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Bear Evolution
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The Cave Bear Story... Thrown into such ( for a bear ) completely novel circumstances, the polar bear probably evolved quite rapidly, under strong pressure by natural selection to adapt it to its new mode of life. This evolution is evidently still going on, for fossil finds during the last 10,000 years show that there have been distinct changes in some of its characters, although in an evolutionary perspective this is a very short span of time.
In the modern world there are three other species of bear, which do not belong to the Ursus line. The sun bear, or Malay bear, has already been mentioned. This small species, no larger than Ursus minimus of the Pliocene, is yet quite distinct in its anatomy, and so it is regarded as a genus of its own, Helarctos. Its history is only known from the Ice Age when it already looked very much like the living form.
The Cave Bear Story... The second species is the sloth bear of India, "Baloo" of Rudyard Kipling's Jungle Book. It also belongs to a genus of its own, Melursus. A medium-sized bear, the sloth bear looks anatomically somewhat like an overgrown Ursavis, but again we have no reliable information on its history before the Ice Age.
http://www.eartharchives.org/articles/ki...tter-bear/
One of the most unusual marine mammals of all time was Kolponomos, the “otter-bear”. Details of this enigmatic animal have remained quite a mystery for many years since its discovery. Now, scientists have finally figured out the secret behind the otter-bear’s deadly bite, and just how it managed to survive. Fossils of the aberrant early bear Kolponomos first surfaced in parts of the Olympic Peninsula and all along the Pacific coast of North America. The bones were named by Ruben A. Stirton in 1960, and he thought it to be some kind of raccoon before realizing that it was something else entirely. More remains started to emerge subsequently from Oregon, Washington and other areas. Soon, a better picture of the creature came to light, an animal that seemed to defy classification on all counts. There is no complete skeleton so all that is known about it must be gleaned from parts of skulls, jaws, neck and foot bones. It was a bear with the habits of a sea otter, a coastal creature that dealt with hard-shelled invertebrate prey. Recent studies from the American Museum of Natural History also show that it bit into and dispatched its prey just like a saber-toothed cat. This new development was brought to light by scientists including Camille Grohe, a National Science Foundation and Frick Postdoctoral Fellow in the American Museum of Natural History's Division of Paleontology. One of Grohe’s collaborators, Z. Jack Tseng, elaborated that the famous saber-tooth Smilodon was probably the least expected analogue to Kolponomos. Grohe, Tseng and their team had included a number of other predators in the study, like sea otters, grey wolves, river otters, brown bears and leopards. Oddly enough though, it seemed to fit. Both the bear and the cat used a similar system of lower jaw-swings to deliver the killing bite. The shear-bite hypothesis is one that has been tested for these cats many times, and involves the lower jaw teeth being anchored in place on a struggling victim before the sabers could come in and close the deal. On their own, the jaws and sabers of Smilodon were relatively weak, so it was an incredibly powerful and muscular neck doing all the action. Just like the cat, Kolponomos would have used its lower jaw to help pry shellfish off rocks, with its neck backing up the jaw to provide more power. Once in the mouth, it would be the task of the molars to crush the shells of whatever was caught. Thus the so-called “otter-bear” combined the killing techniques of both sea otters and Smilodon in one strange package.
http://www.abc.net.au/news/2016-04-20/pr...ng/7338852
Ancient bears evolved to become giants so they could scavenge prey killed by others, a new study suggests. The findings, published in the Royal Society journalBiology Letters, found that short-faced bears weighing over a tonne evolved independently in North and South America. "We think their large size was a particular advantage that let them exploit carcasses from other predatory species," said evolutionary biologist Dr Kieren Mitchell from the University of Adelaide, who was lead author on the new paper. Dr Mitchell said giant bears from the Tremarctinae group were among the largest land-based carnivorous mammals that ever lived. The bears roamed the grasslands and open woodlands of the New World from about 2.5 million years ago to about 12,000 years ago. The animals strode around on their long legs, eating whatever they could find, but the shape of their teeth suggests they were better adapted for eating meat than plants, he said. At the time the giant bears lived there would have been lots of large herbivores, such as bison and mammoth in North America, and horses and giant ground sloths in South America. There would also have been specialised predators like wolves, lions and sabre-tooth cats, but there would have been no specialised scavengers, Dr Mitchell said. "This opened up a bit of a gap that looks like the bears took advantage of separately in North and South America." By turning into giants, the bears could spot vultures circling and quickly get to any newly-killed prey and get a meat meal without the risk and energy of having to do their own hunting. "They could just get anything out of the way that was there originally, and just tuck in," Dr Mitchell said. The giant bears in North America belonged to the genus Arctodus while in the South America it was the genus Arctotherium. Both were members of a group, which today has only one living member — the much smaller and largely vegetarian Andean spectacled bear (Tremarctos ornatus). To shed light on the evolution of the giant bears, Dr Mitchell and colleagues compared the mitochondrial DNA of Arctotherium and Arctodus bears with the DNA of the living spectacled bear. This included DNA extracted from a femur of a giant bear found in a cave in Chile and DNA from the largest species of North American giant bear Arctodus simus. The genetic analysis showed the South American giant bear was more closely related to the modern bear, even though it looked more like the North American giant bear, indicating the two extinct species evolved independently as an adaptation to exploit a similar ecological niche. 
At the time when Arctodus simus had spread in the western part of South America during the late Pleistocene, Arctotherium angustidens was already gone to extinction.
It was a pity that these two titans of the bear family had never met face to face in the history. 
Nice topic, I was searching for it. I heard of beardogs can anyone help me with it.
Polar bear ancestry, nice article. It says polar bear originated from single female brown bear.
http://www.wired.com/2011/07/polar-bears-origins/
http://www.polarbearsinternational.org/a.../evolution
Estimates of when polar bears began to split from brown bears continue to change as geneticists look further into the polar bear genome. Recent studies suggest that polar bears split from a common brown bear ancestor 350,000-6 million years ago. After beginning to branch off from brown bears, the polar bear's ancestors underwent a series of evolutionary changes in order to survive in the Arctic. The bears adapted to a life of hunting seals and surviving extreme cold. One of the most remarkable adaptations was the ability to thrive on a fat-rich diet without apparent heart damage. Interestingly, the research shows that after brown bears and polar bears separated, there were periods when they came into contact again, particularly with polar bear genes flowing into grizzlies. What does this mean in the face of the current arctic warming now taking place?
https://www.sciencealert.com/a-mini-ice-...t-15-years
https://www.livescience.com/51597-maunde...e-age.html A scientist who claims waning solar activity in the next 15 years will trigger what some are calling a mini ice age has revived talk about the effects of man-made versus natural disruptors to Earth's climate. Valentina Zharkova, a professor of mathematics at Northumbria University in the United Kingdom, used a new model of the sun's solar cycle, which is the periodic change in solar radiation, sunspots and other solar activity over a span of 11 years, to predict that "solar activity will fall by 60 percent during the 2030s to conditions last seen during the 'mini ice age' that began in 1645," according to a statement. At the National Astronomy meeting in Llanduno, north Wales last week, Zharkova said that a series of solar phenomena will lead to a "Maunder Minimum," which refers to the seven decades, from 1645 to 1715, when the sun's surface ceased its heat-releasing magnetic storms and coincided with the Little Ice Age, a period of chillier temperatures, from around 1550 to 1850 in Europe, North America and Asia, according to NASA. (06-11-2016, 04:44 PM)brotherbear Wrote: http://www.polarbearsinternational.org/a.../evolution It is possible that the mixture of the non-brown bear gene could have triggered the mutation of the polar bear. Maybe the ancient mixture of the polar bear came from the cave bear. 
Recent news found by Brobear says that the largest cave bear (Ursus ingressus) has now been changed to (Ursus Kanivetz).
As with most prehistoric creatures in pop culture, they are typically shown as being wild, ravenous and savage bruins ubiquitous to a primeval world. Make no mistake - while any bear, especially one that grows to 400+kg, is a formidably well-armed and potentially very dangerous animal to humans, the evidence strongly suggests that cave bears were almost purely herbivorous. Ursus dolinensis, the Gran Dolina cave bear. This is the most basal cave bear species known, with morphological analyses showing a suite of primitive traits, placing this bear very close to the common ancestor with U. arctos. The original remains of this diminutive bear are known from the eponymous site of Grand Dolina in the Atapuerca mountains in Spain, though subsequent remains attributed to this species have also been found in Germany.[5] Dating at these sites puts the Grand Dolina cave bear at an age of about 1 million to 780,000 years ago, the Early Pleistocene. Ursus savini, the steppe cave bear. This species is considered as a sister species to U. deningeri. The steppe cave bear was first described in 1922 from middle Pleistocene deposits in Bacton, England, but fossil evidence has also led to the inclusion of some more recent cave bear taxa (previously thought to be closer allied to U. deningeri) as late subspecies of U. savini.[6] The far-flung locations of these subspecies suggest that the steppe cave bear had an Asian-Siberian origin, and their environmental context, as well that of the type locality, has led to its christened common name. Based on craniodental morphology, the authors of a new 2017 study have argued that it was well adapted to grazing (most other cave bears appear to have preferred boreal forest areas), and environmental data puts the bears in mosaic landscape settings of mixed woodland and steppe - hilly, but not mountainous.[6][7] Two subspecies of this bear are currently recognized: Ursus savini nordostensis, the Beringian cave bear. The most northwestern cave bear know, found in Cherskiy, in the northeastern part of arctic Siberia, along the Kolyma river. The dating for its locality are very imprecise, ranging from between 0.5 and 1.5 million years.[2] The environmental settings in which it was found indicates steppe-tundra, with very few caves. While it inhabited what is technically known as Beringia, there is no evidence that it spread to North America. Based on its remains, it appears to be a relatively small bear, at about the size of a modern black bear. Ursus savini rossicus, the Krasnodar cave bear. Named after the type locality of Krasnodar, just north of the Russian Caucasus, the Krasnodar cave bear was found across the south of Siberia, as well as parts of Eastern Europe, including the Ukraine and as far west as Bulgaria,[6] and was a relatively small (but robust) bear, about the size of a modern black bear. In the past, it has been debated whether the Krasnodar cave bear should be considered its own species, or merely a subspecies of steppe cave bear on the basis of morphmetrics. For a while, aDNA evidence from remains from Kizel cave in the Urals placed the Krasnodar cave bear as a sister group to the Medvezhiya cave bear (see below..),[8] but these Uralian bears are now argued to be dwarf forms of the latter lineage.[6] The Krasnodar cave bear is known to have existed throughout the middle and late Pleistocene, with the most recent remains dating to about 28.9 thousand years ago Ursus deningeri, Deninger’s cave bear (the identity of the Deninger in question evades me). It lived between 1.8 million and 100 000 years ago (though that upper estimate seems questionable), and inhabited much of Europe, Anatolia,[8] and parts of the middle east. It is believed to be a sister lineage to the steppe cave bear and ancestral to the below cave bear species (or at least the U. spelaeus-kanivetz group), and possesses more primitive, less robust features than its more derived descendants,[10] being comparable in size to a modern brown bear. Isotopic testing and support the contention that this species was herbivorous, though some have argued for a more omnivorous diet based on dentition. Ursus kudarensis, the Kudaro cave bear. Formerly considered Ursus deningeri kudarensis, but now considered separate for reasons mentioned above. Still, aDNA suggests it split from the U. spelaeus-kanivetz group between 274,000 and 814,000 years ago.[15] It is named after the Kudaro caves in the Georgian Caucasus, a paleolithic site from which the first remains were found, as well as some Mousterian artifacts. It was a fairly large-bodied cave bear, larger than a modern brown bear and comparable in size to the classical cave bears of Western Europe. Ursus kanivetz, the Medvezhiya cave bear. The largest of the great cave bears, at up to 1.4m tall at the withers and weighing up to around 400–500kg.[27] It inhabited much of Eastern and Central Europe, the Urals, and, later on, parts of Western Europe. Until very recently, this bear bear was referred to as Ursus ingressus, or the Gamssulzen cave bear (indeed, Wikipedia’s recent article on this bear still refers to it by the old name), by Rabeder and Hofreiter (2004),[17] and almost all of the literature available will refer to this bear by this name. But aDNA analyses in 2016 revealed the type specimen to be a congener with cave bears from Medvezhiya cave in the Urals, once named U. kanivetz in 1973 by N. K. Vereshchagin.[18] Thus the older name has superseded the younger one. From the molecular data, we know that the Medvezhiya cave bear was a sister species U. spelaeus, with an estimated split date of 170,000–400,000 years ago. Ursus spelaeus, the western cave bear. Finally, we find our familiar Ursus spelaeus. The great cave bear of western Europe. A sister species to the Medvezhiya cave bear, they inhabited most of Western Europe and the Alpine region, but evidence shows that some small populations were more widespread than that. Even here, three subspecies have been recognized since 2004: Ursus spelaeus ladinicus, the Conturines cave bear. One environment where cave bears weren't expected to be found was that of the high alps, especially during colder periods, since the flora at such high altitudes were thought to be unable to support such a large bear. Nonetheless, in the Alps, the remains of dwarf forms of U. spelaeus between 30-60kya over 2km a.s.l established their presence in the Italian Dolomites, at sites such as, yes, Conturines cave. This has led some scientists to conclude that the Dolomites were at least as warm as, if not warmer than, today.[22] In any case, the Conturines cave bear was a basal lineage within the western cave bears, and is known to have existed in the Italian Dolomites, as well as parts of nearby Slovenia, and aDNA shows that they were also found in southern France, at the Merveilleuse cave, and Belgium, at the Scladina cave.[23] This species was quite a bit smaller and more gracile than the larger, more familiar subspecies we’ll look at, at about the size of a black bear. Ursus spelaeus eremus, the Ramesch cave bear. Another alpine subspecies, found in and around the Alps, in what today comprises parts of Austria, Switzerland, Italy and southern Germany. Intriguingly, aDNA reveals the presence of this species at the Denisova and Strashnaya caves in the Siberian Altai - 7000 km east of their known center of distribution.[15] It is also from this subspecies that scientists first uncovered strong evidence for the distinction of the Western and Medvezhiya cave bears. Between 30,000 and 50,000 years ago, U. k. ingressus is known to have inhabited the Totes Gebirge region of the Austrian alps, occupying Gamssulzen cave. Less than 10km, a mere 2-hour walk apart (human standards, bears can move faster, I do believe), Ramesch cave was situated, and this is where Ramesch cave bears are known to have hibernated. Dating shows a period of overlap between the two bear lineages of about ~15,000 years. Yet we know from aDNA that there was no gene flow between the two caves, which remained both genetically and morphologically distinct.[25] Their separation has been more recently been compounded by isotopic analysis of their bone collagen, reflecting their diets when the two coexisted. By en large, the bears possessed two distinct (herbivorous) diets, with very little overlap. Using oxygen isotopes, scientists were able to determine that they may even have used different water sources as well, indicating that they may not have occupied the same landscape, either separated in space or in time due to climatic shifts.[26] This suggests that they had become reproductively isolated for long enough to undergo a full speciation - making the Ramesch-Gamssulzen divide a classic example of the separate species concept. If the names of the caves sound familiar, it’s because this study is what originally led to the naming of U. (k). ingressus and U. s. eremus, and their (initial) common names. Ursus spelaeus spelaeus, the classical cave bear. This is the species with which we are most familiar with. This subspecies was widespread in western Europe, from the Swabian Jura all the way west into the Iberian Peninsula. The earliest remains were named in 1794, from Zoolithen cave, which were later found to form a distinct genetic lineage withing the species.[29] It was a very large bear, the largest of the three subspecies, at up to 400kg or more,[28] and at around 1.3m tall at the withers, and a tad bit smaller than the Medvezhiya cave bear. These were the bears which were immortalized in the paleolithic art at Chauvet cave, and in the carvings at Geißenklösterle.[33] Interestingly, genetic studies analysing mtDNA of cave bears at cave sites in Spain, reveals strong evidence that cave bears returned to hibernate in the same caves in which they were born, which explains the distinct haplotypes in the Totes Gebirge.[30] The classical cave bear suffered a decline in genetic diversity towards the end of its lifetime. Finally, around, 32,000 years ago, a westward migration of Medvezhiya cave bears moved into the Swabian Jura, possibly due to worsening habitat conditions in eastern Europe. Unlike the case in the Totes Gebirge, they did not coexist, and instead the classical cave bears appear to have been outcompeted and replaced by their larger relatives.[31] However, more recent evidence suggests that these bears clung on for around 3,000 years later, as remains of this species dated to 28,730-28,500 years BP from southeastern France reveal. These bears still retained a similar diet to their earlier ancestors, suggesting they may not have had very flexible diets. Interestingly, these recent remains show evidence of human butchery. http://domainofthebears.proboards.com/post/20503/thread |
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