Stable Isotope Analysis of Bison latifrons and Paleoecological Inferences

Bison latifrons was a large Pleistocene herbivore that is traditionally hypothesized to have been adapted to living in forest openings and woodlands. According to this view, the species was primarily a browser of high-growing, woody plants. Very little isotopic work has been conducted on this species, and there have been no prior studies of high altitude localities containing this species. This study aims to address both of these issues. B. latifrons is known from sites in several states, including California, Idaho, Colorado, Nevada, and Florida, among others. These sites provide diverse examples of this species’ habitat and the opportunity to collect a robust data set for the purpose of characterizing its paleoautecology. I analyzed carbon and oxygen stable isotopes from tooth enamel to test hypotheses concerning the diet and possible migration patterns of these animals. Data for B. latifrons were collected from a variety of sites, including Diamond Valley Lake, CA, American Falls, ID, and Snowmass, CO. Oxygen isotopic values of meteoric water vary seasonally, with low values occurring in cold months and higher values in warm months. B. latifrons teeth were serially sampled from occlusal surface to root, representing a period of about 18 months and multiple seasons. Seasonal climatic variation within individuals was exhibited in the bison teeth sampled, with the American Falls population subjected to a higher degree of seasonality. The Diamond Valley Lake population possessed a slightly dampened seasonal signal that may be the result of seasonal migration. The signal from Snowmastodon was intermediate between the two. The average δ13C value of B. latifrons in this study was -8.39‰, which is intermediate between a pure C3 browser (approximately -14‰) and pure C4 grazer (approximately 0‰). This indicates that the species was primarily a mixed feeder. This diet was maintained throughout changes in intra-annual climate, as shown by variation in δ18O values. The data also suggest that B. latifrons adjusted its diet based on the different composition of vegetation communities in each site. This is primarily seen in data from the American Falls and Snowmastodon sites, where the populations consumed a higher proportion of C4 plants especially during winter months. B. latifrons at all sites in this study were indiscriminate feeders, eating plant material based primarily on availability