Bears of the Pleistocene

[tigerluver]

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. 

@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. Reply