SEASONALITY OF MAMMUT AMERICANUM FROM THE LATE PLEISTOCENE OF WEST TENNESSEE

Serial sampled stable oxygen isotopes (δ¹⁸O) in mammalian enamel record environmental conditions experienced by an individual over the period in which the enamel mineralized, usually reflecting the local precipitation and temperature. Serial sampled stable carbon isotopes (δ¹³C), meanwhile, reflect seasonal patterns of vegetation consumed or the habitat occupied by the mammal over the same period. For animals living in regions with a strong seasonal signal or encountering a wide range of habitats, reconstructions of annual cycles can display significant changes in δ¹⁸O and δ¹³C. Modern proboscideans (e.g., Asian and African elephants) inhabit large geographic ranges (>1000 km) and encounter a wide variety of habitats with strong seasonal selectivity in food sources and climatic conditions. However, the extent to which Late Pleistocene proboscideans encountered similar conditions is not well known. In particular, seasonal cycles of the American mastodon (Mammut americanum) have not received thorough investigation through sampling of molar enamel. Although mastodons are presumed to have inhabited large geographic ranges due to their reproductive and dietary requirements, their ecological role as specialized closed forest-dwelling browsers may have limited the range of resources they were capable of exploiting.

To investigate the habitat and dietary preferences of mastodons, we serially sampled 3 molars (1 third molar, 2 second molars) of three separate individuals of Mammut americanum for stable oxygen and carbon isotopes. Molars were found in the Peoria loess of West Tennessee - sediments corresponding to the Last Glacial Maximum. We found minimal variation in the stable carbon isotope signature, although a minor cyclical pattern in δ¹³C_PDB (on the order of 0.2 – 0.4‰) may reflect seasonal supplementation of herbs and/or mosses. We also found minor fluctuations in δ¹⁸O_SMOW (1.0 – 3.0‰) which may be coincident with a weak wet/dry or warm/cold seasonal cycle, although it might also reflect mastodon reliance on buffered water sources. Our study is notable in that it represents the first attempt to assess proboscidean foraging strategy over time and space on Pleistocene proboscidean material from Tennessee.