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Post by Gorilla king on Jul 2, 2022 14:16:19 GMT -5
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Post by oldindigosilverback on Jul 7, 2022 5:06:54 GMT -5
Not a surprise at all. That is why if a male polar bear fights a smilodon populator, I am sure there will be times the smilodon will end up with broken canines too.
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Post by oldindigosilverback on Jul 9, 2022 9:25:45 GMT -5
Personally I believe the captive polar bear would have won if it did not fall before it manage to give one final attempt due to overheating and outside its natural environment. The tiger was mortally wounded here. Mortal wound = A mortal wound is an injury that will ultimately lead to a person's death. Though I admit the tiger did do well.
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Post by arctozilla on Jul 9, 2022 11:39:23 GMT -5
/\ Already saw the account. It was fictional.
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Post by Gorilla king on Jul 9, 2022 13:37:21 GMT -5
/\ Already saw the account. It was fictional. No, the fictional account you are referring to is from the book "Eyes in the night", the one that has a "15 foot polar bear".
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Post by oldindigosilverback on Jul 9, 2022 17:33:20 GMT -5
/\ A 15 foot polar bear and an orange utan with a knife. There is no way a polar bear can be 15 foot. Even a male polar bear at 12ft is probably skin stretched.
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Post by oldindigosilverback on Jul 31, 2022 4:33:57 GMT -5
Care of Young NursingFemale polar bears have four mammary glands. Mothers nurse their cubs in a sitting position, or lying down on their side or back. During their first few weeks of life, polar bear cubs nurse most of the time and stay close to their mother to keep warm. For the next three or four months the cubs nurse as often as six times a day. The length and number of nursing bouts gradually decreases as the cubs grow older. Mother polar bears nurse their cubs for as long as 30 months. Some cubs stop nursing as young as 18 months of age, but remain with their mothers for survival until they are 30 months old.The average fat content of polar bear milk is 33%, similar to the milkfat of other marine mammals. For comparison, human milk has a 3-5% fat content.. seaworld.org/animals/all-about/polar-bear/care-of-young/#Polar bear cubs stay with their mothers for 30 months meaning that a 2 year old polar bear (24 months old) killed by a barren ground grizzly must have wandered away from its mother. 33% fat in milk on average explains why a polar bear has 30% fat on average.
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Post by oldindigosilverback on Jul 31, 2022 4:37:00 GMT -5
Once mated, females begin depositing fat in preparation for cubbing. Females need to gain at least 200 kg (441 lb.) for a successful pregnancy. seaworld.org/animals/all-about/polar-bear/care-of-young/#A female polar bear needs at least 200kg to be pregnant which explains why some of them have 40% to 50% fat given sows in some areas average 200kgs.
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Post by oldindigosilverback on Aug 6, 2022 7:54:19 GMT -5
How Fast Are Polar Bears? Due to their massive size, polar bears are often thought to be slow. However, the contrary is true. Polar bears are faster than both grizzly and brown bears, reaching speeds up to 35 miles per hour. Comparatively, brown bears reach top speeds up to 30 miles per hour while grizzly bears are slightly slower, at 28 miles per hour. However, polar bears aren’t fast on land only. Classified as marine mammals, polar bears lead a semi-aquatic lifestyle and are excellent swimmers, reaching speeds up to 6 miles per hour in the water. This might seem slow, but it is about the same swimming speed as a walrus. Because of their adaptation to the environment – large, slightly webbed paws and double-layered fur – polar bears can spend a lot of time in the water and swim continuously for over 60 miles. Are Polar Bears The Strongest Bears? Yes, polar bears are the strongest bears. They are not only the largest and fastest of all bears, but they also have the strongest bite force. However, this doesn’t mean they would win in a fight against bears from other species. In fact, in a one-on-one against grizzly bears, the latter would probably win the fight. wildlifeboss.com/how-strong-are-polar-bears/It seems polar bears are also the fastest of all bears.
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Post by oldindigosilverback on Nov 19, 2022 7:00:22 GMT -5
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Post by oldindigosilverback on Nov 30, 2022 21:42:50 GMT -5
An adult male polar bear can weigh up to 600 kg and females are half to two thirds of that. Cubs, depending on their age, are between 25 and 100 kg. The size of a sub-adult polar bear is comparable to that of a large black bear or a medium sized grizzly bear. They are extremely powerful, agile and fast. Their environment is often drifting and broken ice so polar bears are adept at jumping and able to leap surprising distances. parks.canada.ca/lhn-nhs/mb/prince/securite-safety/ours-bear/ours-bear5This is Canadian website so it is no surprise that 600kg is exceptionally large for a polar bear in Churchill. Polar bears might be the best jumpers of all bears.
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Post by oldindigosilverback on Dec 1, 2022 8:21:06 GMT -5
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Post by oldindigosilverback on Feb 5, 2023 4:48:52 GMT -5
www.earthtimes.org/nature/brown-bears-versus-polar-bears/93/The bleak future for polar bears as global warming encourages brown bears to range further north. Something that is not widely realised is that polar bears only evolved as a distinctive species as recently as 200,000 years ago during the Pleistocene. It is believed that today's polar bears are descended from a group of brown bears that became isolated by glaciers in an area near Siberia and underwent a rapid series of evolutionary changes in order to survive and adapt to Arctic life. These involved a change in the colour of their fur, the shape of their body, sharper teeth and large feet with thick, curved, non-retractable claws that are used for grasping prey as well as providing vital traction when running or climbing on ice. Polar Bears are the world's largest land carnivore and the only member of the bear family that is entirely carnivorous. They live on a diet entirely composed of seal flesh and blubber. As a result of this relatively rapid evolution into a semi-aquatic Arctic life with a very specialised diet, the polar bear has developed a cranial morphology that is weaker than that of brown bears and less suited to processing tough omnivorous or herbivorous diets. Polar bears live almost exclusively on the flesh of young ringed or bearded seals. They have 42 teeth and have developed blade-like incisors to shear off pieces of flesh, with strong canine teeth to grasp prey and tear tough hides. Since they swallow most of their food in large chunks rather than chewing it first, strong molars are not necessary and these are much smaller than those of their brown cousins. While their teeth are super-efficient for processing seal flesh and blubber, polar bears' teeth are less suited for processing bones and hard-to-chew diets with lots of vegetation. The polar bear's low, flat skull with its high-sitting eyes is ideal for a semi-aquatic life and it gives them the advantage of being able to thrust their heads into breathing holes or puppy dens. A recent study by the on-line research journal PLoS One (Public Library of Science) says that although the heads and muscle power of polar bears and brown bears are similar, tests reveal that the polar bear's skull is a 'weaker, less work-efficient structure' and does not appear to be well-suited to large amounts of chewing. Although brown bears will eat animals when they are available, they will also eat a large amount of plant material in the summer, which all requires a considerable amount of chewing before it can be swallowed. It is estimated that the world population of polar bears is between 20,000 and 25,000, of which about 60 per cent live in Canada, but the study concludes that as the earth warms and the brown bears continue to range northwards, this is likely to present polar bears with a significant challenge. Where Arctic foxes overlap with red foxes, it is always the red foxes that end up controlling the prime feeding and breeding areas and the fear is that polar bears will share a similar fate.
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Post by oldindigosilverback on Feb 5, 2023 4:49:31 GMT -5
EVOLUTION
Lessons from Polar Bear Studies
This is the first in a series of posts responding to the extended critique of Darwin Devolves by Richard Lenski at his blog, Telliamed Revisited. Professor Lenski is perhaps the most qualified scientist in the world to analyze the arguments of the book. He is the Hannah Distinguished Professor of Microbial Ecology at Michigan State University, a MacArthur (“Genius Award”) Fellow, and a member of the National Academy of Sciences with hundreds of publications, who also has a strong interest in the history and philosophy of science. His own laboratory evolution work is a central focus of the book. I am very grateful to Professor Lenski for taking time to assess Darwin Devolves. His comments will allow interested readers to quickly gauge the relative strength of arguments against the book’s thesis.
Although it was not the topic of his first post, I will begin with Lenski’s discussion of the example with which I open my book — the polar bear genome — because it illustrates some principles that will be useful going forward. For readers who don’t have time to read to the end, here are a couple of take-home lessons:
Experimental evidence strongly supports my conclusion (disputed without good reason by Lenski and others) that highly selected mutations in the polar bear genome work by breaking or blunting pre-existing functions. A “function” of a protein is a lower-level molecular feature or activity, such as being a gear or a tether; it should not be confounded with higher-level phenotypic effects, such as “lowers cholesterol” or “makes the organism happy.” Ignoring the distinction leads to much confusion. Where We Agree At the beginning of Darwin Devolves I discuss work by researchers who compared the genome of the brown bear (Ursus arctos) with that of the polar bear (Ursus maritimus). Those species separated from a common ancestor hundreds of thousands of years ago. By analyzing the DNA sequence data, the researchers were able to determine the genes whose selection most strongly adjusted the polar bear lineage to a frigid environment. One of those genes, called APOB, is involved in fat metabolism. As I wrote:
The scientists who studied the polar bear’s genome detected multiple mutations in APOB. Since few experiments can be done with grumpy polar bears, they analyzed the changes by computer. They determined that the mutations were very likely to be damaging — that is, likely to degrade or destroy the function of the protein that the gene codes for. In fact, about half of the mutations in the 17 most highly selected polar bear genes were predicted to be damaging. What’s more, since many genes had multiple mutations, I noted that about two-thirds to four-fifths of selected genes had suffered at least one damaging mutation. I used this example to set the stage for the main theme of the book, that Darwin’s mechanism works chiefly by degrading pre-existing genetic information, which sometimes helps a species survive.
Echoing blogged arguments by his lesser-known co-authors of the appalling review of my book in Science, Professor Lenski points out (as I repeatedly do in the book) that the computer analysis is a prediction that a particular mutation will or won’t be damaging; it is not an experimental demonstration. In other words, the prediction could be wrong. Further, the program categorizes mutations into just three categories: probably damaging, possibly damaging, and benign. (Benign means simply that, as far as the program can tell, no damage has been done to the protein by that change; it does not mean the change is constructive.) Thus, as he stresses, the program is not set up to detect if in fact some new function had been gained by the protein. He goes on to emphasize that the polar bear is superbly adapted to its high-fat diet — much better in that regard than the brown bear. All of which, I happily agree, is true.
Where We Disagree But then, without benefit of supporting data, Lenski waxes strongly optimistic. He quotes an author of the study and then stresses his own view in bold face:
In a news piece about this research, one of the paper’s authors, Rasmus Nielsen, said: “The APOB variant in polar bears must be to do with the transport and storage of cholesterol … Perhaps it makes the process more efficient.” In other words, these mutations may not have damaged the protein at all, but quite possibly improved one of its activities, namely the clearance of cholesterol from the blood of a species that subsists on an extremely high-fat diet. Lenski is almost certainly wrong about the bolded text. Here’s why. In 1995 researchers knocked out (destroyed) one of the two copies of the APOB gene in a mouse model — the same gene as has been selected in polar bears. Although APOB is itself involved in the larger process of the transport of cholesterol, mice missing one copy of the APOB gene actually had lower plasma cholesterol levels than mice with two copies. (Mice missing both copies died before birth.) What’s more, the researchers noted that “When fed a diet rich in fat and cholesterol, heterozygous mice were protected from diet-induced hypercholesterolemia.”
researchers admitted they did not know how it all came together — how that effect on the complex cholesterol-transport system resulted from breaking the gene. Nonetheless, there is no ambiguity about the mouse results. Simply by lowering the amount/activity of APOB, mice were protected from the effects of a high-fat diet. Deletion of one copy of the gene may have made the process of cholesterol removal more efficient, as Rasmus Nielsen speculated above about the polar bear, but it did so by decreasing the activity of mouse APOB.
Just to be extra clear about the relevance of the mouse results to the interpretation of the polar bear genome, let me state my reasoning explicitly. Given the experimental results with mice, it is most parsimonious to think APOB is broken or blunted in polar bears. For mice, having only half as much APOB activity protects them from a high fat diet. For polar bears, having mutated APOB genes protects them from a high fat diet. If those polar bear mutations decreased the activity of APOB by half or more, then we might expect a similar protective effect as was seen in the mouse. Given that computer analysis also estimated the APOB mutations in the polar bear as likely to be damaging, it is most reasonable to think the activity of the protein has been blunted by the mutations.
Thus there is no good reason to speculate about possible new activities of the coded protein in the polar bear. Rather, the simplest hypothesis is that the mutations in the polar bear lineage that were judged by computer analysis as likely to be damaging did indeed blunt the activity of the APOB protein in that species — that is, made it less effective. That molecular loss gave rise to a happy, higher-level phenotypic result — an increased tolerance of polar bears for their high fat diet.
The Way to Bet The caveats mentioned above by Professor Lenski — about how computer-assignment of a mutation as “damaging” is not a guarantee, and that the protein may have secretly gained some positive new function — are correct. He is also quite right to say that without detailed biochemical and other experiments we cannot know for sure how the change affected the protein and the larger system at the molecular level. Nonetheless, computer methods of analyzing mutations are widely used because they are generally accurate. And they do not suddenly lose their accuracy when I cite their results. So, in the absence of specific information otherwise, that’s the way for a disinterested scientist to bet. There is no positive reason — other than an attempt to fend off criticism of the Darwinian mechanism — to doubt the conclusion.
The APOB gene is exceptional in having such detailed research done on it. Most other genes haven’t been so closely investigated. Nonetheless, in the absence of positive evidence to doubt a prediction for a specific case, the results of the computer analysis should be tentatively accepted for other genes to which it has been applied as well. Skepticism on the matter seems to stem less from the data than it does from reflexive defensiveness. (One of Lenski’s co-reviewers actually talked himself into thinking that “it is entirely possible that none of the 17 most positively selected genes in polar bears are ‘damaged.’” Now there’s a great opportunity for someone to make a few dollars with a friendly wager.)
Lower-Level Functions Versus Higher-Level Purposes I’d like to highlight one final critical point. Let me set it up with a homey analogy. When I was 14 I worked weekends at McDonald’s, and sometimes I’d be assigned to operate the milkshake machine. The machine was broken down each night for cleaning. One of my tasks early in the morning before opening was to reassemble its parts. There were maybe a dozen parts to put together — sprockets, clamps, gaskets, and such. Shakes were very popular back then (mid 1960s) and made many customers happy for a while. Nonetheless, the function of the parts of a shake machine is not “to make people happy.” The function of a sprocket or a clamp isn’t even “to make a milkshake.” Rather, they have lower-level mechanical duties that are subservient to the overarching higher purposes of the systems.
The same is true of APOB. Its function is not “to help polar bears survive,” nor even “to clear cholesterol.” Rather, it has one or more lower level functions that are subservient to those higher purposes. Thus the fact that cholesterol might be cleared more efficiently in polar bears does not at all mean that APOB hasn’t been degraded, any more than breaking the off-switch of a shake machine so that it works continuously throughout lunch hour means some new improved function was added.
In both Darwin Devolves and my Quarterly Review of Biology paper on which it is based, I repeatedly stressed the need to look beneath higher-level, phenotypic changes to associated underlying molecular-level mutations. Did they help by constructing or by degrading what I termed Functional Coded elemenTs (FCTs)? Helpful higher level changes can often be misleading, because they might actually be based on degradative molecular changes. There is every reason to think that’s what occurred in the evolution of the examples I cite in Darwin Devolves, definitely including the magnificent Ursus maritimus. The more effective clearance of its cholesterol allows the polar bear to thrive on a diet of seal blubber, but it is the result of a mutation that breaks or blunts APOB.
evolutionnews.org/2019/03/lessons-from-polar-bear-studies/
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Post by oldindigosilverback on Feb 5, 2023 4:53:24 GMT -5
An Arctic legend, an ancient skull & a strangely shaped polar bear.In the northernmost reaches of Alaska, not far from the city of Barrow, lies an ancient site named Walakpa, which was home to Inuit people between 700 and 800 years ago. There, archaeologists have spent decades digging up the remains of buildings, tools, and a variety of local animals, including one very intriguing polar bear skull. Any polar bear skull is a sight to behold, but this one, discovered back in 2014, caught the eye of researchers. At about 40 cm (16 in) long, it's larger than most of the ancient bear skulls found in this region, and its slender shape brings to mind a legend passed down through generations of local hunters: the tale of the weasel bear. The ancient residents of Walakpa belonged to the Iñupiat Birnirk culture, which appeared around 600CE, constructing homes across the Arctic. These resourceful people had few plants to depend upon, so nearly everything they needed – food, clothing, tools, building materials and more – they got from the body parts of local mammals, particularly marine creatures like seals and whales. "Hunters have a thorough knowledge of these animals and their behaviour, which is passed down from generation to generation," says Anne Jensen of the Ukpeagvik Inupiat Corporation Science Division, part of the Walakpa archaeological team. Lurking in local lore are descriptions of an unusual type of polar bear: large, skinny and long-bodied. The local name for these creatures is tiriarnaq, meaning "weasel bear", in reference to their narrow frame. The accounts are striking enough that some have even wondered if these animals might represent a separate species or subspecies. So, could the newly unearthed bear skull represent a weasel bear? The researchers aren't sure, but they do have plans to find out. According to Jensen, similar-looking skulls have been spotted at the University of Alaska Museum of the North by her colleague Raphaela Stimmelmayr from the North Slope Borough Department of Wildlife Management. The team plans to extract DNA from the Walakpa skull, which is well-preserved enough to retain soft tissues, and compare this to modern polar bears. "If it does look different, the next step would be to get permission to sample the similar skulls in Museum of the North, both for dating and for DNA," Jensen says. If these "weasel bears" are indeed a different type of bear, their genetic data should show it. The idea that the skull might represent a species unknown to science is definitely intriguing, but polar bear researcher Andrew Derocher of the University of Alberta suspects this isn't the case. "[T]here's nothing unusual about this bear when it comes to length," he says. The skull might be large compared to others dug up in this area, but Derocher points out that 40cm (16in) is about average for the skull length of living polar bears. And when it comes to legends, Derocher has heard not just of the long, skinny tiriarnaq, but also of short, stocky animals sometimes called "badger bears". Polar bear body shape, he argues, can vary quite a bit: "There are long and thin and short and stocky bears. If you focus on the ends of the spectrum, you could easily come up with the weasel and badger bears." In his view, the Walakpa skull may simply have belonged to a lanky, but otherwise unexceptional, individual. Time may tell us more about these animals, but time is not on the archaeologists' side. The new bear skull was found after intense erosion exposed new material at Walakpa, and this kind of landscape change is becoming more and more common all along Arctic coastlines. "Most of the sites along the Beaufort Sea coast of Alaska already have been severely damaged, if not obliterated," Jensen says. The cause is familiar: a warming climate. In the cold winter months, coastal waters in Alaska are covered in sea ice, which blocks waves from reaching the shore. But as these waters warm, the ice persists for fewer months of the year, allowing more waves to chew into the land. What's more, the permafrost that holds the soil together thaws more in warmer years, leaving the ground more prone to erosion. "In the past, the usual procedure was to only excavate parts of a site," Jensen says. This meant portions of a site were left undisturbed for future decades, when improved technologies and methods might allow for more thorough excavation. "Obviously, with sites disappearing as rapidly as they are, that is no longer a good strategy," she adds. The disappearing sea ice is bad news for bears too – weasel or not. "The main threat to polar bears is sea ice loss," Derocher says. "The sea ice is the primary habitat of polar bears and it's where they make their living." While researchers continue to work to understand these animals, past and present, the world that supports them all is steadily melting away. www.earthtouchnews.com/discoveries/discoveries/an-arctic-legend-an-ancient-skull-a-strangely-shaped-polar-bear/__
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Post by oldindigosilverback on Feb 5, 2023 4:53:59 GMT -5
esajournals.onlinelibrary.wiley.com/doi/full/10.1890/06-0624.1 Arctic Marine Mammals Polar bear (Ursus maritimus) Polar bears are similar to brown bears (Ursus arctos) in size and mass but are generally longer and slenderer. They have a downturned rather than dished face. Adult males weigh 350–650 kg, and adult females weigh approximately 150–300 kg. They are covered with whitish fur except for the nose and footpads. Canine teeth are well developed, and cheek teeth are more trenchant than those of other bears, reflecting evolution from an omnivorous to carnivorous diet (Kurtén 1964). Arctic adaptations include: white coats that help camouflage them and aid in stalking seals; dense fur and thick body fat, providing insulation from cold air and water (further, body fat helps buoy up the animal); a streamlined teardrop body shape and large, oar‐like paws that enable them to swim well and the paws act like snowshoes on thin, newly formed ice; short furry ears and large body size that help to conserve heat; an extremely well‐developed sense of smell that aids in finding food and bringing together the sexes over vast icy expanse during the breeding season; the ability to make dens in coastal snowbanks, providing protection for the mother and her (usually) twin cubs during the coldest period of the year; hunting techniques such as sniffing out and breaking into seal dens and waiting by seal breathing holes. Polar bear fossils are confined to the Pleistocene (Kurtén 1964). Both fossil and molecular data indicate that polar bears stemmed from brown bears about the Middle Pleistocene (perhaps 400000–300000 years ago) (Kurtén 1964, Talbot and Shields 1996). Middle Pleistocene climatic cooling probably influenced the evolution of the ancestor of the polar bear (Kahlke 1999). Yu et al. (2004), by combining nuclear and mitochondrial DNA findings, have gained new insight into the evolutionary history of the bears (Ursidae). Their results corroborate other morphologic and genetic evidence indicating that brown and polar bears are most closely related and suggest that polar bears split from brown bears between 1 and 1.5 million years ago (Ma). The divergence of polar and brown bears probably occurred somewhere along the coasts of Siberia or Alaska, but pre‐Holocene fossils are scarce. Heaton et al. (1996) note that differences in mitochondrial DNA sequences suggest that living brown bears of the Alexander Archipelago, southeastern Alaska, comprise a distinct clade and are most closely related to polar bears. Could that be a clue as to their place of origin? I speculate that the drift from an Arctic coastal brown bear with a grayish coat to a polar bear began with the former specializing in scavenging beached marine mammal carcasses. Gradually, the bears might have ranged farther out onto the sea ice (fast ice) where they could actively prey on young seals in their dens and then on adult ringed seals at their breathing holes. In this respect, it is worth noting that grizzly bears (Ursus arctos) are now regular visitors to the Canadian Arctic Islands. On the sea ice of Viscount Melville Sound, remains of seals as well as female polar bears and their cubs have been attributed to kills by grizzly bears. Perhaps one of these bears denned on Melville Island during the winter of 2003–2004 (Doupé et al. 2007). Breakthroughs would come with genetic selection for white coats (camouflage) to aid their hunting (Sterling 1989:26), as well as adaptation to denning in dense snow near sea coasts rather than in earth farther inland, and physical adaptation for more trenchant teeth to support the more carnivorous diet, as well as large, oar‐like feet to enhance their swimming ability. The oldest known polar bear fossils are a relatively large right ulna from presumably Early Weichselian (approximately 70000 BP[?]) gravels of the Thames at Kew Bridge, London, and a left lower jaw from >80000 BP deposits on Svalbard (O. Ingólfsson, personal communication).2 The Kew Bridge find induced Kurtén (1964) to create a new gigantic Late Pleistocene subspecies Ursus maritimus tyrannus. Stuart (1982) calculated that the Kew locality was at least 140 km from the Devensian (last glaciation) coastline, based on the assumption that sea level was at its lowest then. Further, the presence of a marine mammal fauna, including ringed and bearded seals, suggests that polar bears too were present in the southern North Sea during the Late Pleistocene (at several colder intervals during the Weichselian) (Post 2005). Also, it is possible that outlines of bears in the Paleolithic cave of Ekain, northern Spain, may indicate that polar bears drifted south from the edge of pack ice off southern England (see map on the cover of Preece [1995]) to the northern coast of Spain during heavy ice years toward the close of the Pleistocene. I interpret the bears to be twin subadult polar bears from their teardrop body shapes (Bahn and Vertut 1988: Fig. 90). These images were probably made during the Magdalenian (approximately 17000–12000 years ago). The latest Weichselian to Early Holocene colonization of the western coastal regions of Norway, Sweden, and Denmark (northern Jutland) are well documented. A large lower jaw of an adult male polar bear dated to 11100 ± 160 BP from near Asdal (Jutland) occurs in the Allerød (Aaris‐Sørensen and Petersen 1984). Eight finds (from Scania [two], Halland [one], and Bohuslän [five]) are known from Sweden (Kurtén 1964, Liljegren 1975). The more southerly specimens from Scania are dated at 12710 BP and 12490 BP (Håkansson 1974, 1976). Two of the finds from Bohuslän have been dated to 10620 BP and 10430 BP (Håkansson 1976). A nearly complete skeleton of a large male nearly 30 years old from Judaberg (Finnøy, Norway) has been dated at 10660 BP. It shows that polar bears were present in the Younger Dryas High Arctic marine environment in southwestern Norway (Blystad et al. 1983). Otto Salvigsen (personal communication) has dated (about 8200 BP) polar bear bones from a marine section on Svalbard. Fossil finds from Siberia are rare and not well dated. Vereshchagin (1969) records a right ulna from near the mouth of Mordy‐Yahk River on the western coast of the Yamal Peninsula. Fossil remains of walrus and white whale were found there too. Also identified as belonging to the polar bear are: a right first molar stained black (Pleistocene?) found in 1961 on the shore of the Pechora River, as well as abundant remains from the Mesolithic site on Zhokhov Island (approximately 9000–8000 BP) (G. F. Baryshnikov, personal communication). The early inhabitants of Zhokhov Island in the Siberian Arctic evidently relied heavily upon polar bears for subsistence. Many of the bones from the site exhibit cut marks. Skull measurements suggest that female bears with cubs were killed in winter by hunters seeking their dens (Pitulko and Kasparov 1996, Pitulko 2003). In northern North America, the oldest radiocarbon‐dated specimens from Vandfeldsnaes, Greenland, and Cape Richard Collinson, Prince of Wales Island, Canada, are only about 2000 years old (Harington 2003a:383). Fulton and Strobeck (2006: Fig. 3a) provide a succinct view of relationships among bears. Note particularly the closeness and relatively recent evolution of polar and brown bears (Fig. 2). Relationships among the bears according to a maximum‐likelihood cladogram recovered from all genes (Fulton and Strobeck 2006: Fig. 3a). Note the relatively recent divergence of polar and brown bears. Values above the branches are maximum parsimony (MP) bootstrap/Bayesian posterior probability (BPP) values. The nodes that do not have support values were polytomous in both topologies. Modern and fossil distributions of polar bears are given in Vereshchagin (1969:46, Fig. 6) and Laidre et al. (2008).
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Post by oldindigosilverback on Feb 5, 2023 4:55:51 GMT -5
www.theguardian.com/science/2011/jul/07/polar-bear-ancestors-irelandModern polar bears are partly descended from extinct brown bears that lived in Ireland during the last ice age, scientists have discovered. It's a long way from the Arctic to Tipperary, but scientists have discovered polar bears can trace their family tree to Ireland. Genetic evidence shows they are descended from Irish brown bears that lived during the last ice age. Modern polar bears share a distinct DNA sequence, passed down the female line, with their now extinct brown ancestors. However, the same DNA fingerprint is absent from other species of brown bear alive today. It is thought the link arose from interbreeding between prehistoric polar bears and female brown bears when their paths crossed as the Irish climate cooled. Scientists made the discovery after analysing DNA in mitochondria – energy-producing structures within cells – that are only passed from a mother to her offspring.
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Post by oldindigosilverback on Feb 5, 2023 4:57:36 GMT -5
www.theguardian.com/science/2011/jul/07/polar-bear-ancestors-irelandModern polar bears are partly descended from extinct brown bears that lived in Ireland during the last ice age, scientists have discovered. It's a long way from the Arctic to Tipperary, but scientists have discovered polar bears can trace their family tree to Ireland. Genetic evidence shows they are descended from Irish brown bears that lived during the last ice age. Modern polar bears share a distinct DNA sequence, passed down the female line, with their now extinct brown ancestors. However, the same DNA fingerprint is absent from other species of brown bear alive today. It is thought the link arose from interbreeding between prehistoric polar bears and female brown bears when their paths crossed as the Irish climate cooled. Scientists made the discovery after analysing DNA in mitochondria – energy-producing structures within cells – that are only passed from a mother to her offspring. Full-grown male tigers neither hunt nor fight full-grown male brown bears. brobear Administrator ***** Administrator brobear Avatar single Posts: 20,893Male Member is Online Reply #37 posted Oct 10, 2021 at 6:27pm tom likes thisQuotelikePost OptionsPost by brobear on Oct 10, 2021 at 6:27pm www.nature.com/articles/news.2010.99Ancient polar-bear fossil yields genome. Oldest mammalian DNA sequence reveals link to brown bears. DNA from a 110,000–130,000-year-old polar-bear fossil has been successfully sequenced. The genome, from a jawbone found in Svalbard, Norway, in 2004, indicates when polar bears (Ursus maritimus) diverged from their nearest common relative, the brown bear (Ursus arctos). Because polar bears live on ice and their remains are unlikely to be buried in sediment and preserved, polar-bear fossils are very rare. So even the discovery of a jawbone and canine tooth — the entirety of the Svalbard find — is impressive. But far more important, is that when molecular biologist Charlotte Lindqvist, then at the University of Oslo's Natural History Museum and now at the University at Buffalo in New York, drilled into the jaw, she was able to collect intact mitochondrial DNA. Mitochondria — organelles found in animal cells — have their own DNA and can replicate. And because there are many mitochondria per cell, mitochondrial DNA is easier to find in fossils than the nuclear DNA. Lindqvist wondered whether this mitochondrial DNA could illuminate the evolutionary history of how and when polar bears diverged from brown bears. To find out, she worked with Stephan Schuster, a molecular biologist at Pennsylvania State University in University Park, and a team of colleagues to sequence the genetic material she had collected. Bring the bear necessities to life The team found that the mitochondrial DNA strands were fragmented and partly degraded. The strands of mitochondrial DNA were broken up and some of the base pairs, such as adenine and cytosine, were altered by decay. Even so, because the DNA was preserved in a region so dry and cold, it was less damaged than is usual for such ancient DNA. The team used high-throughput sequencing to isolate short fragments of DNA. Because the DNA from many mitochondria was mixed in the fossil, the team got many reads for exactly the same sections. This meant that the researchers could detect and compensate for degradation events. It is the oldest mammalian mitochondrial genome yet sequenced — about twice the age of the oldest mammoth genome, which dates to around 65,000 years old. "Many researchers would have thought it impossible to retrieve DNA from a bone specimen as old as this polar bear," says Eske Willerslev, an evolutionary biologist at the University of Copenhagen. "The result is a true eye opener — it gives hope to future projects trying to genome sequence truly old bone specimens." Wherever I wander, wherever I roam The researchers then compared the fossil DNA sequence with the DNA sequences of modern brown and polar bears. They found that the fossil DNA shared many of the gene sequences found in brown bears and lacked many that polar bears have. This raised the question of whether the ancient bear lived like a polar or brown bear. A comparative analysis of stable isotopes in the fossil's canine tooth with isotopes collected from the teeth of modern polar and brown bears showed that the fossil bear's diet was similar to that of modern polar bears — mostly marine mammals such as seals and small whales. There was no evidence that the bear had fed on the mix of freshwater fish, land mammals and plants that make up the brown-bear diet. Palaeontologists also excavated fossils of arctic marine animals in the sediment where the bear fossil was found. These indicated that the animal had clearly been living in an arctic marine environment as modern polar bears do and not the inland locations that brown bears prefer. "Morphologically and behaviourally it was a polar bear, but genetically, it was almost a brown bear. This fossil is amazing since it looks to be pretty much at the exact point when polar bears split from brown bears," says Lindqvist. The team reports in Proceedings of the National Academy of Sciences that the fossil indicates polar bears broke away from the brown bear lineage not more than 150,000 years ago and evolved from being terrestrial predators into their modern niche of ice-dwelling hunters in just 10,000–30,000 years1. "This is one of the most exciting things to come up in polar research in the past 20 years," says Ian Stirling, an ecologist at the University of Alberta in Edmonton, Canada. There have been questions about whether polar bears diverged from brown bears a million years ago or more recently, he says, and "it is great to see such strong data clarifying that the divergence is recent". Yet their history of quick adaptation will do little to help the bears survive global warming. "Extremely fast from an evolutionary perspective is tens of thousands of years, not decades. If warming continues at the high rate that we are seeing today and the bears' ice habitat is destroyed, the species is going to be in serious trouble," says Lindqvist.
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Post by Gorilla king on Feb 27, 2023 20:04:32 GMT -5
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Post by arctozilla on Feb 28, 2023 2:56:53 GMT -5
Poor mother bear
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