HOW WELL DO THE STABLE HYDROGEN ISOTOPE RATIOS OF BONE COLLAGEN FROM MODERN HERBIVORES TRACK CLIMATIC PATTERNS?

Analyses of the stable hydrogen isotope ratios of bone and tooth collagen from prehistoric herbivores has potential for use as a proxy for reconstructing the hydrogen isotope ratios of surface waters. This, in turn, may yield information about paleoclimatic factors such as precipitation patterns, paleotemperatures, and/or changes in relative humidity. However, before the hydrogen isotopes of fossil herbivores can be used as a precise paleoclimatic proxy, we must first document the degree to which biological factors influence the isotope ratios of animals living within different environments and also among multiple individuals from the same population. We analyzed the stable hydrogen isotope ratios of bone collagen from free-ranging populations of modern bison (Bison bison) and horses (Equus caballus) from North America. Study sites were chosen from a range of climatic and ecological conditions; they represent grassland and shrubland habitats in California, Kansas, Montana, Oklahoma, Nebraska, North Carolina, North Dakota, South Dakota, Utah, and Wyoming. Collagen isotope ratios are compared to variations in mean annual temperature, mean annual precipitation, relative humidity, and the isotope ratios of local surface waters. In addition, we also compare the hydrogen isotope ratios of collagen with analyses of the oxygen isotope ratios of corresponding samples of bone phosphate.