Proboscidea

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Proboscidea
Temporal range: Middle Paleocene-Holocene 60.0–0  Ma
Elephant Diversity.jpg
Proboscidean diversity: Indian elephant, Elephas maximus indicus , African bush elephant, Loxodonta africana and African forest elephant, Loxodonta cyclotis
Moeritherium sp.jpg
Skeleton of Moeritherium
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Mirorder: Tethytheria
Order: Proboscidea
Illiger, 1811
Subclades

Proboscidea ( /ˌprɒbəˈsɪdiə/ ; from Latin proboscis , from Ancient Greek προβοσκίς (proboskís) 'elephant's trunk') is 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] Three species of elephant are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant.

Extinct members of Proboscidea include the deinotheres, mastodons, gomphotheres and stegodonts. The family Elephantidae also contains several extinct groups, including mammoths and Palaeoloxodon . Proboscideans include some of the largest known land mammals. The largest land mammal of all time may have been a proboscidean; the elephant Palaeoloxodon namadicus has been estimated to be up to 5.2 m (17.1 ft) at the shoulder and may have weighed up to 22 t (24.3 short tons), surpassing the paraceratheres, the otherwise largest known land mammals, though this estimate was made based on a single fragmentary femur and is speculative. [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.

Evolution

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]

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 climatic changes, which resulted in the decline and extinction of many proboscidean groups such as amebelodontids and choerolophodontids. [7] The earliest members of modern genera of Elephantidae appeared during the latest Miocene-early Pliocene around 6-5 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] By the beginning of the Late Pleistocene, proboscideans were represented by around 23 species. Proboscideans underwent a dramatic decline during the Late Pleistocene as part of the Late Pleistocene megafauna extinctions, 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 around 4,000 years ago. [7] [13]

The following cladogram is based on endocasts [14]

Proboscidea
"plesielephantiforms"
"mastodonts"

Morphology

Over the course of their evolution, proboscideans experienced a significant increase in body size. Some members of the families Deinotheriidae, Mammutidae, Stegodontidae and Elephantidae are thought to have exceeded modern elephants in size, with shoulder heights over 4 metres (13 ft) and masses over 10 tonnes (22,000 lb). [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] Members of Elephantiformes which have retracted nasal regions of the skull indicating the development of a trunk, as well as well-developed tusks on the upper and lower jaws. [19]

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. [20] [21] The tusks are proportionally heavy for their size, being primarily composed of dentine. In primitive proboscideans, a band of enamel covers part of the tusk surface, though in many later groups including modern elephants the band is lost, with elephants only having enamel on the tusk tips of juveniles. The upper tusks were initially modest in size, but from the Late Miocene onwards proboscideans developed increasingly large tusks, with the longest ever recorded tusk being 5.02 metres (16.5 ft) long belonging to the mammutid "Mammut" borsoni found in Greece, with some mammoth tusks likely weighing over 200 kilograms (440 lb). The lower tusks are generally smaller than the upper tusks, but could grow to large sizes in some species, like in Deinotherium (which lacks upper tusks), where they could grow over 1.5 metres (4.9 ft) long, the amebelodontid Konobelodon has lower tusks 1.61 metres (5.3 ft) long, with the longest lower tusks ever recorded being from the primitive elephantid Stegotetrabelodon which are around 2.2 metres (7.2 ft) long. [22]

The molar teeth changed from being replaced vertically as in other mammals to being replaced horizontally in the clade Elephantimorpha. [23] While early Elephantimorpha generally had lower jaws with an elongated mandibular symphysis at the front of the jaw 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. [24] [25] Elephantids are distinguished from other 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. [26]

Dwarfism

Skeleton of Palaeoloxodon falconeri, one of the smallest known dwarf elephants, with an adult shoulder height less than 1 metre (3.3 ft) Pair of Sicilian elephants, skeletons, Elephas Falconeri, AM Syracuse, 121264.jpg
Skeleton of Palaeoloxodon falconeri , one of the smallest known dwarf elephants, with an adult shoulder height less than 1 metre (3.3 ft)

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. [27]

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. [27] 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. [27] After their discovery in 1993, they were considered dwarf mammoths. [28] 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". [29]

Ecology

It has been suggested that members of Elephantimorpha, including mammutids, [30] gomphotheres, [31] and stegodontids, [32] lived in herds like modern elephants. Analysis of remains of the American mastodon (Mammut americanum) suggest that like modern elephants, that herds consisted of females and juveniles and that adult males lived solitarily or in small groups, and that adult males periodically engaged in fights with other males during periods similar to musth found in living elephants. These traits are suggested to be inherited from the last common ancestor of mammutids and elephantids, [30] with musth-like behaviour also suggested to have occurred in gomphotheres. [33] All elephantimorphs are suggested to have been capable of communication via infrasound, as found in living elephants. [34]

Classification

Below is an unranked taxonomy of proboscidean genera as of 2019. [35] [36] [37] [38]

Related Research Articles

<span class="mw-page-title-main">Mammoth</span> Extinct genus of mammals

A mammoth is any species of the extinct elephantid genus Mammuthus. They lived from the late Miocene epoch into the Holocene about 4,000 years ago, and various species existed in Africa, Europe, Asia, and North America. Mammoths are more closely related to living Asian elephants than African elephants.

<span class="mw-page-title-main">Elephantidae</span> Family of mammals

Elephantidae is a family of large, herbivorous proboscidean mammals collectively called elephants and mammoths. These are large terrestrial mammals with a snout modified into a trunk and teeth modified into tusks. Most genera and species in the family are extinct. Only two genera, Loxodonta and Elephas, are living.

<span class="mw-page-title-main">Mammutidae</span> Extinct family of mammals

Mammutidae is an extinct family of proboscideans belonging to Elephantimorpha. It is best known for the mastodons, which inhabited North America from the Late Miocene until their extinction at beginning of the Holocene, around 11,000 years ago. The earliest fossils of the group are known from the Late Oligocene of Africa, around 24 million years ago, and fossils of the group have also been found across Eurasia. The name "mastodon" derives from Greek, μαστός "nipple" and ὀδούς "tooth", referring to their characteristic teeth.

<i>Elephas</i> Genus of mammals

Elephas is one of two surviving genera in the family of elephants, Elephantidae, with one surviving species, the Asian elephant, Elephas maximus. Several extinct species have been identified as belonging to the genus, extending back to the Pliocene era.

<i>Palaeoloxodon</i> Genus of extinct elephants

Palaeoloxodon is an extinct genus of elephant. The genus originated in Africa during the Early Pleistocene, and expanded into Eurasia at the beginning of the Middle Pleistocene. The genus contains some of the largest known species of elephants, over 4 metres (13 ft) tall at the shoulders, including the African Palaeoloxodon recki, the European straight-tusked elephant and the South Asian Palaeoloxodon namadicus. P. namadicus has been suggested to be the largest known land mammal by some authors based on extrapolation from fragmentary remains, though these estimates are highly speculative. In contrast, the genus also contains many species of dwarf elephants that evolved via insular dwarfism on islands in the Mediterranean, some only 1 metre (3.3 ft) in height, making them the smallest elephants known. The genus has a long and complex taxonomic history, and at various times, it has been considered to belong to Loxodonta or Elephas, but today is usually considered a valid and separate genus in its own right.

<i>Stegodon</i> Genus of extinct proboscidean

Stegodon is an extinct genus of proboscidean, related to elephants. It was originally assigned to the family Elephantidae along with modern elephants but is now placed in the extinct family Stegodontidae. Like elephants, Stegodon had teeth with plate-like lophs that are different from those of more primitive proboscideans like gomphotheres and mammutids. The oldest fossils of the genus are found in Late Miocene strata in Asia, likely originating from the more archaic Stegolophodon, subsequently migrating into Africa. While the genus became extinct in Africa during the Pliocene, Stegodon remained widespread in South, Southeast and East Asia until the end of the Pleistocene.

<span class="mw-page-title-main">Gomphothere</span> Extinct family of proboscidean mammals

Gomphotheres are an extinct group of proboscideans related to modern elephants. They were widespread across Afro-Eurasia and North America during the Miocene and Pliocene epochs and dispersed into South America during the Pleistocene as part of the Great American Interchange. Gomphotheres are a paraphyletic group that is ancestral to Elephantidae, which contains modern elephants, as well as Stegodontidae. While most famous forms such as Gomphotherium had long lower jaws with tusks, which is the ancestral condition for the group, some later members developed shortened (brevirostrine) lower jaws with either vestigial or no lower tusks, looking very similar to modern elephants, an example of parallel evolution, which outlasted the long-jawed gomphotheres. By the end of the Early Pleistocene, gomphotheres became extinct in Afro-Eurasia, with the last two genera, Cuvieronius ranging from southern North America to western South America, and Notiomastodon having a wide range over most of South America until the end of the Pleistocene around 12,000 years ago, when they became extinct following the arrival of humans.

<i>Gomphotherium</i> Extinct genus of elephant-like mammals

Gomphotherium is an extinct genus of gomphothere proboscidean from the Neogene of Eurasia, Africa and North America. The genus is probably paraphyletic.

<i>Anancus</i> Genus of proboscideans

Anancus is an extinct genus of "tetralophodont gomphothere" native to Afro-Eurasia, that lived from the Tortonian stage of the late Miocene until its extinction during the Early Pleistocene, roughly from 8.5–2 million years ago.

<i>Cuvieronius</i> Extinct genus of mammals

Cuvieronius is an extinct New World genus of gomphothere which ranged from southern North America to western South America during the Pleistocene epoch. Among the last gomphotheres, it became extinct at the end of the Pleistocene, approximately 12,000 years ago, following the arrival of humans to the Americas.

<span class="mw-page-title-main">Steppe mammoth</span> Extinct species of mammal

Mammuthus trogontherii, sometimes called the steppe mammoth, is an extinct species of mammoth that ranged over most of northern Eurasia during the Early and Middle Pleistocene, approximately 1.7 million-200,000 years ago. One of the largest mammoth species, it evolved in East Asia during the Early Pleistocene, around 1.8 million years ago, before migrating into North America around 1.5 million years ago, and into Europe during the Early/Middle Pleistocene transition, around 1 to 0.7 million years ago. It was the ancestor of the woolly mammoth and Columbian mammoth of the later Pleistocene.

<i>Sinomastodon</i> Extinct genus of gomphothere proboscidean

Sinomastodon is an extinct gomphothere genus known from the Late Miocene to Early Pleistocene of Asia, including China, Japan, Thailand, Myanmar, Indonesia and probably Kashmir.

<i>Tetralophodon</i> Extinct genus of mammals

Tetralophodon is an extinct genus of "tetralophodont gomphothere" belonging to the superfamily Elephantoidea, known from the Miocene of Afro-Eurasia.

Primelephas is a genus of Elephantinae that existed during the Miocene and Pliocene epochs. The name of the genus suggests 'first elephant'. These primitive elephantids are thought to be the common ancestor of Mammuthus, the mammoths, and the closely allied genera Elephas and Loxodonta, the Asian and African elephants, diverging some 4-6 million years ago. It had four tusks, which is a trait not shared with its descendants, but common in earlier proboscideans. The type species, Primelephas gomphotheroides, was described by Vincent Maglio in 1970, with the specific epithet indicating the fossil specimens were gomphothere-like. Primelephas korotorensis is the only other species to be assigned to the genus. All fossils found of the Primelephas have been found in Africa, primarily in modern day Chad, Tanzania, Kenya, Ethiopia, and Uganda.

<i>Eubelodon</i> Extinct genus of proboscid

Eubelodon is an extinct genus of gomphothere which lived in North America during the Miocene Epoch. It contains a single species: Eubelodon morrilli.

<i>Notiomastodon</i> Extinct genus of mammals

Notiomastodon is an extinct genus of gomphothere proboscidean, endemic to South America from the Pleistocene to the beginning of the Holocene. Notiomastodon specimens reached a size similar to that of the modern Asian elephant. Like other brevirostrine gomphotheres such as Cuvieronius and Stegomastodon, Notiomastodon had a shortened lower jaw and lacked lower tusks, unlike more primitive gomphotheres like Gomphotherium.

<span class="mw-page-title-main">Stegodontidae</span> Family of extinct elephant-like mammals

Stegodontidae is an extinct family of proboscideans from Africa and Asia from the Early Miocene to the Late Pleistocene. It contains two genera, the earlier Stegolophodon, known from the Miocene of Asia and the later Stegodon, from the Late Miocene to Late Pleistocene of Africa and Asia which is thought to have evolved from the former. The group is noted for their plate-like lophs on their teeth, which are similar to elephants and different from those of other extinct proboscideans like gomphotheres and mammutids, with both groups having a proal jaw movement utilizing forward strokes of the lower jaw. These similarities with modern elephants were probably convergently evolved. Like elephantids, stegodontids are thought to have evolved from gomphothere ancestors.

<span class="mw-page-title-main">Amebelodontidae</span> Extinct family of mammals

Amebelodontidae is an extinct family of large herbivorous proboscidean mammals related to elephants. They were formerly assigned to Gomphotheriidae, but recent authors consider them a distinct family. They are distinguished from other proboscideans by having flattened lower tusks and very elongate mandibular symphysis. The lower tusks could grow considerable size, with those of Konobelodon reaching 1.61 metres (5.3 ft) in length. Their molar teeth are typically trilophodont, and possessed posttrite conules. In the past, amebelodonts' shovel-like mandibular tusks led to them being portrayed scooping up water plants, however, dental microwear suggests that they were browsers and mixed feeders. The lower tusks have been proposed to have had a variety of functions depending on the species, including stripping bark, cutting through vegetation, as well as possibly digging. They first appeared in Africa during the Early Miocene, and subsequently dispersed into Eurasia and then North America. They became extinct by the beginning of the Pliocene. While some phylogenetic studies have recovered Amebelodontidae as a monophyletic group that forms the sister group to Gomphotheriidae proper, some authors have argued that Amebelodontidae may be polyphyletic, with it being suggested that the shovel-tusked condition arose several times independently within Gomphotheriidae, thus rendering the family invalid.

<span class="mw-page-title-main">Choerolophodontidae</span> Extinct family of mammals

Choerolophodontidae is an extinct family of large herbivorous mammals that were closely related to elephants. Two genera are known, Afrochoerodon and Choerolophodon.

Eurybelodon is an extinct genus of proboscidean in the family Amebelodontidae. It lived in the Clarendonian age of the Miocene.

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