory was needed to satisfy the demand in India, China, and Japan and was being traded by the 6th century BC. The African slave trade was closely tied to the ivory trade, with slaves carrying ivory to the coast, where both were sold. Elephants were eradicated from much of west and southern Africa during this period. With the decline of the slave trade, ivory trade also declined and elephant populations are thought to have rebounded during much of the 1900s. Unfortunately, the 1970s saw a huge upsurge in the ivory trade with a devastating impact. It has been estimated that between 1979 and 1989 the African Elephant population was reduced from around 1.3 million to around half a million. Since then, there have been periods of both recovery and decline and the status of African Elephants remains precarious. As large-scale agriculture has increased in Africa since the 1980s, human-elephant conflicts over crop-raiding have increased. Asian Elephant populations have continued to decline as a result of both the ivory trade and habitat loss/range reduction. Although young elephants can fall prey to Tigers (in Asia) and Lions (in Africa), adult elephants are safe from predators except for humans.
At one time, elephants ranged over much of Africa and southern Asia and into the Middle East. Demand for ivory by the Roman Empire is thought to have led to the eradication of African Elephants from the northern Sahara and Asian Elephants from the Middle East. Elephant populations in both Africa and Asia declined with the increased demand for ivory (notably, for piano keys in the 1800s and 1900s). Range reduction and fragmentation poses a serious threat to the long-term viability of elephant populations in both Africa and Asia. From the vantage point of the early decades of the 21st century, only in southern Africa do elephant populations appear relatively secure, but elephants have shown themselves to be highly adapable and with adequate protection there is still hope for recovery over much of their current range. If the ivory trade increases, this will pose a great threat to remaining elephant populations, especially in light of the political instability in many of the countries in which elephants persist. Counterbalancing these threats, however, is the growing economic importance of ecotourism in many countries with elephants.
(Wittemeyer 2011 and references therein)
The Proboscidea (/ˌprɒbəˈsɪdiə/; from Latin proboscis, from Ancient Greek προβοσκίς (proboskís) 'elephant's trunk') are a taxonomic order of afrotherian mammals containing one living family (Elephantidae) and several extinct families. First described by J. Illiger in 1811, it encompasses the elephants and their close relatives.[1] From the mid-Miocene onwards, most proboscideans were very large. The largest land mammal of all time may have been a proboscidean; Palaeoloxodon namadicus was up to 5.2 m (17.1 ft) at the shoulder and may have weighed up to 22 t (24.3 short tons), almost double the weight of some sauropods like Diplodocus carnegii.[2] The largest extant proboscidean is the African bush elephant, with a record of size of 4 m (13.1 ft) at the shoulder and 10.4 t (11.5 short tons).[2] In addition to their enormous size, later proboscideans are distinguished by tusks and long, muscular trunks, which were less developed or absent in early proboscideans.
Three species of elephant are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. Elephantidae is the only surviving family of the order Proboscidea; extinct members include the mastodons, gomphotheres and stegodonts. The family Elephantidae also contains several extinct groups, including the mammoths and straight-tusked elephants. The distinctive features of proboscideans include a trunk, tusks, and massive legs. Large ear flaps are present in some proboscideans, including elephants. Some also have tough but sensitive skin; others, like the woolly mammoth, have a coat. 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.
Over 180 extinct members of Proboscidea have been described.[3] The earliest proboscideans, Eritherium and Phosphatherium are known from the late Paleocene of Africa.[4] The Eocene included Numidotherium, Moeritherium and Barytherium from Africa. These animals were relatively small and some, like Moeritherium and Barytherium were probably amphibious.[5][6] Later on, genera such as Phiomia and Palaeomastodon arose; the latter likely inhabited more forested areas. Proboscidean diversification changed little during the Oligocene.[5]
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 (mastodons), gomphotheres, amebelodontids (which includes the "shovel tuskers" like Platybelodon), choerolophodontids and stegodontids.[7] Around 10 million years ago, the earliest members of the family Elephantidae emerged in Africa, having originated from gomphotheres.[8] The Late Miocene saw major climactic changes, which resulted in the decline and extinction of many proboscidean groups such as ambelodontids and choerolophodontids.[7] The earliest members of modern genera of Elephantidae appeared during the latest Miocene-early Pliocene around 5 million years ago. The elephantid genera Elephas (which includes the living Asian elephant) and Mammuthus (mammoths) migrated out of Africa during the late Pliocene, around 3.6 to 3.2 million years ago.[9]
Over the course of the Early Pleistocene, all non-elephantid probobscideans outside of the Americas became extinct (including mammutids, gomphotheres and deinotheres), with the exception of Stegodon.[7] Gomphotheres dispersed into South America during this era as part of the Great American interchange,[10] and mammoths migrating into North America around 1.5 million years ago.[11] 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.[12] Proboscideans underwent a dramatic decline during the Late Pleistocene, with all remaining non-elephantid proboscideans (including Stegodon, mastodons, and the 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 around 4,000 years ago.[7][13]
The following cladogram is based on endocasts[14]
Proboscidea Elephantiformes Elephantimorpha Mammutida Elephantoidea Elephantidae PalaeoloxodonProboscideans 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.[15] As with other megaherbivores, including the extinct sauropod dinosaurs, the large size of proboscideans likely developed to allow them to survive on vegetation with low nutritional value.[16] Their limbs grew longer and the feet shorter and broader.[17] The feet were originally plantigrade and developed into a digitigrade stance with cushion pads and the sesamoid bone providing support, with this change developing around the common ancestor of Deinotheriidae and Elephantiformes.[18]
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. The cheek teeth (molars and premolars) became larger and more specialised.[17] In Elephantiformes, the second upper incisor and lower incisor were transformed into ever growing tusks.[19][20] The molar teeth changed from being replaced vertically as in other mammals to being replaced horizontally in the clade Elephantimorpha.[21] While early Elephantimorpha generally had long jaws with well developed lower tusks/incisors, from the Late Miocene onwards, many groups convergently developed brevirostrine (shortened) lower jaws with vestigial or no lower tusks.[22] 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 (hypsodont) and more efficient in consuming grass.[23]
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 proboscideans are known to have lived in Indonesia, the Channel Islands of California, and several islands of the Mediterranean.[24]
Elephas celebensis of Sulawesi is believed to have descended from Elephas planifrons. Elephas falconeri of Malta and Sicily was only 1 m (3 ft), and had probably evolved from the straight-tusked elephant. Other descendants of the straight-tusked elephant existed in Cyprus. Dwarf elephants of uncertain descent lived in Crete, Cyclades and Dodecanese, while dwarf mammoths are known to have lived in Sardinia.[24] The Columbian mammoth colonised the Channel Islands and evolved into the pygmy mammoth. This species reached a height of 1.2–1.8 m (4–6 ft) and weighed 200–2,000 kg (440–4,410 lb). A population of small woolly mammoths survived on Wrangel Island as recently as 4,000 years ago.[24] After their discovery in 1993, they were considered dwarf mammoths.[25] This classification has been re-evaluated and since the Second International Mammoth Conference in 1999, these animals are no longer considered to be true "dwarf mammoths".[26]
Below is an unranked taxonomy of proboscidean genera as of 2019.[27][28][29][30]
{{cite journal}}: CS1 maint: multiple names: authors list (link) {{cite journal}}: CS1 maint: multiple names: authors list (link) The Proboscidea (/ˌprɒbəˈsɪdiə/; from Latin proboscis, from Ancient Greek προβοσκίς (proboskís) 'elephant's trunk') are a taxonomic order of afrotherian mammals containing one living family (Elephantidae) and several extinct families. First described by J. Illiger in 1811, it encompasses the elephants and their close relatives. From the mid-Miocene onwards, most proboscideans were very large. The largest land mammal of all time may have been a proboscidean; Palaeoloxodon namadicus was up to 5.2 m (17.1 ft) at the shoulder and may have weighed up to 22 t (24.3 short tons), almost double the weight of some sauropods like Diplodocus carnegii. The largest extant proboscidean is the African bush elephant, with a record of size of 4 m (13.1 ft) at the shoulder and 10.4 t (11.5 short tons). In addition to their enormous size, later proboscideans are distinguished by tusks and long, muscular trunks, which were less developed or absent in early proboscideans.
Three species of elephant are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. Elephantidae is the only surviving family of the order Proboscidea; extinct members include the mastodons, gomphotheres and stegodonts. The family Elephantidae also contains several extinct groups, including the mammoths and straight-tusked elephants. The distinctive features of proboscideans include a trunk, tusks, and massive legs. Large ear flaps are present in some proboscideans, including elephants. Some also have tough but sensitive skin; others, like the woolly mammoth, have a coat. 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.
