RUMBLE IN THE PLEISTOCENE: BISON LATIFRONS PALEOECOLOGY AND MEGAFAUNAL COMPETITION

The paleoecology of North America may be studied through a combination of climate proxies and paleontology. Identification of megafaunal distribution is useful in determining the character of a region, and isotopic analysis of a single taxon leads to a higher resolution study.

Bison latifrons was a Late Pleistocene megaherbivore which inhabited the Great Basin and Great Plains regions of North America, with a temporal range between the Illinoian and Wisconsin glacial periods (130 – 85 ka). The taxon was previously assumed to have been adapted to forested environments, where it would have competed for resources with Mammut americanum. An alternate hypothesis suggests the bison inhabited the open areas of the Great Plains, and primarily competed with Bison antiquus. The data gathered in this study strengthen the understanding of the paleoecology and interactions of these species.

The assemblages sampled in this study are located in California, Colorado, Idaho, and Nevada. The use of carbon and oxygen stable isotopes determines whether there is a migration pattern visible in the populations studied. Oxygen data positively correlate with the locality of the sampled animals, while significantly offset δ¹⁸O values are characteristic of a herd with different origins. A large shift in δ¹³C value throughout the same site suggests a change in diet, possibly attributed to seasonal migration.

Data from Snowmass, Colorado were unexpectedly positive, and suggest a diet of exclusively C₄grass, or diagenesis has occurred. A positive covariance between oxygen and carbon values suggests the same degree of diagenesis in both isotopic systems.

Data from American Falls, Idaho had averages of δ¹³C -7.72 and δ¹⁸O -9.22 ‰ VPDB. Carbon data indicate mixed feeding with a preference for C₄ grass, suggesting the animals spent more time in open fields than previously thought. Seasonality is a possible cause for the covariation in several teeth sampled. δ¹³C values increase as the amount of C₄ plants consumed increases, while δ¹⁸O values become more negative as a function of decreasing temperature.

Further data from the Diamond Valley Lake assemblage in Hemet, California are placed into context with our previous findings. Based on multiple assemblages, B. latifrons is characterized as an opportunistic browser which preferred open habitats.