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18.12.2015 18:17 - Encyclopedia Largest prehistoric animals Vol.1 Vertebrates part1 Mammals ch.19 Armadillos,Glyptodonts and Sloths
Автор: valentint Категория: Забавление   
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Armadillos,Glyptodonts and Sloths (Xenarthra)
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The mammalian order Xenarthra includes the armadillos, sloths and anteaters, and the extinct glyptodonts; the mammalian order Pholidota comprises the pangolins or scaly anteaters. Although they were once thought to be closely related, Xenarthra is now generally considered to represent one of the four primary divisions of placental mammals, with pangolins placed in a separate division. Xenarthrans are united by a suite of unusual anatomical features, primary among them the presence of extra joints in their backbones, whereas pangolin"s most notable feature is their external covering of overlapping, horny scales. Both xenarthrans and pholidotans are typified by adaptations for digging and for feeding on ants and termites, though climbing forms are also common, and sloths and their relatives are herbivorous. Both orders are relatively small, with Xenarthra comprising 31 living species and Pholidota only 8, but Xenarthra also includes a very extensive extinct radiation of highly unusual mammals, including giant herbivorous sloths and the massively armoured, herbivorous glyptodonts.



Armadillos, glyptodonts and pampatheres (
Cingulata)

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1.Panochthus frenzelianus 2.Glyptodon elongatus 3.Doedicurus clavicaudatus

Cingulata,part of the superorder Xenarthra, is an order of armored New World placental mammals. Dasypodids and chlamyphorids, the armadillos, are the only surviving families in the order.Two groups of cingulates much larger than extant armadillos (maximum body mass of 45 kg (100 lb) in the case of the giant armadillo) existed until recently: pampatheriids, which reached weights of up to 200 kg (440 lb) and chlamyphorid glyptodonts, which attained masses of 2,000 kg (4,400 lb) or more.
The cingulate order originated in South America during the Paleocene epoch, and due to the continent"s former isolation remained confined to it during most of the Cenozoic. However, the formation of a land bridge allowed members of all three families to migrate to southern North America during the Pliocene or early Pleistocene as part of the Great American Interchange. After surviving for tens of millions of years, all of the pampatheriids and giant glyptodonts apparently died out during the Quaternary extinction event at the beginning of the Holocene,along with much of the rest of the regional megafauna, shortly after the colonization of the Americas by Paleo-Indians.

The largest
cingulate known is Doedicurus, at 4 meters long. (13 ft).

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Doedicurus clavicaudatus was a prehistoric
glyptodont, living during the Pleistocene until the end of the last glacial period, some 11,000 years ago. This was the largest known glyptodontid, and one of the better-known members of the New World Pleistocene megafauna, with a height of 1.5 meters (5 ft) and an overall length of around 4 meters. Doedicurus could reach a mass of 1,910 to 2,370 kg. It had a huge domed carapace that was made of many tightly fitted scutes, somewhat similar to that of its modern-day relative, the armadillos. Its tail was surrounded by a flexible sheath of bone and had long spikes or knobs on the end, at least in male individuals.
D. clavicaudatus inhabited woodlands and grasslands and was herbivorous. Its tail club was probably used in intraspecific conflict rather than defense against predators like Smilodon unlike the superficially similar club of the Ankylosaurs. For one thing, the latter use would have been difficult since the animal"s field of vision was so limited that it would essentially have had to blindly thrash the tail club. In addition, carapaces have been found which show fractures that were produced by roughly the same amount of energy as could be produced by the tail muscles.
Its name means "pestle tail", referring to how, if the spikes were removed, it would resemble a pestle.
The carapace was firmly anchored to the pelvis but loose around the shoulder. Its front bore an additional smaller dome. This has been interpreted as a fat-filled space, similar to a camel"s hump, which would have stored energy for the dry season and cushioned blows of the tail of rival animals.
Fossils of D. clavicaudatus are found in North America and South America, especially the Ensenada Formation in Argentina.Given the late date of its disappearance, it was encountered and probably also hunted by the first human settlers of South America.


Glyptodon
easily topped 3.3 m (11 ft) and 2 tonnes (4,400 lb).
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Glyptodon (Greek for "grooved or carved tooth") was a large, armored
mammal of the family Glyptodontidae, a relative of armadillos that lived during the Pleistoceneepoch. It was roughly the same size and weight as a Volkswagen Beetle, though flatter in shape. With its rounded, bony shell and squat limbs, it superficially resembled turtles, and the much earlier dinosaurian ankylosaur, as an example of the convergent evolution of unrelated lineages into similar forms. Glyptodon is believed to have been a herbivore, grazing on grasses and other plants found near rivers and small bodies of water.
Glyptodon is part of the superorder of
placental mammals known as Xenarthra. This clade of mammals also includes anteaters, tree sloths, armadillos, and extinctground sloths and pampatheres.
Glyptodon originated in South America. During the Great American Interchange, a set of migrations that occurred after North and South America were connected by the rising of the volcanic Isthmus of Panama, it migrated into Central America as far as Guatemala. A related genus,Glyptotherium,reached the southern region of the modern USA about 2.5 million years ago. They became extinct about 10,000 years ago, probably from over-hunting. The native human population in their range is believed to have hunted them and used the shells of dead animals as shelters in inclement weather.


Panochthus is an extinct genus of glyptodont, which lived in Argentina during the Pleistocene epoch.
imageIt could reach 3 m in length and a weight up to 1500 kg;the upper skull and the body were protected by hemispherical armor composed of hundred of rounded scales. The tail, short and wedge-shaped, consisted of small bony bands with small spikes used for defense.


Anteaters and sloths (
Pilosa)
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The biogeographic origins of the Pilosa are still unclear,but they can be traced back in South America as far as the early Paleogene (about 60 million years ago, only a short time after the end of the dinosaur era). The presence of these animals in Central America and their former presence in North America is a result of the Great American Interchange. A number of sloths were also formerly present on the Antilles, which they reached from South America by some combination of rafting or floating with the prevailing currents.

 


The largest
pilosan ever was Megatherium, a ground sloth with an estimated average weight of 5 tonnes (5.5 tons) and a height of 4 m (13 ft), which is about the same size as the African bush elephant.
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Megatherium  was a
genus of elephant-sized ground sloths endemic to South America that lived from the late Pliocene through the end of the Pleistocene.Its size was exceeded by only a few other land mammals, including mammoths and Paraceratherium
.
The first fossil specimen of Megatherium was discovered in 1788 by Manuel Torres, on the bank of the
Lujбn River in Argentina. The fossil was shipped to Museo Nacional de Ciencias Naturales in Madrid the following year, where it remains. It was reassembled by museum employee Juan Bautista Bru, who also drew the skeleton and some individual bones. Based on Bru"s illustrations, comparative anatomistGeorges Cuvier determined the relationships and appearance of Megatherium. He published his first paper on the subject in 1796, a transcript of a previous lecture at the French Academy of Sciences. He published on the subject again in 1804; this paper was republished in his book Recherches sur les ossemens fossiles de quadrupиdes. In his 1796 paper, Cuvier assigned the fossil the scientific name Megatherium americanum.
Cuvier determined that Megatherium was a sloth, and at first believed that it used its large claws for climbing trees, like modern sloths, although he later changed his hypothesis to support a subterranean lifestyle, with the claws used to dig tunnels.
Fossils of Megatherium and other western megafauna proved popular with the Georgian era public until the discovery of the dinosaurs some decades later. Since the original discovery, numerous other fossil Megatherium skeletons have been discovered across South America, in Chile, Argentina, Bolivia, Peru, Brazil, Paraguay and Uruguay.
Ground sloths are placed within the superorder Xenarthra, a group of South American origin which also includes extinct pampatheres and glyptodonts, as well as living tree sloths, armadillos and anteaters.
The subgenus and species Megatherium (Pseudomegatherium) tarijense appears to be a junior synonym of M. americanum, and merely a small individual.The ground sloths, as with all other xenarthrans, evolved in isolation in South America, while it was an island continent during the Paleogene.
During the Pliocene, the Central American Isthmus formed, causing the Great American Interchange, and a mass extinction of much of the indigenous South American megafauna. Ground sloths were largely unaffected and continued to thrive in spite of competition from the northern immigrants. Ground sloths were among the various South American animal groups to migrate northwards into North America, where they remained and flourished until the late Pleistocene.
The rhinoceros-sized Promegatherium of the Miocene is suggested as the ancestor of Megatherium. The oldest (and smallest) species of Megatherium is M. altiplanicum of Pliocene Bolivia. It was very similar to Promegatherium, and was also about the size of a rhinoceros. M. tarijense has been regarded as a medium-sized Megatherium species, larger than M. altiplanicum, but smaller than M. americanum. It roamed from Bolivia in the Tarija Basin to Peru in the Yantac. Species of Megatherium became larger over time, with the largest species, M. americanum of the late Pleistocene, reaching the size of an African elephant.
Megatherium was one of the largest land
mammals known, weighing up to 4 tonnes and measuring up to 6 m (20 ft) in length from head to tail. It is the largest known ground sloth, as big as modern elephants, and would have only been exceeded in its time by a few species of mammoth. The group is known primarily from its largest species, M. americanum. Megatherium species were members of the abundant Pleistocene megafauna, large mammals that lived during the Pleistocene epoch.
Megatherium had a robust skeleton with a large pelvic girdle and a broad muscular tail. Its large size enabled it to feed at heights unreachable by other contemporary herbivores. Rising on its powerful hind legs and using its tail to form a tripod, Megatherium could support its massive body weight while using the curved claws on its long forelegs to pull down branches with the choicest leaves. This sloth, like a modern anteater, walked on the sides of its feet because its claws prevented it from putting them flat on the ground. Although it was primarily a quadruped, its trackways show that it was capable of bipedal locomotion. Biomechanical analysis also suggests it had adaptations to bipedalism.
Some experts believe that its jaw may have housed a long tongue, which it would use to pull leaves into its mouth, similar to the modern tree sloth. Others question this view. Some of the elements in Megatherium"s oral cavity were fused together: a rigidly articulated stylohyal and epihyal, and the apparatus lies farther anteriorly, which together with the elongated, steeply inclined mandibular symphysis, indicates a relatively shorter geniohyoid muscle and thus more limited capacity for tongue protrusion. It was well adapted for strong, predominantly orthal (up-down) movement for eating rough vegetation. Megatherium possessed the narrowest muzzle of all ground sloths from the Pleistocene. This leads paleobiologists to believe that it was a very selective eater. It had the ability to pick and choose which leaves and twigs it would consume. Megatherium had a large narrow prehensile lip that was capable of grabbing and tearing off particular leaves and twigs and other sorts of vegetation.
Megatherium inhabited
woodland and grassland environments of the lightly wooded areas of South America where it was an endemic species, as recently as 10,000 years ago. Megatherium was adapted to temperate, arid or semiarid open habitats. An example of these most recent finds is at Cueva del Milodon in PatagonianChile. The closely related genus Eremotherium (that has been classified occasionally as part of Megatherium) lived in more tropical environments further north, and invaded temperate North America as part of the Great American Interchange.
The giant ground sloth lived mostly in groups, but it may have lived singly in caves. It probably had mainly a browsing diet in open habitats, but also it probably fed on other moderate to soft tough food. For millions of years, the sloth had no enemies to bother it, so it was probably a diurnal animal.
The giant ground sloth was a herbivore, feeding on leaves such as yuccas, agaves, and grasses. While it fed chiefly on terrestrial plants, it could also stand on its hind legs, using its tail as a balancing tripod, and reach for upper growth vegetation. It would pull itself upright to sit on its haunches or to stand and then tugged at plants with its feet, digging them up with the five sharp claws on each foot. The sloth used its simple teeth to grind down food before swallowing it, and its highly developed cheek muscles helped in this process. The sloth"s stomach was able to digest coarse and fibrous food. It is likely that it spent a lot of time resting to aid digestion.
A recent morpho-functional analysis  indicates that M. americanum was adapted for strong vertical biting. The teeth are hypsodont and bilophodont, and the sagittal section of each loph is triangular with a sharp edge. This suggests that the teeth were used for cutting, rather than grinding, and that hard fibrous food was not the primary dietary component.
While it has been suggested that the giant sloth may have been partly carnivorous, this is a controversial claim. Richard Fariсa and Ernesto Blanco of the Universidad de la Repъblica in Montevideo have analysed a fossil skeleton of M. americanum and discovered that its olecranon - the part of the elbow to which the triceps muscle attaches - was very short. This adaptation is found in carnivores and optimises speed rather than strength. The researchers say this would have enabled M. americanum to use its claws like daggers. They suggest that to add nutrients to its diet, Megatherium may have taken over the kills of Smilodon. Based on the estimated strength and mechanical advantage of its biceps, it has been proposed that Megatherium could have overturned adult glyptodonts (large, armored xenarthrans, related to armadillos) as a means of scavenging or hunting these animals. However, noting that sloths lack the carnassials typical of predators and that traces of bone are absent from the many preserved deposits of sloth dung, Paul Martin has described this proposal as "fanciful".
In the south, the giant ground sloth flourished until about 10,500
radiocarbon years BP. Most cite the appearance of an expanding population of human hunters as the cause of its extinction. There are a few late dates of around 8000 BP and one of 7000 BP for Megatherium remains, but the most recent date viewed as credible is about 10,000 BP. The use of bioclimatic envelope modeling indicates that the area of suitable habitat for Megatherium had shrunk and become fragmented by the mid-Holocene. While this alone would not likely have caused its extinction, it has been cited as a possible contributing factor.
 

Very close contender of size was North American Eremotherium

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At up six meters long Eremotherium rivalled even the world famous Megatherium for size. However unlike Megatherium, Eremotherium fossils are also known in the United States, making Eremotherium one of the largest ground sloths in North America.


Several other sloths grew to large sizes as well, such as
Lestodon,but none as large as Megatherium and Eremotherium
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Megatherium americanum, Eremotherium laurillardi and Lestodon armatus















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Автор: valentint
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