|
Bears of the Pleistocene
|
 (04-05-2018, 12:43 PM)brotherbear Wrote: Spalea, I agree wholeheartedly. I know that it has been accepted now pretty much as fact that Smilodon lived and hunted as a pride. I have read it both ways considering atrox. If the American lion hunted in groups, then they too would have posed a huge threat to the grizzly. If they hunted as individuals like a leopard or a tiger, then probably they would stalk the occasional sub-adult and sometimes a mature she-bear. But, loners or group hunters, the bear would no doubt do his best to avoid them.The short-faced bears in La Bera just left 10 specimens record and even less, it mean they were rare in that period, but the La Brea can't stand for the whole, perhaps in other areas like Texas, short-faced bears were more. 
https://www.floridamuseum.ufl.edu/florid...loridanus/
 *This image is copyright of its original author UF/TRO 96, a jaw belonging to this speciesTremarctos floridanus Quick Facts Common Name: Florida spectacled bear Much more common as a fossil in Florida than the living black bear. Thought to be primarily a herbivore like the living South American spectacled bear. Sometimes called the "Florida cave bear" but they are not closely related to the European cave bear, nor is there fossil evidence of a dependence on caves for denning.
In the Shadow of the Sabertooth by Doug Peacock.
Spanish paleontologists measured a small number of bone pieces and fragments from short-faced bear fossils and inferred that the bear was not short-faced, long-legged, or predacious. A question, which was not asked, is what determines what a bear eats? The answer is behavior, especially aggression, not snout size nor the cut of their omnivore teeth. Animal protein is universally preferred over vegetation. Aggression and dominance no doubt played a huge role, especially around the kill sites of Pleistocene carnivores. Predation among modern bears is opportunistic. The study purported to compare A. simus to the grizzly bear, implying the short-faced bear was a slow moving vegetarian. But grizzlies can outrun racehorses over a short distance and bring down adult elk, caribou, moose and the calves of all these creatures. The short-faced bear evolved in an America without people - grizzlies did not. From my own observations, brown bear routinely displace wolves, cougars and, less commonly, humans from carcasses, presumably because the bear has reason to fear humans. The short-faced bear had no reason to fear H. sapiens because it had never seen one until the late autumn of its species some 13,000 to 30,000 years ago. Other paleontologists studied the teeth, along with some skeletal morphology, of A. simus and concluded the bear's diet largely consisted of coarse foliage by unselective grazing. I ended up wondering how any bear could survive the Beringian winter by unselected grazing of coarse foliage. Sometimes paleontology raises important qualifications in characterizing A. simus as the once-dominant predator in North America. A useful study suggests that because the short-faced bear was incapable of sharp turns or of stopping on a dime ( based on examination of fossil skeletons ), it was therefore not a fierce or pursuing predator. The bear's gracile bone structure argued against wrestling with a mammoth or giant sloth. Having had the opportunity to handle a museum specimen myself, I couldn't agree more that this big-hipped, broad-nosed bear with huge crushing jaws was a superbly equipped scavenger. On a continent crawling with giant predators and prey, carcasses would have been commonplace. The short-faced bear would certainly be a main contender for any kill by any animal within its olfactory range. The large hipbones hint at an animal that could, like a grizzly, stand and scent carrion from several miles away. Modern grizzly bears have been recorded scenting carrion at a distance of nine miles. Standing on its hind legs to reach 15 feet tall, with its wide nostrils flaring, the short-faced bear might have been capable of smelling a carcass at a much greater distance.
In the Shadow of the Sabertooth by Doug Peacock.
Short-faced bears belong to the tremarctine, or "running bears," group of New World bears. Having spent much of a lifetime living close to wild grizzly bears, I don't buy into a demystified edition of A. simus as a peaceful grazing omnivore. With big bruins, behavior is what defines what a bear wants to eat and how he gets it. Grizzlies are true omnivores and prodigious diggers with long claws. Adults can't climb trees. Brown bears hibernate; they dig dens on high mountain slopes. With its great body mass, the short-faced bear couldn't make it up a tree and likely didn't dig much either. Many paleontologists doubt A. simus hibernated. If they could find sufficient protein during the winter by scavenging or predation, they didn't have to. Smaller specimens of the short-faced bear have been found in caves in the contiguous states. These caves are probably not normal lairs but rather, in a species with pronounced sexual dimorphism ( male bears are larger than females ), the winter homes of pregnant females or mothers with young. In solving the argument about what the big bears ate, a key observation is that the grizzly survived the Late Pleistocene and the gigantic short-faced bear did not. The obvious reason, I think, is that the brown bear is a true omnivore, more flexible and adaptable than the meat-eating A. simus. Once the great megafauna declined, the serving portions for scavengers and predators certainly shrunk. If the short-faced bear had been a successful non-selective grazer and browser of shrubs for fruit, it might still be around. Bears can't live by non-selective grazing. If the short-faced bear's broad muzzle, as argued by some of the paleontologists, precluded selecting green grass and sedges from more cellulose-laden forage, then A. simus would have had trouble plucking berries from the bushes they grew on. That makes for a lousy vegetarian. Also, A. simusdidn't den, as far as we know, and would have had trouble finding den sites with caves rare and their claws poorly designed to dig dens. The big bears died off because they couldn't live off plant life when their real food, the great megafauna, dwindled down toward extinction 13,000 years ago. In the Far North, the short-faced bear diet, confirmed by isotope studies ( the nitrogen-15 signature is that of a carnivore ) on fossils, is meat by predation or scavenging. Any sizable carcass in bear country means competition by violent defense and fierce aggression.
In the Shadow of the Sabertooth by Doug Peacock.
At the slow dawn of human consciousness, fearsome beasts prowled the shadows of our primordial fires. They stalked us as dinner on the grasslands, lingered near the mouths of our Pleistocene caves and traveled with us across Beringia into the New World. They were our monsters and our mentors. They became an embryonic chunk of our early religion and we appeased the beasts by painting their images on the innermost walls of the first human art galleries. They were lions, crocodiles and tigers. But mostly they were bears. Of all animals that challenged Homo sapiens, bears are the most humanlike. The rear-paw track looks like our own; they stand upright, have dexrerous forepaws and binocular vision. Grizzlies snore in their sleep and mothers cuff their kids when they mess up. A skinned bear carries an eerie resemblance to a human corpse. Bears are called "same-sized predators." Because bears and men shared a similar omnivore diet, they lived in the same places. Both Neanderthals and Homo sapiens occupied the European rock shelters of cave bears, as well as brown bear, and sometimes the bones of men and bears were intentionally buried together, mingled in the same graves. Everywhere in the Northern Hemishere where early humans traveled they found the tracks of brown bears ( Ursus arctos ). Pleistocene people followed these tracks up into northeastern Siberia and, when the human first crossed over into North America, they walked in the paw prints of bears. The last two large omnivores to venture over from Asia to America were brown bear and human beings. The bear got here first, maybe around 60,000 years ago. People showed up later, probably sometime between 30,000 and 15,000 years ago.
In the Shadow of the Sabertooth by Doug Peacock.
The abundance of gigantic Pleistocene predators means a lot of killing was going on. There must have been intense competition and interaction around the carcasses of big herbivores. Short-faced bears would have challenged lions and sabertooth cats, with dire and Beringian wolves close behind, shadowed by flocks of ravens, magpies, mobs of buzzards and condors. Grizzlies were around too. With humans in Pleistocene America, what was the pecking order? Even if people managed to kill a mammoth or sloth, those other scavenging animals would be close on the scene, especially short-faced bears. And the other bears might be in chase, though not as aggressively as the short-faced variety. Brown bears, over millennia, learned to defer to humans even before European firearms arrived, as told in the ethnologies of Western tribes. Early people hunted in groups, growling or roaring when advantageous; grizzlies have never been known to attack a group of four or more people. The Eurasian brown bear and the American grizzly may look alike but their aggression levels are sufficiently dissimilar to earn the grizzly the subspecies name, Ursus arctos horribilis. When the brown bear crossed over the Bering Strait some 70,000 years ago to the American side, the theory goes, mothers had to protect their cubs from American lions, short-faced bears, wolves and other Alaskan predators on the open tundra. The best defense was a good offense. Grizzlies charged and, when necessary, attacked threats to their young. Corridor routes were closed off roughly 22,000 years ago ( there's a spectrum of opinions here ). At any rate, that seems to be the range of possible pre-Max-dates - 30,000 to 23,000 years ago - for people to have made it southward to mid-latitude North America. Going south was definitely possible. We know it was possible because the grizzly did it. In 2002, a cranial fragment of a brown bear was located in a museum collection of fossils from fluvial gravels near Edmonton, Alberta. This well-preserved bone was subsequently dated, based on two "accelerator radiocarbon dates on collagen," at 26,000 years old ( this is the average of two radiocarbon dates; a recalibrated date would be several thousand years older. The salient point is that it is decidedly before the LGM. Grizzlies came down from Beringia before the two great ice sheets collided, the pre-Max-route. ( We don't know how much earlier. The first grizzly crossed over from Northeast Asia 70,000 to 50,000 years ago. So grizzlies roamed Alberta by 26,000 years ago. Evidence of a grizzly in Alberta 26,000 years ago strongly suggests that a route that humans - if they were in Beringia that long ago - could have used was open for several thousand years and that the habitat along that particular migratory corridor was rich and fully revegetated after prior glaciations. 
The last migration wave of the grizzlies came from 13,000 years ago.
I think the inland grizzlies might all derive from this population as they really bear a lot of resemblance with the brown bears in Northeast Asia.
In the Shadow of the Sabertooth by Doug Peacock.
Understandably, the scientists are guarded on the usefulness of these comparisons. Having tracked, lived with and studied these formidable creatures for more than four decades, however, I firmly believe its a big mistake to dismiss these parallel omnivore worlds. The fundamental fact, which cannot be overstated is biotic habitats that sustain brown bears can also support humans. The only imaginable exception might be an open habitat where humans were vulnerable to short-faced bears and other giant predators but in which grizzlies could have coexisted with the megafauna. Where people and grizzlies both occupied the landscape, how did they get along? There is no early record. Brown bear live in Siberia but the grizzly is more aggressive than his Asian cousin, perhaps suggesting that the Siberian side of Beringia was a less formidable place to live than Alaska.
In the Shadow of the Sabertooth by Doug Peacock.
The reason grizzly remains are seldom found is probably because many of them die natural deaths in their dens. Brown bear are healthy mammals who heal well and rarely succumb to disease. They may live beyond 30 years. Human-caused mortality accounts for most modern bear deaths. Uncommonly, grizzlies are known to use caves to sleep out the winter, but suitable caves are rare and only locally available, usually in limestone topography. Before the short-faced bear succumbed to extinction 13,000 years ago, some of those caves were no doubt already occupied. So the brown bear digs dens. On rare occasion, brown bears have stayed out of the den all winter by appropriating the deer kills of cougars or elk kills of wolves - much like the short-faced bear must have scavenged his way through the Beringian darkness. But the grizzly is not an effective predator. This carnivore cannot subdue enough large animals to keep itself alive in winter. My suspicion is that most grizzly deaths in the wild take place during hibernation, a natural burial in the remote country where brown bears normally dig their dens. Back when both grizzlies and short-faced bears roamed the country, brown bears were not at the top of the food pyramid. The smaller grizzlies would be at a disadvantage trying to compete at a mammoth carcass and could not survive without denning. In coldest Beribgia, this competitive drawback could suffice to drive grizzlies south.
In the Shadow of the Sabertooth by Doug Peacock.
Short-faced bears are carnivores while grizzlies and humans are omnivores. It makes sense to consider A.simus more scavenger than a predator. The larger short-faced bear could have out-competed the grizzly when it came to finding and feeding on carrion. Brown bear need rodents and green plant material from grasses and sedges, roots, tubers, and berries. As winter approaches and these foods become unavailable, U.arctos must dig a den and hibernate. If A.simus could find meat from carcasses all winter long, the big bear didn't need to hibernate.
In the Shadow of the Sabertooth by Doug Peacock.
Grizzlies colonize new habitats slowly. A useful way to think about grizzly society is to see it as an "Amazon" culture. The last grizzlies to survive in a fading bear ecosystem seem to be older females, mothers with daughters. Of course, there has to be a male somewhere. Similarly, female grizzlies dominate biological expansion into new territories. Grizzly bears expand their range into new habitat one female home range at a time. Sows with cubs have small ranges compared to males: twenty to thirty square miles while a boar might range over a hundred square miles or more. The quality of the habitat can shrink or inflate these numbers, less home range necessary along a productive salmon stream as compared to grizzlies on the tundra requiring greater foraging ranges. Typically a daughter sets up her own range adjacent to her mother's. A rough measure of brown bear colonization of suitable habitat unoccupied by grizzlies would be in the range of 20 to 40 miles every five years or so. Brown bears were in Beringia by about 60,000 years ago and around 30,000 years ago they came down an ice-free route to the lower states, probably via an ice-free region as opposed to a corridor between ice sheets. That means that a pre-LGM route was also available to humans for millennia. It was probably open for many thousands of years before the glaciers advancing slammed the route shut around 20,000 or 22,000 years ago. It was an easy route with all kinds of plants and animals.
Note: the book that I am reading ( In the Shadow of the Sabertooth ) is not a book about bears. It is about the advancement of people into "The New World" from Beringia into America during the last Ice Age. The grizzly played a part in this advancement as he was always there a step ahead of humanity. The ancestors of the American Indian walked in the footprints of grizzlies as they entered into North America.
Has anyone any information on Melursus theobaldi ( the brown bear ancestor of the sloth bear ) or on the Chinese original brown bear?
Post by brobear on 5 minutes ago
http://www.nationalgeographic.com/scienc...xtinction/ Extinct Cave Bear DNA Found in Living Bears The discovery is the first of its kind outside the human lineage. After roaming Europe and Asia for more than a hundred thousand years, cave bears died out some 24,000 years ago, after a millennia-long death spiral possibly spurred by hunting, natural climate change, and competition with humans for habitat. No cave bear has awoken from this final hibernation, but the animals' DNA lives on: A new study confirms that about 0.9 to 2.4 percent of living brown bears' DNA traces back to the extinct species. The finding, published in Nature Ecology and Evolution on Monday, marks just the second time that researchers have found an extinct ice-age creature's genes within in a living relative. Humans are the first known example: Between 1.5 and four percent of the non-African human genome comes from Neanderthals, the product of interbreeding between our species and our ancient kin. “By any standard definition, [cave bears] are extinct, but it doesn’t mean that their gene pool is erased, because they continue to live on in the genomes of these living animals,” says Axel Barlow, a postdoctoral researcher at the University of Potsdam and one of the study's lead authors. The study also reinforces that some species regularly interbreed. The DNA of yak and Tibetan cattle, for instance, show signs of interbreeding, as do pig species whose common ancestors lived millions of years ago. In a handful of cases, brown bears and polar bears have bred. And just last week, researchers unveiled the daughter of a Neanderthal woman and a Denisovan man—an example of what may have been widespread hybridization among ancient hominins. “The old-fashioned idea of a species [is that] it's reproductively isolated from other species,” says Rasmus Nielsen, a geneticist at the University of California, Berkeley, who wasn't involved with the study. “This paper is a part of a series of papers that have been saying that worldview really is wrong.” Bearly Breeding? To determine why cave bears died out, Barlow and his research team sought to study how the animals' populations grew and shrank, which they could infer from cave bear DNA extracted from the ear bones of four animals that lived more than 35,000 years ago. First, the researchers compared the overall genomes of cave bears with polar bears and brown bears. Sure enough, the two living species were more related to each other than to cave bears. But the picture got more complex once researchers started counting up the bears' variants of individual genes. Since animal genomes are so large, there's ample room for random variation in certain genes. By chance alone, the same genes in distantly related animals can look similar, and the same genes of closely related animals can look different. In the absence of interbreeding, these quirks pile up in about equal amounts, much like flipping a coin—which isn't what researchers saw among the bears. “If we get an overabundance of genome positions where cave bears and brown bears are showing more similarity to each other than to polar bears, then something else must have happened,” says Barlow. “And that something is hybridization between the two species.” Not only did researchers see signs of interbreeding, but they also confirmed that hybrid bears could breed with either species. When Barlow and his colleague James Cahill combed through the species' genomes chunk by chunk, they found that brown bears and cave bears each had snippets of the other's DNA. “In my view, the concept of brown bears and cave bears interbreeding is not surprising, and it actually makes sense. Overall, they are very similar in appearance, and did overlap in time and space,” East Tennessee State University paleontologist Blaine Schubert says in an email. “However, this possibility was only speculation until the current study.” The cave bears' genetic afterlife resembles Neanderthals' still-present influence on the human genome. But researchers emphasize that there are some major differences, as well. For one, modern humans and Neanderthals are closer relatives than brown bears and cave bears. It's also much easier to study humans and their closest extinct relatives, given the massive amount of sequenced human DNA. Limited data makes it hard to test whether brown bears make use of cave bears' gene variants. In humans, DNA from our archaic cousins affects our immunity, hair structure, and our ability to live in high altitudes, among other traits. But even with limited data, Barlow marvels at what cave bears can still teach scientists, tens of thousands of years after their demise: “I think it’s really nice, because it forces us to think on a philosophical level what we mean by species extinction.” |
| Users browsing this thread: |
| 2 Guest(s) |