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15.12.2015 15:06 - Encyclopedia Largest prehistoric animals Vol.1 Vertebrates part1 Mammals ch.1 Carnivores-Giant prehistoric bears,sequel
Автор: valentint Категория: Забавление   
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Cave bear- Ursus spelaeus

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Ursus spelaeus, better known as the cave bear is by far one of the most common Pleistocene mammals in the fossil record, thanks mainly due to its behaviour of frequenting caves. In fact the fossils of Ursus spelaeus are so numerous that in World War I the German army used them as a source of phosphates.
The huge numbers of cave bear fossils in caves that have been documented to represent thousands of individuals to a single cave strongly suggests that this bear regularly spent time in caves, perhaps returning to rest after foraging. Bears that we know today by contrast only frequent caves during the hibernation period and sleep outdoors during the warmer months. The immense number of Ursus spelaeus fossils in certain caves has also led to the theory that these bears may have actually lived in social groups, although in depth study of the layers and dating has suggested that the remains are of single individual bears building up over the course of the Pleistocene period. As older remains became buried by sediment and fossilised they would have been of no nutritional value to anything and would have been left alone to accumulate, giving the impression of several bears living together rather than just one or two.
Cave bears have long been thought to be herbivorous animals, meaning that they only ate plants. Key evidence for this comes from the lack of premolar teeth that are usually absent in herbivores resulting in a gap between the forwards canines and rear molars called a diastema. Isotope analysis has also yielded low amounts of carbon-13 and nitrogen-15 which are usually found in high concentrations in carnivores. Counter to the strictly herbivorous diet theory however is the presence of some fossils that do have elevated levels of nitrogen-15, as, well as tooth wear associated with the gnawing of bones. Additionally some cave bear fossils also have tooth marks on them that seem to have been caused by others of their species. Not only does this suggest that cave bears occasionally ate meat, they may have scavenged the dead bodies of other cave bears that had died in caves. This is why Ursus spelaeus is today considered by most to have been an opportunistic omnivore that relied mostly upon eating plants, but would also supplement its diet with occasional meat when it was able to.
As one might expect cave bears were most common in areas that had large amounts of caves, particularly limestone that would have had caves carved out by water over several eons. As such cave bears lived in ecosystems that were between lowland plains and high level mountains that would have had a greater variety of trees and vegetation growing in them. Aside from offering a greater variety of food, a habitat preference such as this suggests that Ursus spelaeus did not compete with other European megafauna such as the woolly rhino and the woolly mammoth since they inhabited more open areas. Cave bears could also range across most of Europe, settling where they encountered suitable habitats, because the lower sea levels meant that marine boundaries such as the English Channel and North Sea did not exist.
A greater determining factor in the range of cave bears was the amount of glacial cover, something that would have expanded and receded over varying periods. Ursus spelaeus individuals from both milder and harsher times are known, with the individuals present in harsher times growing slightly larger than the bears that lived in slightly warmer times. This is a simple strategy where growing bigger creates a greater level of outer insulation while the total surface area of the body still increases but at proportionately less amount than the total body mass. This has been repeated and documented many times for different mammals that live in colder climates that all grow proportionately bigger that their closest related genera, perhaps the most relevant example here being the polar bear (Ursus maritimus) which does well in arctic conditions, but has been seen to overheat when kept in zoos in warmer climates.
Returning to the large collections of remains mentioned above, it’s clear that large numbers of Ursus spelaeus died in caves, but this needs further investigation. Because the remains of cave bears accumulated over tens of thousands of years it is easy to immediately discount the possibility of cave ins, as such an event would have only trapped one bear and then prevented others from entering. One widely accepted theory is that cave bears that did not eat enough food during the summer months to build up their fat reserves ended up starving to death as they slumbered. Even today animals that rely upon hibernation to last out the colder winter are vulnerable in times where plants do not grow or produce as much sustenance as they usually do, and back in the Pleistocene when ice sheets were toing and froing across Europe food would have been even more unpredictable from year to year.
More in depth study of some cave bear remains has revealed that bone disorders such as rickets, periostitus and osteomyelitis were quite common including other ailments such as the presence of tumours. Although not necessarily fatal to the individuals these bones belonged to, they would have impeded their ability to forage, slowly bringing the animal down to the point where it could no longer support itself. In these weakened states its thought that cave bears may have even fallen as prey to cave hyenas as well as even the European cave lion, that otherwise may have given a healthy bear in the prime of its life a wide birth.
Ultimately as a species, cave bears seem to have succumbed to the effects of habitat loss, as by only living in caves these bears would have only ever had a set amount of areas available to them. However as the Pleistocene was reaching its final stages, Neanderthals were beginning to become more common, and these primitive people also used caves for shelter. Inevitably one species would have to give way, and it was the cave bear that lost out to the greater numbers and intelligence of Neanderthals.
However despite the fact that they seem to have taken over, Neanderthals also seem to have held cave bears in very high regard. There are several burial sites in Europe where the remains of several bears have been assembled in pits and then covered with stone slabs. Perhaps the most famous site is Drachenloch, Switzerland where seven cave bear skulls are arranged to face the front of the cave, while six more are placed in recessed notches in the cave wall further in. Further remains were found bundled together, along with a skull of a three year old juvenile bear that had had its cheek pierced by the leg bone of another juvenile bear. Although some researchers claim that these are natural occurrences, there are a great many other who believe that remains like these are those of an ancient bear cult. How and why bears would be worshipped is uncertain, but it could be for anything from a totem animal, to a guardian of the caves against intruders, to maybe even a ward against other cave bears wandering in to Neanderthal settlements.


Ursus deningeri
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Ursus deningeri (Deninger"s bear) is an extinct species of mammal of the family Ursidae (bears), endemic to Eurasia during the Pleistocene for approximately 1.7 million years, from ~1.8 Mya to 100,000 years ago. This large contemporary with the Cave Bear is reached sizes from 2.5 meters to length , 1.4 meters in height at the withers and weigh up to 600 kilograms.The range of this bear has been found to encompass both Europe and Asia, demonstrating the ability of the species to adapt to many Pleistocene environments. U. deningeri is a descendant of U. savini and an ancestor of U. spelaeus.
Ursus deningeri has a combination of primitive and derived characters that distinguishes it from all other Pleistocene bears. Its mandible is slender like that of living brown bears and Ursus etruscus. It also has derived characters of cave bears (Ursus spelaeus) and is considered to be the descendant of Ursus savini and very close to the common ancestor of brown bears.


Ursus ingressus
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This large contemporary with the Cave Bear is reached sizes from 2.3 meters to length , 1.3 meters in height at the withers and weigh up to 350 kilograms.
Whereas U. spelaeus inhabited mainly low and medium elevation areas, U. ingressus has mostly been found in medium and high elevated regions . Recent isotopic analyses showed also some dietary differentiation between these cave bear haplogroups. Ursus ingressus was likely better adapted to continental environments and, thus, might have outperformed U. spelaeus during cold and arid climate conditions.
The vast majority of fossil remains in Late Pleistocene deposits from Niedźwiedzia Cave in Kletno, Sudetes, Poland, belong to the cave bear. Phylogenetic analyses based on a fragment of the mitochondrial D-loop region extracted from two cave bear samples unambiguously showed their close relationship with the Ursus ingressus haplogroup. This taxonomic affiliation of the cave bear remains from Niedźwiedzia Cave was further confirmed by biometrical analyses of molar teeth and skulls. Our results represent the first record of U. ingressus north of the Carpathian Arch, while radiocarbon dating (> 49,000 yr BP) of the samples indicates that they represent some of the oldest specimens of this cave bear taxon known so far. Multi-method phylogenetic analyses including numerous publicly available cave bear sequences allowed analysing the relationships among these samples in details, including the significance of particular clades, and discussing some aspects of cave bear phylogeography. The sequences of U. ingressus from Poland are most closely related to specimens from the Ural Mountains and next to Slovenia, which may indicate migrations between Central and Eastern European populations. The internal placement of Ural.  


Florida cave bear -
Tremarctos floridanus

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Tremarctos floridanus occasionally called the Florida spectacled bear, Florida cave bear, or rarely Florida short-faced bear, is an extinct species of bear in the family Ursidae,subfamily Tremarctinae. T. floridanus was endemic to North America from the Pliocene to Holocene epoch (4.9 million — 11,000 years ago), existing for approximately 4.9 million years.Tremarctos floridanus
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This smaller contemporary giantess bears Arktodus and Arctotherium weighed up to 450-500 kg.

T. floridanus was widely distributed south of the continental ice sheet, along the Gulf Coast across through Florida and north to Tennessee, and across the southern United States to California.
Arctodus (3 million — 11,000 years ago) was a contemporary and shared its habitat with T. floridanus. The closest living relative of the Florida cave bear is the spectacled bear of South America; they are classified together with the huge short-faced bears in the subfamilyTremarctinae. They became extinct at the end of the last ice age, 10,000 years ago (possibly as late as 8,000 years ago at Devil"s Den in Florida), due to some combination of climate change and hunting by newly arrived Paleo-Indians.


Agriotherium
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Agriotherium size is
approximately 2.7 meters long and up to around 650 kilograms.
Another thing to consider is that if Agriotherium was a scavenger then it was likely getting to carcasses after all of the choice pieces of meat had been consumed with perhaps only bones being left. This would probably not be enough to thwart Agriotherium from a meal however since the short snout, strong jaw closing muscles and robust construction of the skull and jaws were all the things that Agriotherium needed to develop massive bite force. Computer modelling in a 2012 study (see links below) confirmed that Agriotherium had one of the largest bite forces known amongst the members of the Carnivora (A group of mammals that includes dogs, bears, cats, pinnipeds etc which are specially adapted to exist by eating meat). By being able to crack open bones, Agriotherium could access and eat the bone marrow within, and for those not familiar, bone marrow is one of the most nutritious parts of an animal, and can last for several years after an animals death when encased inside of the bones. One of the better known bears in the worlds fossil record, the Agriotherium genus is also easily one of the largest currently known. With this large size it would be tempting to portray Agriotherium as a savage killers of any animal that might be unfortunate enough to be in its way, yet like with its more famous relative Arctodus (better known as the giant short faced bear) first impressions may in this case be deceptive. The post cranial skeleton of Agriotherium is that of a large but relatively underpowered animal that simply does not seem to have the skeletal framework necessary to cope with high stresses, such as those expected to be encountered while undergoing extreme physical exertion (i.e. catching and subduing struggling prey). The second clue is that Agriotherium has a proportionately short snout to that seen in many other bears. The advantages of having a short snout are simple, it means that whatever is being bitten, is closer to the point of jaw articulation (fulcrum) so that greater force can be brought to bear (no pun intended) against it.
These are all features that are common to Arctodus which also has isotopic analysis of its bones revealing that it was eating nearly every type of animal in its ecosystem, something very unusual for a predator, but common for a scavenger. Given the superficial similarity in form between Agriotherium and Arctodus, it’s reasonable to speculate that Agriotherium may have been a specialised scavenger, a theory that is becoming increasingly put forward for Arctodus. Again, the concept is very simple, by being bigger than any other predator on the land, Agriotherium could in effect bully the smaller predators away from their kills. This draws parallels in bear/wolf interaction that is observed in the wild even today, where grizzly bears will watch a pack of wolves bring down a prey animal, just to charge on in and drive them off after they have done all of the work for it. This fits with the surprisingly gracile skeleton of a large animal like Agriotherium, since if it was letting other predators do the work and the killing for it, why waste precious nutrients and calories upon developing and maintaining a skeleton stronger than it needed to be?
The idea of Agriotherium being what is termed a ‘hyper-carnivore’ is plausible, though it is not certain that Agriotherium only ate meat. Like with bears today, Agriotherium may have also supplemented its diet with fruits and certain plants, particularly tougher ones that required strong jaws. However the scavenger theory does actually fit better with Agriotherium in terms of the age of known fossils. Agriotherium first appears just after halfway through the Miocene before disappearing at the end of the Pliocene. The similar Arctodus however begins to appear in the Pliocene before becoming most numerous during the Pleistocene. It might be that Agriotherium was one of the first specialised scavenger bears but was eventually replaced in the worlds ecosystems by more advanced versions that form separate genera, as well as possibly other bone crunching animals such as hyena.





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Автор: valentint
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