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Bears of the Pleistocene

United States brotherbear Offline
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Spalea; when I was a kid, I was dinosaur crazy! I lived and breathed dinosaurs. Now, I find the Ice-Age period much more interesting. Yes, perhaps the environment was already changing. But the grizzly did, for some length of time, coexist with the Pleistocene megafauna. There is no doubt that he was not the top predator. But a boar grizzly is a tough character in any setting. It is the survival of the she-bears and cubs that would be extremely hazardous in any open country with a heavy predator population. This is the reason, ( IMO ) that most Pleistocene grizzlies of N. America held to more remote locations. But those two grizzly fossils discovered in Oklahoma question how many might have lived in locations that were heavily populated.
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(01-25-2018, 02:39 AM)brotherbear Wrote: Spalea; when I was a kid, I was dinosaur crazy! I lived and breathed dinosaurs. Now, I find the Ice-Age period much more interesting. Yes, perhaps the environment was already changing. But the grizzly did, for some length of time, coexist with the Pleistocene megafauna. There is no doubt that he was not the top predator. But a boar grizzly is a tough character in any setting. It is the survival of the she-bears and cubs that would be extremely hazardous in any open country with a heavy predator population. This is the reason, ( IMO ) that most Pleistocene grizzlies of N. America held to more remote locations. But those two grizzly fossils discovered in Oklahoma question how many might have lived in locations that were heavily populated.

The grizzly probably did witness the downfall of the residual Pleistocene megafauna.

I think grizzly would probably stay away from a starving SF bear, but would indeed try to steal the food from a lone American lion.

Also, the Pleistocene grizzly was about the size of the Kodiak bear or a bit larger.
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United States Polar Offline
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(01-25-2018, 02:39 AM)brotherbear Wrote: Spalea; when I was a kid, I was dinosaur crazy! I lived and breathed dinosaurs. Now, I find the Ice-Age period much more interesting. Yes, perhaps the environment was already changing. But the grizzly did, for some length of time, coexist with the Pleistocene megafauna. There is no doubt that he was not the top predator. But a boar grizzly is a tough character in any setting. It is the survival of the she-bears and cubs that would be extremely hazardous in any open country with a heavy predator population. This is the reason, ( IMO ) that most Pleistocene grizzlies of N. America held to more remote locations. But those two grizzly fossils discovered in Oklahoma question how many might have lived in locations that were heavily populated.

I was (and still kind of) dinosaur crazy too. But I find modern, Eocene, and Pleistocene nature much more interesting, especially with the interactions of bear-like ancestors/bears with other carnivores.
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Switzerland Spalea Offline
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Kid, I was fond of the dinosaurs age too, especially the Cretaceous period (because of the famous T-rex...). But now, imagining some extinct lions and tigers, bigger than the extant ones, struggling with other disapeared species like the short-faced bears, the saber-tooth cats, woollly rhinos, elephants and mastodonts and so on make me even more dream too. Perhaps, I have been simply fascinating by the dinosaurs' dimensions a long time ago, whereas now I can imagine some almost actual and fascinating mammal creatures surviving among other big and monstruous beasts. And also some actual top predators, just a little bigger, in an environment where they weren't top predator.
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United States brotherbear Offline
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We know for sure that Arctodus simus was an apex scavenger. Whether or not he ever hunted and killed his own food is debatable as is just how much vegetation was normally a part of his diet. I see him as a long-distance walker who, once his nose catches the scent of a carcass, could run very fast in a bee-line straight to the source of the scent. It makes sense that he ran camel-fashion and could not zig-zag like a grizzly can. I doubt that the giant ever actually hunted, but he might perhaps have taken an easy meal when available; something that did not require a chase. 
I believe that perhaps the grizzly was therefore more of a hunter than a scavenger, although he did some of both. By hunting, he would have eaten more meat, although in this world, even a big boar grizzly could be displaced from a carcass. Not only from the giant bear, but from a pride of saber-toothed cats or ( if they were also social predators ) by a pride of atrox lions. 
I hope that there will come more fossil evidence which will reveal more of this lost world.
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United States brotherbear Offline
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GrizzlyClaws from post #272... Also, the Pleistocene grizzly was about the size of the Kodiak bear or a bit larger.  
 
I believe this also, but as tigerluver has pointed out, we have no evidence to go on. I do believe that at some point in time, that evidence will be found. I believe that the Pleistocene grizzly was very similar to the California grizzly of the Sierra Nevada. Of course, the size of the bear would still depend on where he lived, environment, food resources, etc. But where food-protein was available in huge quantities, yes I agree.
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This is my idea of a Pleistocene grizzly living out among the Ice Age mega-fauna. Ranging from 4 to 5 feet high at the shoulders ( 1.22 to 1.52 meters ) and weighing from 400 to 1400 pounds ( 182 to 635 kg ) with an average Summer weight of about 800 pounds ( 363 kg ). He would of course be an omnivore and an opportunist. He would probably be more of a predator than scavenger; less competition with the giant.
                                                 
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United States brotherbear Offline
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Interesting Facts: In Europe, the giant cave bear was one of the first Pleistocene mega-beasts to face extinction. In N. America, the giant short-faced bear was one of the last Pleistocene mega-beasts to face extinction.
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United States brotherbear Offline
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twilightbeasts.wordpress.com/2015/01/08/paddingtons-dangerous-cousin/

North and South America were the last continents to be conquered by humans. We have been in Africa since we first evolved, Europe and Asia for over a million years, in Australia for about 60,000 years, but in the Americas for only about 15,000. Considering that reaching Australia required a treacherous ocean voyage but you could walk to Alaska without getting your feet wet via the flat, treeless, mammoth steppe of Beringia (with plenty of game to hunt en-route), why did it take people so long to reach the promised land? Some researchers have suggested that perhaps people did reach Beringia much earlier, but what they met there prevented them from penetrating any further. Along with the mammoths, cave lions, bison, and horses, Beringia had something else. Something that would have been completely unfamiliar to the humans who encountered it. Something seemingly crafted from our deepest, darkest nightmares. Arctodus simus: the giant short-faced bear may have been the most terrifying land carnivore our species ever encountered.
Today, the polar bear (Ursus maritimus) is the largest land carnivore but 12,000 years ago that title went to a member of the subfamily of bears known as the Tremarctinae. We still have one member of this unique subfamily left; the spectacled bear (Tremarctos ornatus). The only bear found in South America (including deepest, darkest Peru), this predominantly vegetarian teddy is technically the largest carnivore left on that continent, despite being a relatively puny 100-200kg. A sister species, the Florida cave bear (Tremarctos floridanus), also roamed Pleistocene North America. However, their close relative, the giant short-faced bears (genera Arctodus and Arctotherium/ Pararctotherium) were absolutely colossal beasts. Arctotherium/Pararctotherium (opinion is divided on how valid these generic distinctions are) has been found all over South America, even down into southern Patagonia. Arctodus simus has been found at sites all over North America, from Alaska and the Yukon Territory down to Florida and Texas. Whilst we have a mitochondrial genome from Arctodus and know it diverged from the spectacled bear during the late Miocene/early Pliocene, it is not known exactly how closely related Arctodus and Arctotherium/Pararctotherium are to each other. Ancient DNA work is happening right now that should give a handle on the complicated phylogenetics of these bears.

Arctodus simus was an 800kg monster. To give some impression of its size: while on all fours this bear could gaze directly into my eyes (I’m 6’2”). Standing on its hind legs an average bear could reach 12-feet (in fact, the site of Riverbluff cave in Missouri has claw marks 15 feet up on some side walls that were probably produced by a large Arctodus). Another site with Arctodus is Big Bear cave in the Ozark mountains. The articulated skeleton found there is impressive for the amount of information it left about short-faced bear biology. The animal, like many other cave finds, was a small female, which cumulatively suggest that Arctodus females denned (perhaps surprisingly, only one fossil Arctodus baculum has ever been recovered). The Ozark skeleton is also unique in the preservation of fossilised hair at the site.
What natural forces could possibly have conspired to produce a carnivore of such enormous dimensions? Most researchers think that the specialisations present in Arctodus (i.e. long legs, large size, short jaws), are adaptations to a life of extreme hypercarnivory. Long legs allow for efficient movement over a wide home range, necessary to locate carcasses, large size can act as an effective deterrent to other carnivores to scare them off a kill site (kleptoparasitism), and short jaws give extra bone crushing power. It seems that this hypothesis is backed up by good data. Stable isotope analysis of Arctodus remains show elevated ∂15 Nitrogen values- this indicates that Arctodus was consuming a very meaty diet, perhaps with a large component of caribou (Rangifer tarandus). However, as with most things in science, different researchers think that the opposite is true and have concluded that the morphology of short-faced bears indicate a life of herbivory with some omnivory. My money is still on Arctodus simus being one of the biggest and baddest animals ever to have lived.  
 
 How badass was it? Well, a very interesting pattern cropped up when palaeontologists were looking at late Pleistocene radiocarbon dates from eastern Beringia. They found that during time periods when Arctodus simus was present (i.e. 20,000-45,000 14C years BP) there is a noticeable lack of other predators (lions, scimitar cats, brown bears). Either the environment was selectively excluding everything but short-faced bears during this time period, or perhaps more likely, Arctodus simus was such an efficient predator/scavenger that there was simply not enough prey biomass left for other carnivores to get a look in. If this was the case, it is perhaps no surprise that human presence in eastern Beringia is only known from after Arctodus’ extinction. Maybe one day we will find an Arctodus coprolite with some evidence of the pre-pre-Clovis pioneers!

Written by Ross Barnett (@deepfrieddna)
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Switzerland Spalea Offline
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@brotherbear :

About #279: Very interesting account ! (as usual...).
But, it's hard to believe the presence of the arctodus simus would provoke the scarcity of the other predators. Especially by taking into account the existence of so numerous great species of big herbivores: American buffalos (which should live in big herds like the extant American buffalos before the white men (coming from Europa) invasion , elephants, elks, deers and so on...
The arctodus simus could it be a so efficient predator ? Or a so efficient scavenger always running through its environment in order to detect any corpse and to frighten any predators around ?
Or rather:
Either was the arctodus simus a very abundant predator, or were the herbivores very scarce too, because of the very harsh life ?
But I don't want to believe that the arctodus simus would have been such a nightmarish beast. The other predators could not be without resources against it, I just imagine several atrox lions, or 2 or 3 dozens of dire wolwes protecting their kills...
Perhaps did the arctodus simus enjoy a superior metabolism ? I joke... I just want to tell that opposed to a very powerful predator the other predators adapt themselves. The only one predator having made the other predators scarce is the human specy. We know why... But here, we are speaking about predator mammals.
I would rather believe that the fossilization conditions weren' t good at all (non-conservative ground or environment).
Perhaps too, the confirmed presence of huge predators would have made very careful the first humans of these lands.
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United States brotherbear Offline
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www.prehistoric-wildlife.com/species/a/arctodus.html

Arctodus - predator or scavenger?
       With such an immense size and obviously powerful jaws it’s tempting to paint a picture of Arctodus as an apex predator that could kill anything it wanted. However, real science is not based upon assumptions that are established upon superficial glances but on in depth study of the available fossil material. With this in mind the analysis of Arctodus remains has led to a surprising but very plausible theory about its nature and behaviour.
       Many Pleistocene mammal fossils have been subjected to a process termed oxygen isotope analysis. This is based upon the principal that different environments have different isotope levels which get absorbed by the plants growing on them. As these plants are eaten the isotopes are absorbed and stored in the herbivores tissues as a marker that allows palaeontologists to establish which types of animal were active in which environment and what they were eating. In turn as these herbivores were killed and eaten by carnivores the isotopes get re-absorbed into the carnivores’ bodies which reveal roughly which animals were being eaten by which carnivores (for example the sabre toothed cat Smilodon seems to have had a preference for bison).
       The analysis for Arctodus shows that it was what is termed a hypercarnivore, an animal that has a diet where seventy to a hundred per cent of the eaten food is the tissue from other animals. However it also revealed that Arctodus ate all kinds of animals, and did not specialise in just one type of prey, something that is highly unusual for a predator, but quite normal for a scavenger.
       The skeleton also reveals hints to both the travelling and predatory ability of Arctodus, with special reference to the long limbs. These could be seen as giving Arctodus a significant reach advantage that allowed it to swipe at prey animals, but the problem here is that first Arctodus would have to get close enough to its prey to do this. In terms of speed the long legs with their broad strides are thought to have given Arctodus a top speed approaching fifty kilometres an hour, something that would have seen it able to comfortably match most of the available prey species.
       However these same legs are proportionally much thinner than they are in other running animals, and are considered too fragile to be able to support a heavy animal like Arctodus if it made a sharp turn when running at speed. This could mean an injury such as a break or dislocation that probably would have been serious enough to cause the death of the injured bear as it could no longer move about. But it is actually these long legs that further support the scavenger theory as since they are lightweight they would not require a great amount of effort to move. Additionally the long sweeping arc of the feet meant that Arctodus could comfortably cover more ground with each step, making locomotion such as walking or even running extremely energy efficient. This means that Arctodus could cover territories that spanned several hundred square kilometres on a reduced amount of food than would be required by a dedicated predator. This is a vital survival adaptation when you consider that a scavenger does not know when or where its next meal is coming from.
       Another clue comes from the immense size of the body. Arctodus simus was the largest carnivorous mammal currently known from Pleistocene North America, and possibly the largest carnivorous animal since dinosaurs like Tyrannosaurus disappeared at the end of the Cretaceous period. As such it’s extremely unlikely that the other Pleistocene predators would have put up much of a fight and risked injury or even death from a more powerful animal. This behaviour has been well documented in modern times where grizzly bears will walk in and steal kills away from packs of grey wolves that let the more powerful predator take what it wants rather than risking injury.

The final support for Arctodus being a scavenger comes from the skull. Arctodus is known as the short faced bear because its snout is proportionately shorter than that of other bear genera. These means that when food is placed in the mouth it is nearer the fulcrum (point of articulation) of the skull and mandible (lower jaw). This focuses a greater amount of pressure from the jaw muscles onto whatever is between the jaws, and seems to have been an adaptation that allowed Arctodus to crack open bones to get at the marrow within them. This is another key survival adaptation as Arctodus would inevitably come across carcasses that had already been picked clean, but the bones still in place because the predators that killed the animal were unable to crunch the bones open. Even more critical to survival is the fact that bone marrow can remain nutritious for months and even years after an animal dies, something that would help Arctodus to survive even when there were no fresh kills to steal. Also fossil evidence of large bison bones exist that look like they have been bitten open by an animal like Arctodus, a feat that would be beyond the scope of smaller predators like wolves.
       Arctodus also had a proportionately large nasal opening in the front of its skull which indicates that it was capable of sampling a larger volume of air for scents. This coupled with the bears larger size meant that it could sniff out and sample scents that were being carried higher up, possibly to the point of detecting a carcass from several kilometres away by smell alone. All of these factors combined point to the short faced bear Arctodus being a much specialised scavenging animal.
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United States brotherbear Offline
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( This post was last modified: 01-31-2018, 03:35 PM by brotherbear )

I believe Artodus and also Arctotherium both to have been omnivores who leaned more heavily towards a meat diet. I view them as perhaps the ultimate kleptoparasite/scavengers.
I will edit and add: I also believe that the Pleistocene grizzly was an omnivore which was more predator than scavenger.
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( This post was last modified: 02-12-2018, 07:35 AM by epaiva )

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Switzerland Spalea Offline
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@brotherbear :

About #281: I thought again the hypothesis you had raised, namely that the Arctodus Simus was a so dreaded predator that it provoked the scarcity of the North America fauna, especially as concerns the other big predators...

That isn't possible because you also noticed an anatomical weakness: he seemed to be unable to swiftly "made a sharp turn " when running at speed. If it is true the other predators would take advantage of it by harassing the ursid during each confrontation around a corpse... And then the ursid's life became impossible. Impossible to sustain such torments. Just try to imagine how, for the Arctodus Simus, it could be hard to endure a pack of wolwes harassing or biting the back of the knees if this was so difficult for him to twirl around at each bite... And I don't evoke lions.

If it was so, the Arctodus Simus sustaining this anatomicla weakness and being a pure scavenger, this ursid had to learn to share the corpses.

If the arctodus being a scavenger needed a reduced amount of food, how could his existence provoke a scarcity of the other predators (American lions, sabertooth cats, wolwes and so on.) ? That is contradictory.

If the Arctodus Simus was a pure predator, the competition would be intensified: the other predators learn to interact with a such powerful, but solitary, opponent.

For these reasons, I think the arctodus Simus wasn't a pure scavenger, and didn't sustain the anatomical weakness you evoked (the life would become impossible for him in that case).

The only things which are able to - naturally - provoke the scarcity of the fauna are the climatic changes. I don't speak about men.
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United States brotherbear Offline
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( This post was last modified: 02-12-2018, 06:28 PM by brotherbear )

Spalea - I agree.
I will edit and add from post #282: I believe Artodus and also Arctotherium both to have been omnivores who leaned more heavily towards a meat diet. I view them as perhaps the ultimate kleptoparasite/scavengers.

I will edit and add: I also believe that the Pleistocene grizzly was an omnivore which was more predator than scavenger.
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