Bears of the Pleistocene

[brotherbear]

The shrinkage of brown bears - www.allgrizzly.org/
 
One interesting parenthetical observation about brown bears is that they seem to have diminished in size over the course of the last ice age (the Pleistocene). This was first observed by Bjorn Kurten, a world-famous Finnish paleontologist, based on measurements of fossil brown bear skulls collected in Europe.
 
More recently, Adrian Marciszak and associates published results, also based on measures of bear skulls found in Europe, that seem to have pretty much nailed this trend. These results are summarized at left, arrayed according to time, from left to right, differentiating males from females and measures of skull length from skull width. (The acronym MP refers to "middle Pleistocene," progressing in time to the recent, "R"). One feature of these results is the suggestion that males dwarfed more substantially than did females.
 
This begs the question: Why? Hemispheric patterns in the size of contemporary brown bears (see Morphology) suggest that bears are larger where they eat more protein, typically in the form of meat. There was certainly a lot of meat around during the Pleistocene, perhaps in the form of carrion able to be obtained from the carcasses of the numerous large herbivores dying from any number of causes (see History). According to Herve Bocherens, an expert on reconstructing diets from the analysis of ancient tissues, brown bears were especially carnivorous during the Ice Age, especially in the steppe tundra of Eurasia. This is all consistent with the larger size of Ice Age brown bears being a consequence of ingesting more meat. Even the differences between trends in male and female sizes is consistent with a meat effect given that males tend to eat comparatively more meat whenever it is available, which means they would have been comparatively more affected by the rapid decline of the meat resource caused by widespread extinctions of the large herbivores towards the end of the last Ice Age. Reply