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15.12.2015 14:59 - Encyclopedia Largest Prehistoric Animals Vol.1 Vertebrates part1 Mammals ch.1 Carnivores-Bears,fearisome giants atop the food chain on land
Автор: valentint Категория: Забавление   
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Последна промяна: 18.06 18:53


Attempted extended overview of the largest ever lived animals.Codex consists of collected and processed by me but written by other authors articles. Full overview of vertebrates including the latest paleontological finds. Because of the volume "ve split up. I begin with predatory mammals because these are my favorites.Individual parts are numbered according to their place in the full collection Proceedings in English in order to reach the maximum number of readers.And to preserve the style of the authors.

Опит за разширен обзор на най-големите,живели някога животни.Сборника се състои от събрани и обработени от мен,но написани от други автори статии.Пълен обзор на гръбначните животни,с включване най-новите палеонтологични находки.Заради обема съм го разделил на части.Започвам с хищните бозайници,защото това са моите фаворити.Отделните части са номерирани според мястото си в пълния сборник.

 Bears
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The earliest members of Ursidae belong to the extinct subfamily Amphicynodontinae, including Parictis (late Eocene to early middle Miocene, 38–18 Mya) and the slightly younger Allocyon (early Oligocene, 34–30 Mya), both from North America. These animals looked very different from today"s bears, being small and raccoon-like in overall appearance, with diets perhaps more similar to that of a badger. Parictis does not appear in Eurasia and Africa until the Miocene.It is unclear whether late-Eocene ursids were also present in Eurasia, although faunal exchange across the Bering land bridge may have been possible during a major sea level low stand as early as the late Eocene (about 37 Mya) and continuing into the early Oligocene.European genera morphologically very similar to Allocyon, and to the much younger American Kolponomos (about 18 Mya),are known from the Oligocene, including Amphicticeps and Amphicynodon.There has been various morphological evidence linking amphicynodontines with pinnipeds, as both groups were semi-aquatic, otter-like mammals.In addition to the support of the pinniped–amphicynodontine clade, other morphological and some molecular evidence supports bears being the closet living relatives to pinnipeds.
The raccoon-sized, dog-like Cephalogale is the oldest-known member of the subfamily Hemicyoninae, which first appeared during the middle Oligocene in Eurasia about 30 Mya.The subfamily includes the younger genera Phoberocyon (20–15 Mya), and Plithocyon (15–7 Mya). A Cephalogale-like species gave rise to the genus Ursavus during the early Oligocene (30–28 Mya); this genus proliferated into many species in Asia and is ancestral to all living bears. Species of Ursavus subsequently entered North America, together with Amphicynodon and Cephalogale, during the early Miocene (21–18 Mya). Members of the living lineages of bears diverged from Ursavus between 15 and 20 Mya,likely via the species Ursavus elmensis. Based on genetic and morphological data, the Ailuropodinae (pandas) were the first to diverge from other living bears about 19 Mya, although no fossils of this group have been found before about 5 Mya.
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1. Arctodus 2. Arctotherium 3. Pararctotherium 4. Agriotherium 5. Kretzoiarctos
The New World short-faced bears (Tremarctinae) differentiated from Ursinae following a dispersal event into North America during the mid-Miocene (about 13 Mya).They invaded South America (≈1 Ma) following formation of the Isthmus of Panama.Their earliest fossil representative is Plionarctos in North America (~ 10–2 Ma). This genus is probably the direct ancestor to the North American short-faced bears (genus Arctodus), the South American short-faced bears (Arctotherium), and the spectacled bears, Tremarctos, represented by both an extinct North American species (T. floridanus), and the lone surviving representative of the Tremarctinae, the South American spectacled bear (T. ornatus)
The subfamily Ursinae experienced a dramatic proliferation of taxa about 5.3–4.5 Mya, coincident with major environmental changes; the first members of the genus Ursus appeared around this time.The sloth bear is a modern survivor of one of the earliest lineages to diverge during this radiation event (5.3 Mya); it took on its peculiar morphology, related to its diet of termites and ants, no later than by the early Pleistocene. By 3–4 Mya, the species Ursus minimus appears in the fossil record of Europe; apart from its size, it was nearly identical to today"s Asian black bear. It is likely ancestral to all bears within Ursinae, perhaps aside from the sloth bear. Two lineages evolved from U. minimus: the black bears (including the sun bear, the Asian black bear, and the American black bear); and the brown bears (which includes the polar bear). Modern brown bears evolved from U. minimus via Ursus etruscus, which itself is ancestral to the extinct Pleistocene cave bear. Species of Ursinae have migrated repeatedly into North America from Eurasia as early as 4 Mya during the early Pliocene.


Arctotherium
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The largest terrestrial carnivoran and the largest bear as well as the largest mammalian land-predator of all time was Arctotherium angustidens of the genus Arctotherium or the South American short-faced bears. A humerus of A. angustidens from Buenos Aires indicate that the big males of this species would have weighed 1,588- 1,749 kg and standing at least 11 feet (3.4 meters) tall on the hind-limbs.Arctotherium angustidens was a South-American Short Faced Bear from the genus Arctotherium. It was the largest Carnivoran that ever lived, in most regards; although male southern elephant seals can be heavier, they are semi-aquatic and covered in a layer of blubber.

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A
rctotherium angustidens was the largest Carnivoran that ever lived except that for southern and northern elephant seals. The northern elephant seal was 3,700 kg (8,200 lb) while the southern elephant seal was 5,000 kg (11,000 lb). It weighted about 983–2,042 kg (2,167–4,502 lb) but the authors said it was more likely 1,588 kg (3,501 lb) Arctotherium is an extinct genus of South American short-faced bears within Ursidae of the Pleistocene. Their ancestors migrated from North America to South America during the Great American Interchange, following the formation of the Isthmus of Panama during the late Pliocene. The oldest remains are from the Ensenadan epoch within the early-middle Pleistocene 1.2 Mya. Their closest relatives were the North American short-faced bears of genus Arctodus (A. pristinus and A. simus). The closest living relative would be the spectacled bear (Tremarctos ornatus)
Arctotherium was named by Hermann Burmeister in 1879. It was assigned to Tremarctinae by Krause et al. 2008. A specimen of A. angustidens from Buenos Aires shows an individual estimated, using the humerus, to weigh between 983 and 2,042 kg (2,167 and 4,502 lb), though the authors consider the upper limit as improbable and say that 1,588 kg (3,501 lb) is more likely. It is still possibly the largest bear ever found and contender for the largest carnivorous land mammal known to science. In contrast to their North American relatives, South American short-faced bears showed a trend of declining size and carnivory over time. This has been attributed to increased competition from other, later-arriving or evolving carnivorans, like jaguars, lions or Smilodon populator, following the early dispersal of short-faced bears to South America. (The North American carnivorans that invaded South America, including short-faced bears and Smilodon, quickly dominated the predatory niches formerly occupied by South America"s native metatheriansparassodont and avian phorusrhacid carnivores.)
Species:
Arctotherium angustidens (Gervais & Ameghino, 1880) ,Arctotherium vetustum (Ameghino, 1885) ,Arctotherium wingei (Ameghino, 1902) ,Arctotherium bonariense (Gervais, 1852) ,Arctotherium tarijense (Ameghino, 1902)



North American s
hort-faced bear
(Arctodus)
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Species:
Arctodus simus (Cope, 1879) ,Arctodus pristinus (Leidy, 1854)
The short-faced bear (Arctodus spp.) is an extinct bear that inhabited North America during the Pleistocene epoch from about 1.8 Mya until 11,000 years ago. It was the most common early North American bear and was most abundant in California. There are two recognized species: Arctodus pristinus and Arctodus simus, with the latter considered one of the largest known terrestrial mammalian carnivores.
The name short-faced bear derives from the shape of their skulls, which appear to have a proportionally short snout compared to other bears; this characteristic is also shared by its extant relatives, the spectacled bear and the grizzly bear. However, this apparent shortness is an optical illusion caused by their deep snouts and short nasal regions. The scientific name of the genus, Arctodus, derives from the Greek language and means "bear tooth".
The short-faced bear belongs to a group of bears known as the Tremarctinae, which appeared in the Americas during the earliest parts of the late Miocene epoch in the form of Plionarctos, a genus considered ancestral to Arctodus, Arctotherium and the modern spectacled bear (Tremarctos ornatus). Although the early history of Arctodus is poorly known, it evidently became widespread in North America by the Kansan age about 800,000 years ago.
Arctodus simus first appeared during the middle Pleistocene in North America, about 800,000 years ago, ranging from Alaska to Mississippi, and it became extinct about 11,600 years ago. Its fossils were first found in the Potter Creek Cave, Shasta County, California. It might have been the largest carnivorous land mammal that ever lived in North America. Only one Giant Short-faced Bear skeleton has been found in Indiana, unearthed south of Rochester on west of Nyona Lake on Chet Williams" farm. It has become well known in scientific circles because it was the biggest most-nearly complete skeleton of a giant short-faced bear found in America. The original bones are in the Field Museum, Chicago. The new Indiana State Museum, Indianapolis, and the Yukon Beringia Interpretive Centre, Whitehorse, Yukon Territory, Canada, have casts made of the bones. In a recent study, the mass of six specimens was estimated, one-third of them weighed about 900 kg (1 short ton), the largest being UVP 015 at 957 kg (2,110 lb), suggesting specimens that big were probably more common than previously thought. It stood 8–10 feet (2.4–3.0 m) tall on hind legs while a large specimen would have been 11–12 feet (3.4–3.7 m) tall with a 14 foot (4.3 m) vertical arm reach, and 5–6 feet (1.5–1.8 m) high at the shoulder when walking on all fours, it was tall enough to look a man in the eye. At Riverbluff Cave, Missouri, a series of claw marks up to 15 feet (4.57 m) high have been found along the cave wall indicating Short-faced bears over 12 feet (3.65 m) tall.
Arctodus pristinus inhabited more southerly areas, ranging from northern Texas to New Jersey in the east, Aguascalientes, Mexico to the southwest, and with large concentrations in Florida, the oldest from the Santa Fe River 1 site of Gilchrist County, Florida paleontological sites.
Researchers disagree on the diet of Arctodus. Analysis of their bones showed high concentrations of nitrogen-15, a stable nitrogen isotope accumulated by meat-eaters, with no evidence of ingestion of vegetation. Based on this evidence, A. simus was highly carnivorous and as an adult would have required 16 kg (35.3 lb) of flesh per day to survive.
One theory of its predatory habits envisages A. simus as a brutish predator that overwhelmed the large mammals of the Pleistocene with its great physical strength. However, despite being very large, its limbs were too gracile for such an attack strategy. Alternatively, long legs and speed (50–70 km/h (30–40 mph)) may have allowed it to run down Pleistocene herbivores, such as wild horses and saiga antelopes, in a cheetah-like fashion. However, in this scenario, the bear’s sheer physical mass would be a handicap. Arctodus skeletons do not articulate in a way that would have allowed for quick turns, an ability required of any predator that survives by killing agile prey. Paul Matheus, paleontologist at the University of Alaska Fairbanks, determined that Arctodus" moved in a pacing motion like a camel, horse, and modern bears, making it built more for endurance than for great speed. A. simus, according to these arguments, was ill-equipped to be an active predator, leading some to conclude that it was a kleptoparasite, using its enormous size to intimidate smaller predators, such as dire wolves, Smilodon, and American lions, from their kills.
Some authors also suggest that the giant short-faced bear and the cave bear were omnivores, like most modern bears, and the former may have eaten plants depending on availability.
 

Ursus maritimus tyrannus

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Ursus maritimus tyrannus was a very large fossil subspecies of the polar bear that descended from an Arctic population of brown bears. Its name in Latin means Tyrant Sea Bear.
Ursus maritimus tyrannus was the first polar bear and evolved sometime in the mid-Pleistocene. While the oldest fossil is 100,000 years old, they are thought to have evolved between 100,000 and 250,000 years ago from a population of brown bears likely isolated by glaciation. That population is believed to have diminished in numbers quickly into a much smaller population selected by species individual variation who adapted better to the changed environment. Over time with intense selective pressures on a small population they evolved the characteristics of the first polar bears.
Initially the isolated brown bears were no different than the variations of brown bears of that time period. Because litters of cubs can show significant species variations in hair color and hair thickness, this gave certain individuals a survival advantage passed on each generation. Eventually skull changes and even changes in dentition occurred leading to the smooth and rather quick evolution of U. maritimus tyrannus.
U. maritimus tyrannus was considerably larger then its modern relative. If everything is scaled out correctly from its remains, it would had been 183 cm (6 ft) at the shoulders, 3,6 m (12 ft) long and would have weighted an average of 1.2 tons, making it the largest bear "and one of the largest mammalian carnivores to ever walk on land". Its tremendous size makes it even bigger than the other "largest" mammalian carnivores that ever lived, including Andrewsarchus, Agriotherium, and Arctodus simus. It"s speculated that this gigantic bear would, due to its formidable size and strength, have preyed on mammoths which also lived during the time


Ursus arctos priscus - Pleistocene brown bear
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In Eurasia during the Pleistocene, the brown bears described are assigned the subspecies Ursus arctos priscus, and were larger than those in the area today in dimensions: length - 2,9 m, height - 140-170 сm, weight - 600-1000 kg.
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From the beginning of the first scientific explorations of caves, the Zoolithenhцhle in Franconia, Germany, was famous for its rich fossil content. In addition to the numerous remains of cave bears and other animals, a skull of a clearly distinct kind of bear was found, originally called Ursus priscus GOLDFUSS, 1818. Three years later, the term Ursus fossilis was introduced along with a published description of the skull, which led to confusion about the adequate designation of the new species. U. priscus was regarded as a contemporary of the cave bear, i.e. Late Pleistocene in age, but the geological age of the find is still unclear even today, and from the overall state of preservation it could be even of Holocene age.  The specimen probably represents a female individual. A revised study of the skull demonstrates that it is identical to modern U. arctos.On the basis of this evidence, U. priscus, U. fossilis and its synonyms are invalid terms.The nature of Late Pleistocene brown bears is still not well known. In Beringia, brown bears exhibited lower N15 values than today, and than that of short-faced bears, as a result of competitive exclusion for meat.
Consequently, they were likely more herbivorous than today, as an adaptation to competition with the larger Arctodus. This is similar to the situation between modern grizzlies and black bears, but in this case, the grizzly was the underdog.
After 20kya,  around the time of the giant bear"s decline, brown bears appear to have shifted their diets to include more meat, likely due to the large absence of the larger short-faced bear.
In Europe, the opposite was true. The highly herbivorous cave bears overlapped with their cousins in many parts of Europe, and where they did, brown bears had to maintain higher N15 values, in order to adapt to competition for plant resources.
In other words, they were more carnivorous than today, making them possibly the largest predator on the mammoth steppe. This changes after the extinction of cave bears, where they shift to a more generalised diet.





 

 

 








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Автор: valentint
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