Bears of the Pleistocene

[Ghari Sher]

A little visit back to our tyrant brown bears, as I'll provisionally nickname them.
So a while ago I came across a 2001 PhD thesis by Sarah Elizabeth Collinge (what happened to her since then, I don't know, I can't find a trace of her since this thesis), titled "Body Size and Community Structure in British Pleistocene Mammals", which aimed to estimate the body mass of various large mammal species which existed in the British Isles during the Pleistocene.
https://drive.google.com/file/d/1IH9HeHk...R_USX/view
This includes the brown bear, Ursus arctos, which, according to her, reached their largest size during the Banwell era (identified as MIS 4 in the text, but now known to be the earlier period of MIS 5a).

*This image is copyright of its original author

She estimates a mean weight of 414kg for the bears of this time, with a standard deviation of 187kg.
In the text and Appendix 4.3a, this is broken down to the fact that there is considerable variation in mass estimates for bear specimens from different sites:

*This image is copyright of its original author

She writes:

Quote:Mass estimates from some of the specimens approach 1000 kg, but estimates cover a very large range and imply the occurrence of unusually high sexual dimorphism in this animal. A single humerus specimen from Wretton is also large in size and produces a mass estimate of 440 kg.

-pg. 319

Differences in sex composition at the sites seems a plausible enough explanation, given the high level of dimorphism seen in the brown bear, males being approximately 1.8 times the weight of females, on average. As far as I'm aware they date to the same span of ~20,000 years where this large for of brown bear existed (), though as mentioned the age of the deposits have been shifted slightly.
Assuming the specimens used for the British MIS 5a bears across various sites gave an overall 1:1 sex ratio (unlikely but let's assume) I got average weights of 532kg for boars and 296 kg for sows assuming modern brown bear dimorphism.
AFAIK modern Kodiaks weigh on average about 390kg for males and 210kg for sows, and polar bears 500kg and 227kg for boars and sows respectively.
https://www.bearbiology.org/fileadmin/tp..._Vol_7.pdf
https://www.fs.usda.gov/treesearch/pubs/.../20066.pdf
https://www.researchgate.net/profile/And...ts-Sea.pdf

This would make the tyrant brown bear a very large bear indeed.

BUT

However, I'm a bit cautious to accept those size estimates too readily. While I don't doubt that the MIS 5a brown bears of the UK were very large, I'm not sure if the mass estimates given by Collinge 2001 were accurate, or if they are overestimating to some degree.
According to her she did use extant bear specimens to build regression equations to calculate ursid mass (pg. 137).
But looking at the very large U. a. priscus femoral fragment I mentioned in post #358, the largest in the image, from Skarszyn, I looked at table 8 in Marciszak (2017)'s paper as well as his estimated length of 550-560mm for the complete femur.
Using Christiansen (1999)'s equations, I got weights of 531-562kg for the upper and lower bounds for the femoral length estimates respectively, but using Collinge (2001)'s equations (found in Appendix 3.1.6b) on the lowest estimated FL (550mm), I got a weight of 914kg, quite a bit larger. No other measurements for the Skarszyn femoral epiphysis weight-able by Christiansen (1999)'s are available, but continuing with Collinge's ursid equations:

FL(550mm) 914
FDAW         997
FDAD        1173
Mean -       1028kg

Not sure how plausible it is for the Skarszyn giant to have weighed around a ton, but there seems to be some difference at least between the equations of Collinge (2001) and Christiansen (1999).

Is there anyone here who knows a bit about Ursid mass estimates that might weigh in on this? @tigerluver or @GuateGojira, you've written a bit on felid mass, as far as I can tell, though I'm not sure if you can weigh in on this, or know of any users here who can... if not that's fine. Reply