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Pleistocene Polar Bear v South American Giant Short-faced Bear
Topic Started: Sep 16 2012, 05:53 PM (11,780 Views)
Taipan
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South American Giant Short-faced Bear - Arctotherium angustidens
Arctotherium is an extinct genus of South American short-faced bears within Ursidae of the late Pliocene through the end of the Pleistocene. They were endemic to South America living from ~2.0–0.01 Ma, existing for approximately 1.99 million years. Their closest relatives were the North American short-faced bears of genus Arctodus (A. pristinus and A. simus). The closest living relative would be the Spectacled bear (Tremarctos ornatus). Arctotherium was named by Hermann Burmeister in 1879. It was assigned to Tremarctinae by Krause et al. 2008.[2] A specimen of A. angustidens from Buenos Aires shows an individual estimated, using the humerus, to weight between 983–2,042 kg (2,170–4,500 lb), though the authors consider the upper limit as improbable and say that 1,588 kg (3,500 lb) is more likely, however, using the radious, the mass estimate shrinks to a maximum of 1,108 kg (2,440 lb). Independently of the method it is possibly the largest bear ever found and contender for the largest carnivorous land mammal known to science.

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Pleistocene Polar Bear - Ursus maritimus tyrannus
Ursus maritimus tyrannus was a very large fossil subspecies of the polar bear that descended from an Arctic population of brown bears. Its name in Latin means Tyrant Sea Bear. Initially the isolated brown bears were no different than the variations of brown bears of that time period. Because litters of cubs can show significant species variations in hair color and hair thickness, this gave certain individuals a survival advantage passed on each generation. Eventually skull changes and even changes in dentition occurred leading to the smooth and rather quick evolution of U. maritimus tyrannus. U. maritimus tyrannus was considerably larger then its modern relative. If everything is scaled out correctly from its remains, it would had been 183 cm (6 ft) at the shoulders, 3,6 m (12 ft) long and would have weighted an average of 1.2 tons (Ranging up to an estimated mass of 1,200 kg (2,600 lb)). Its tremendous size makes it even bigger than the other "largest" mammalian carnivores that ever lived, including Andrewsarchus, Agriotherium, and Arctodus simus. It's speculated that this gigantic bear would, due to its formidable size and strength, have preyed on mammoths which also lived during the time.

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yigit05
Sep 15 2012, 11:30 PM
pleistocene polar bear vs arctotherium
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Ursus arctos
Autotrophic Organism

Vodmeister
Sep 17 2012, 05:49 AM
Quote:
 
You haven't justified this statement, especially the qualifier "in the bear world" considering how much evidence we have to the contrary for bears compared to other families.

In the insect world for example, size doesn't mean nearly as much because insects are so different/variant from each other that I've seen many large bugs being killed by smaller ones countless times. For example, I've seen a hornet kill a tarantula much larger.

Another good example would be theropods. I'd favor a Tyrannosaurus over a Spinosaurus, even though the Spinosaurus was about 2.5 times larger. Why? Because the T-Rex, in my opinion, was much better armed and more powerful build than the slender and more fragile Spino. I'm not trying to start a dinosaur debate here.

Bears on the other hand, like felines for example, have all their species & subspecies far too closely build to each other for anything other than size/strength to have any major effect in a face-off. Therefore, the larger bear will almost always prevail over the smaller one, no matter in what way you put it.
Fair enough.
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blaze
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Something else to add, from where the 1200kg estimate comes from? I haven't found a paper mentioning it just this page which doesn't even reference anything.

On "On evolution and fossil mammals" by Björn Kurtén, he compares the ulna in question and while it is very big I don't believe it comes from a 1200kg individual, they refer to it as coming from a subadult individual and compare it to subadult modern bears

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The fragment has a total length of 440mm as preserved. In a very large subadult recent polar bear (UZI No 3), the length without distal epiphyse is 387mm, and the total length 428mm. Thus the full length of the fossil bone may be estimated at a minimum of 485mm.


So, the ulna, is large, 13% larger than... another subadult individual, a very large one at that but I highly doubt it was 850kg for it to be possible to estimate 1200kg for the pleistocene one. It migth be possible that very large adults reached that size assuming the 1002kg record is real but that is speculation and one of which its procedence we don't know, it could of even have originated in a forum like this one.
Edited by blaze, Sep 17 2012, 07:31 AM.
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Vodmeister
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Interesting information from an article I'm sure Ursus has seen/read before:

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Sadly due Imageshack's stupid new policy these pictures will be deleted from being viewed from this site soon enough.
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blaze
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mm it's the only article on Arctotheirum, it brings nothing new

Anyway, I'll vote for the shortfaced bear, because it was larger, the 1200kg for the polar bear came out of nowhere, the ulna probably belonged to an animal no bigger than 400-500kg.
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jj5893
Heterotrophic Organism
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Pleistocene polar bear's coat is thick and could wrestle down walruses and woolly mammoths so it wins.
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dillidar6
Unicellular Organism
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Urus martimus will win because it's stronger and more robust short faced is more closely related to sloth and sun bears than grizzlies both known not to be nearly as powerful pound for pound also saying polar bears are less aggressive doesn't mean much because urus martimus tyranius is a half way link between a grizzly and polar basically it has the predatory skills of a polar with the muscle hump aggression and brute strength of a brown bear.
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predator66
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polar bear wins!
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TheUndertaker45
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Heterotrophic Organism
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Giant short-faced bear wins.Weight advantage.
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Dynasty Warrior
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The short faced bear is to large.
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BoomerSooner
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SA Short faced bear. In my opinion, it was the ultimate carnivore of the pleistocene era. It probably scavenged a lot but it probably would have fought over kills with other predators, such as smilodons (saber-tooth cats).
Edited by BoomerSooner, Dec 15 2013, 07:35 AM.
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Carcharadon
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Both are much smaller than usually portrayed, but arctotherium still has a size advantage so it should win.
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retic
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arctotherium should win this due to its size advantage.
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DarkGricer
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Arctotherium was roughly twice the size of UMT. It's gonna enjoy an easy victory.

SASFB wins 90% of the time.
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Vivyx
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UMT was only 400 kg, the Arctotherium wins almost 100%, if not 100%
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Bob5
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Both of these creatures are enormous, but I think that the short faced bear would win because it is still bigger.
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