INVESTIGATING THE ECOLOGY OF EXTINCT PROBOSCIDEANS FROM THE CINCINNATI REGION USING STABLE ISOTOPES

Like their modern African relatives, the extinct proboscideans of North America likely played important ecological roles, including maintaining open grasslands. Yet, the degree to which these animals utilized different plant resources and moved across the landscape has not been comprehensively investigated in North America. We used stable carbon (δ¹³C), oxygen (δ¹⁸O) and strontium (⁸⁷Sr/⁸⁶Sr) isotopes from tooth enamel to investigate the ecology of four mastodons (Mammut americanum) and eight mammoths (Mammuthus spp.) from southwestern Ohio and northwestern Kentucky. We also examined ⁸⁷Sr/⁸⁶Sr ratios in regional water bodies. We aimed to answer the following questions: Did these mammoths and mastodons have different dietary regimes? Were these proboscideans local residents or simply passing through the region when they died? If passing through, from where did they come?

Based on tooth morphology and previous isotopic work, we expected that mammoths and mastodons would have differing δ¹³C values, indicating C₄ grazing and C₃ browsing niches, respectively. We compared ⁸⁷Sr/⁸⁶Sr ratios in waters and proboscideans tooth enamel to identify local residents and potential migrants. We then used δ¹⁸O values to pinpoint possible origins for migrant individuals. As anticipated, mammoths have significantly higher δ¹³C values than mastodons. This suggests that mammoths may have consumed more C₄ grasses, although one mammoth has δ¹³C values suggesting a C₃-based diet. Overall, strontium isotope ratios for proboscideans and local waters are indistinguishable. However, one Mammut molar has significantly higher ⁸⁷Sr/⁸⁶Sr ratios, suggesting this animal immigrated into the area from somewhere outside of the Midwest. Combined ⁸⁷Sr/⁸⁶Sr and δ¹⁸O values suggest this animal may have migrated from the southern Appalachians. These results will supply a foundation for future work on proboscideans and other extinct megafauna from the Midwestern United States.