Diet and Co-ecology of Pleistocene Short-Faced Bears and Brown Bears in Eastern Beringia

Abstract

Carbon and nitrogen stable isotope analysis of fossil bone collagen reveals that Pleistocene short-faced bears (Arctodus simus) of Beringia were highly carnivorous, while contemporaneous brown bears (Ursus arctos) had highly variable diets that included varying amounts of terrestrial vegetation, salmon, and small amounts of terrestrial meat. A reconsideration of the short-faced bear's highly derived morphology indicates that they foraged as scavengers of widely dispersed large mammal carcasses and were simultaneously designed both for highly efficient locomotion and for intimidating other large carnivores. This allowed Arctodus to forage economically over a large home range and seek out, procure, and defend carcasses from other large carnivores. The isotope data and this reconstruction of Arctodus' foraging behavior refute the hypothesis that competition from brown bears was a significant factor in the extinction of short-faced bears.