RECONSTRUCTING THE MIGRATION PATTERNS OF PREHISTORIC BISON USING ANALYSES OF TOOTH ENAMEL CARBON, OXYGEN, AND STRONTIUM ISOTOPE RATIOS: IMPLICATIONS FOR PALEOENVIRONMENTAL RECONSTRUCTIONS

Isotopic analyses of prehistoric bison hold good potential for use as a paleoenvironmental proxy because: 1) bison had a wide geographic range, 2) bison remains are common in Holocene and Pleistocene deposits, 3) the oxygen isotope ratios of modern bison are closely correlated with the oxygen isotope ratios of local surface waters and mean annual temperatures, and 4) the carbon isotope ratios of modern bison are closely correlated with changes in grassland vegetation (i.e., the abundance of C-4 grasses) and mean annual temperatures. However, in order to use analyses of bison to reconstruct local environments, we must first determine whether or not prehistoric bison migrated long-distance between different environments. We compared the oxygen and carbon isotope ratios of tooth enamel from subfossil bison from two Late Prehistoric bison jumps located in Wyoming with analyses of modern bison populations from the Northern Great Plains. We also analyzed the strontium isotope ratios of archaeological bison; strontium isotope ratios can be used to identify individuals that migrated from different geologic regions because an animal's strontium isotopes change with changes in local bedrock. The majority of bison at each archaeological site displayed oxygen and carbon isotope ratios that were similar to those of modern bison from the northern Great Plains. However, a few individual at each site displayed oxygen and/or carbon isotope ratios that were significantly different (by up to 5 per mil) from the values of modern bison in this region. Bison with extreme oxygen and carbon isotope ratios also displayed strontium isotope ratios that differed from the mean strontium isotope ratios at each location. These results suggest that: 1) some, but not all, prehistoric bison migrated long distances across different environments, and 2) analyses of multiple isotopic systems can be used to distinguish between migrant and resident animals.