BISON LATIFRONS WAS A MIXED FEEDER: ISOTOPIC ANALYSIS OF TOOTH ENAMEL

Bison latifrons was a large, North American, Pleistocene herbivore that has long been hypothesized to have been adapted to living in forest openings and woodlands. According to this view, the species was primarily a browser on high-growing woody plants. To test this hypothesis, we analyzed stable carbon and oxygen isotopes from B. latifrons tooth enamel from four localities: Diamond Valley Lake, CA; American Falls, ID; Snowmass, CO; and west-central Florida. These localities represent a wide range of elevations and ecological settings.

We sampled the teeth serially, choosing M3/m3 teeth where possible. While serial sampling may not provide a precise seasonal signal, distinct annual variation is present in the oxygen system and also in our data. δ¹⁸O values in meteoric water vary seasonally, with lower values occurring in cool winter months and higher values in warm months. Seasonal climatic variation within individuals was exhibited in the bison teeth sampled, with the American Falls population reflecting a higher degree of seasonality than populations at the other sites. The Diamond Valley Lake population possessed a slightly dampened seasonal signal that may be the result of seasonal migration. The signal from Snowmass was intermediate between American Falls and Diamond Valley Lake. Data from Florida confirm a much warmer climate than any of our other sites, with a low degree of seasonality.

The average δ¹³C value of B. latifrons in this study is -6.41‰, which is intermediate between a pure C₃ browser (-14‰) and a pure C₄ grazer (0‰). This indicates that B. latifrons at all sites in this study was an indiscriminant feeder, eating plant material based on availability. This diet was maintained during inter-annular variations in weather, as shown by the variation in δ¹⁸O values. The data also suggest that B. latifrons adjusted its diet based on variations in the composition of the plant community at each site, especially during the winter. The relict population from Florida exhibits a generally enriched δ¹³C signal, suggesting that the animals predominantly fed on C₄ material. These results contradict the long-held assumption that B. latifrons was a browser; it suggests that the diet and habitat were more malleable than previously assumed.