NICHE PARTITIONING BETWEEN LATE PLEISTOCENE BERINGIAN BISON AND HORSES: NEW INSIGHTS REGARDING DIETARY BEHAVIOR OF HERBIVOROUS UNGULATES ACROSS SPACE AND THROUGH TIME

Megafauna diversity of Pleistocene Beringia was dramatically higher than any modern mammal community in the high-latitudes. In the late Pleistocene, horse, bison, mammoth, musk ox, saiga antelope, and caribou all co-occurred across the Mammoth Steppe. Particularly in regions with limited and highly seasonal resource availability, high faunal diversity is often sustained via dietary partitioning among species. This form of resource allocation may have been especially important for supporting diverse herbivore faunas amidst relatively depauperate floral communities of the far north. Horse and bison were the most abundant herbivores of the Mammoth Steppe and are both considered obligate grazers in modern ecosystems. While this suggests they competed for resources on the North Slope, some dietary reconstructions of Beringian herbivores based on stable isotope data have indicated potential dietary discrimination (the dominance of C₃ plants in northern climates complicates dietary interpretations based on only stable isotope data). Here, we apply Dental Microwear Texture Analysis (DMTA) to assess differences in Pleistocene bison and horse diets from Alaska (carbon dating indicates specimens are from ~50-10 kya) and also compare both to extant taxa with diets consisting primarily of grass in North America and Africa. We find that horse dental microwear textures from Pleistocene Alaska have significantly higher anisotropy values than co-occurring bison, indicating grass-rich diets in the former. Both horses and bison from Pleistocene Alaska have significantly lower anisotropy values than extant zebras. Beringian bison microwear textures have significantly higher complexity values than co-occurring horses, indicating diets that include harder materials such as woody browse. Further, bison from late Pleistocene Alaska have significantly higher complexity and lower anisotropy than extant bison, indicating a diet with a larger percentage of woody browse than today. These results provide evidence for resource allocation among Beringian grazers and support the hypothesis that dietary niche partitioning contributed to a high diversity of Beringian herbivores.