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Bears of the Pleistocene
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The European Brown bears from the middle Pleistocene were massive, almost the size of the modern coastal Brown bears.
Some of them can actually be mistaken as the Cave bears. 
UVP015 - The Largest A. simus
 *This image is copyright of its original author  *This image is copyright of its original author Figuerido et al. estimated this specimen to weigh 957 kg based on 4 measurements (tibia length and least medioateral width and femur length and least mediolateral width). There's an issue with this estimate in my mind. The scale factors of body size were very negatively allometric, to be specific, meaning big boned animals would be proportionately lighter. Take femur length for example. Figuerido et al. found a scale factor 2.37, as in longer femurs produce much proportionately lighter animals. Based on observation with other species, I can't accept that. Campione and Evans (2012) found a universal scale factor of a bit more than 2.7 when combining humerus and femur lengths. I've noted that mixing smaller species with larger species causes this slight negative allometry, but when using specific species equation, the humerus and femur are closer to isometry or even positive allometry. Thus, I find it odd that Figuerido et al. found such a negatively allometric scale factor that does not fit either universal or species specific scale factors. I will let the tibia negative allometry pass because cursoriality can possible produce extra long distal long bones, as in the cheetah. But femurs should not have such negative allometry, they are the strongest bone in the body. Thus, I feel Figuerido et al. may have significantly underestimated UVP015. I will use two specimens of Campione and Evans (2012) to show the underestimation: Figuerido et al. equation: mass = 10^(log(femur length)*2.37 - 3.85) Black bear ROM 71435 - Mass = 204 kg, Femur length = 302 10^(log(302)*2.37-3.85) = 107 kg % error = 47.5% Grizzly bear ROM 35699: Mass = 436 kg, Femur length = 445.5 mm 10^(log(445.5)*2.37-3.85) = 268 kg % error = 38.6 % Average % error = 43% You see the issue. The line of prediction seems to have completely missed the trend of bears. More often, false negative allometry predicts smaller specimen well because negative allometry makes smaller specimens proportonately heavier, but this equation did not even estimate the small black bear correctly. @ What do you guys think? Almost forgot the paper, see below. 
Hopefully tonight I will be able to take the time to read and study this information. Thank you much Tigerluver. I have read various articles of both the giant short-faced bears of North and South America. Both Arctodus simus and Arctotherium angustidens are said to have a bipedal height of roughly 11 feet. I have therefore concurred that the size difference is in their mass while being roughly equal in height and length. Would you agree?
Another interesting Pleistocene bear was Ursus maritimus tyrannus. This intermidiate bear between the grizzly and the polar bear might have been the biggest member of the Genus Ursus ever. Some "experts" believe him to have been more grizzly-like than polar bear-like in appearance and habits. Some disagree. Exactly what is really known about this mystery bear? How does he measure up to the giant cave bear and the short-faced giants?
The largest U. m. tyrannus is a fragmented ulna estimated to be no less than c. 485 mm by Kurten (1964) in length. The largest polar bear male published in the same work has a 428 mm. The largest A. angustidens ulna is 570 mm and the largest 591 mm for A. simus if I'm not mistaken.
Small sample size for U. m. tyrannus, no doubt, but it still seems well outclassed by the giant short-faced bears. Averaging the ulna lengths of the 6 males in Kurten (1964) and assuming these males average 450 kg and ulna scales isometrically, this specimen would would around 860 kg. Issue is, the ulna is a distal long bone and often lengthens for locomotion rather than mass, and if U. m. tyrannus is not a carbon copy of the modern polar but rather more cursorial, this specimen would be lighter than 860 kg. The width measurements for fossil ulna show a specimen either as robust or a bit less robust than the modern polar bears, so 800 kg may be more likely. Use this link to read Kurten (1964): The evolution of the Polar Bear, Ursus maritimus Phipps One last thing, seeing the 591 mm ulna for A. simus, and comparing it to A. angustidens 570 mm ulna, which is from the same specimen whose 620 mm humerus gave it the title of heaviest bear, this title is again brought into question. I've already gone over the femur issue, and now this A. simus ulna produces a humerus of no less than 640 mm assuming equal proportions.
If these estimations are correct, and if these fossils are from an average specimen of Ursus maritimus tyrannus, 800 kg = roughly 1,764 pounds. Not as big as the giant short-faced bears, but still a huge bear. But of course, this is a lot of ifs.
Giant Cave Bear - Ursus spelaeus ~
 *This image is copyright of its original author
Bite force of the extinct Pleistocene Cave bear Ursus spelaeus Rosenmüller from Europe by Aurora Grandal-d’Anglade
Key points:
 *This image is copyright of its original author  *This image is copyright of its original author
Is the bite force of the giant cave bear equal to that of the giant panda in actual size or parity?
In relative terms, so N/cm. In terms of just raw force N, the male U. spelaeus have the greatest bite force.
 *This image is copyright of its original author U. m. tyrannus' ulna. It has some unique shape features such as the consistent thickness of the shaft but I can't discount intraspecific variation.
Thank you tigerluver. This really puts things into perspective. Of course, you could have tossed in the polar bear, the giant cave bear, and Agriotherium africanum; but there is such a thing as over-doing a project. I greatly approve of your choices. It appears that both of the giant short-faced bears can share the title of "biggest bear ever."
@
A while back I stated I would discuss the morphological differences between A. simus and A. angustidens. Before I start, I'd like everyone to see a visual comparison of specimens of each species. The bones are artificially scaled to the same length to make it easier to discern proportional differences.
 *This image is copyright of its original author  *This image is copyright of its original author  *This image is copyright of its original author Will post the sources, actual measurements, ratios, and the rest soon. Until then, I'd like to hear your thoughts on what you see in terms of differences between the specimens. |
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