Bears of the Pleistocene - Printable Version

Bears of the Pleistocene - Printable Version

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RE: Bears of the Pleistocene - GrizzlyClaws - 11-05-2015

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.

RE: Bears of the Pleistocene - tigerluver - 12-07-2015

UVP015 - The Largest A. simus

*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.

@~~brotherbear~~'s request for a prehistoric bear comparison drove me to this investigation. When reconstructing body size based on full skeletons, I found that UVP015 would reconstruct to a shoulder height of 1850 mm. A. angustidens largest 620 mm humerus would reconstruct to 1800 mm. The wrong one is larger according to the traditional school of thought, so I had to reinvestigate.

What do you guys think?

Almost forgot the paper, see below.

RE: Bears of the Pleistocene - brotherbear - 12-07-2015

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?

RE: Bears of the Pleistocene - brotherbear - 01-05-2016

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?

RE: Bears of the Pleistocene - tigerluver - 01-06-2016

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.

RE: Bears of the Pleistocene - brotherbear - 01-06-2016

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.

RE: Bears of the Pleistocene - brotherbear - 01-09-2016

Giant Cave Bear - Ursus spelaeus ~

*This image is copyright of its original author

RE: Bears of the Pleistocene - tigerluver - 01-10-2016

Bite force of the extinct Pleistocene Cave bear Ursus spelaeus Rosenmüller from Europe by Aurora Grandal-d’Anglade

Key points:

Male specimens have stronger bite force than females as expected, but relatively, the two are equal.
U. spelaeus carnassial bite force is similar to the giant panda, greater than the polar bear, and less than the lion and the tiger.
The polar bear probably has a weaker bite force due to its relatively recent evolution.

Key tables:

*This image is copyright of its original author

RE: Bears of the Pleistocene - brotherbear - 01-10-2016

Is the bite force of the giant cave bear equal to that of the giant panda in actual size or parity?

RE: Bears of the Pleistocene - tigerluver - 01-10-2016

In relative terms, so N/cm. In terms of just raw force N, the male U. spelaeus have the greatest bite force.

RE: Bears of the Pleistocene - tigerluver - 01-10-2016

*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.

RE: Bears of the Pleistocene - tigerluver - 01-26-2016

*This image is copyright of its original author

RE: Bears of the Pleistocene - brotherbear - 01-26-2016

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."

RE: Bears of the Pleistocene - tigerluver - 01-26-2016

@~~brotherbear~~, I actually plan to add on more species, but I took so long to get this done, I decided to post it anyhow. Though, for some reason the polar bear slipped my mind, good reminder.

RE: Bears of the Pleistocene - tigerluver - 01-29-2016

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

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.