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Post by 0ldgrizz on Dec 29, 2014 17:07:31 GMT 5
Two shaggy giants come face-to-face to struggle over dominance of a food source. Very little difference in size here. 
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Post by Infinity Blade on Dec 29, 2014 19:57:14 GMT 5
"Very little difference in size here." Au contraire, there actually IS a difference in size here (a substantial one in fact), even if you took the (exaggerated) weight estimate commonly cited for A. angustidens (which I'm about to address). Someone (namely blaze) can correct me if this was refuted, but M. americanum was ~4 tonnes in mass (hyperlinked). Not even the weight estimates for A. angustidens are that high; the absolute uppermost estimate was ~2,042kg, which was considered improbable (so actually, forget that), ergo a more conservative estimate of ~1,588kg was made (either way, the bear is greatly outsized). And so even then, it's not as anywhere near as large as the sloth. Now onto how that >1.5t weight estimate is exaggerated.  © @ bLAZZE92 (blaze as he is known on here)I'm not an expert on THE nitty gritty on that issue, so if blaze comes by this thread, he can explain it to you better than I could. In any case, an Arctotherium that got into an actual fight to the death with a Megatherium (btw, they both lived in South America during the Pleistocene epoch, so I actually believe this is a sympatric scenario) would be history. |
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Post by 0ldgrizz on Dec 29, 2014 20:43:55 GMT 5
Thanks Macronectes; hope to learn more.
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Post by Infinity Blade on Dec 30, 2014 1:15:16 GMT 5
No problem. |
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Post by theropod on Dec 30, 2014 2:49:32 GMT 5
I’d just love to see a Megatherium skeletal lined up with that bear, simply to see the size contrast!
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blaze
Paleo-artist 
Posts: 766
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Post by blaze on Dec 30, 2014 2:56:13 GMT 5
Yes, 4 tonnes is the largest estimate for Megatherium found in the literature.
About Arctotherium angustidens, there are problems with the 1.6t estimate:
1. The humerus is pathological, with a big projection in its shaft either the result of a healed injury or an infection, this pathology oversized the circumference of the bone and thus any estimate of its mass that uses that measurement.
2. The main equations used to get this estimate suffer from having obese individuals in their sample, two brown bears at 500kg and 680kg that will hardly be 1.1m and 1.2m at the shoulder, such individuals will bias the estimates towards greater weights.
3. Arctotherium, like Arctodus, does appear to have long limbs relative to their body lenght, thus using limb length to estimate their weight based on living ursine bears will overestimate their weight.
I have made an skeletal of Arctodus based on a large and very complete specimen and this is the base for my Arctotherium above which is scaled to the second largest specimen, the biggest one described by Soibelzon and Schrubert (2011) is about 14% larger so about 900kg by GDI, though it could be a litle lower or higher depending on if this bear fattened up for winter or not and if it did, depending on the time of the year.
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Post by 0ldgrizz on Dec 31, 2014 15:13:50 GMT 5
Blaze, would you say that Arctotherium angustidens might have averaged roughly 900 kg ( 1,984 pounds ) which is roughly 1 ton? ( speaking of a mature male of course ) - Summer weight.
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blaze
Paleo-artist
Posts: 766
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Post by blaze on Dec 31, 2014 21:05:04 GMT 5
I think something closer to 800kg was more likely as a summer weight for this specimen* but both are too high as an average for mature males, most Arctotherium angustidens specimens found are old/mature individuals (Soibelzon 2004a) and yet they are far smaller, the one in my skeletal above is too a mature male.
*This lower weight is because previously the outlines I used for the GDI I made them to include fat but later I changed it to only be muscle, the body fat I added it later based on the percentages of brown bears.
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gigadino96
Junior Member
Vi ravviso, o luoghi ameni
Posts: 226 
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Post by gigadino96 on Jan 1, 2015 21:08:11 GMT 5
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Post by Infinity Blade on Jan 1, 2015 22:36:53 GMT 5
That's based on the notion Arctotherium was 1.588 tonnes. |
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Post by 0ldgrizz on Jan 3, 2015 6:54:10 GMT 5
IF Arctotherium angustidens averaged roughly 800 kg at Summer weight, then how would Arctodus simus compare? I have read estimates of this short-faced bear above 800 kg.
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Post by theropod on Jan 3, 2015 17:40:33 GMT 5
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Post by 0ldgrizz on Jan 3, 2015 18:43:13 GMT 5
If the largest Arctotherium weighed 800 kg ( roughly 1,764 pounds ) then he was in the size range of brown bears.
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Post by theropod on Jan 3, 2015 19:19:38 GMT 5
That’d be freak brown bears of the largest subspecies, and Arctotherium is an extinct organism known from far fewer individuals than brown bears.
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Post by 0ldgrizz on Jan 3, 2015 20:14:03 GMT 5
That’d be freak brown bears of the largest subspecies, and Arctotherium is an extinct organism known from far fewer individuals than brown bears. I agree. There were very likely larger individuals of short-faced bears undiscovered. But, of those discovered, and if these weight estimations are correct, then they were within the weight range of the coastal brownies. Those coastal bears are huge due to their diets. Even inland grizzlies can reach 1,000+ pounds if well fed. The giant short-faced bears were without a doubt the largest of bears on average. I'm just seeking what their approximate average weights might have been.
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