PALEOECOLOGY FROM PROBOSCIDEANS: DEVELOPING A MODEL FOR TOOTH ENAMEL MATURATION IN MODERN ELEPHANTS (LOXODONTA AFRICANA)

Serially sampled stable isotope data from fossil enamel can be used to reconstruct dietary history of individuals and seasonality (e.g., in precipitation and vegetation) in ancient ecosystems. Proboscidean molars are attractive as paleoecological archives for several reasons. The molars are large and relatively easy to sample for isotope analysis, a single molar forms over multiple years, and proboscidean (e.g., Loxodonta spp.) molars or isolated molar plates are found at many Pliocene- to Pleistocene-age East African fossil localities. One factor that complicates quantitative interpretation of serially sampled teeth is the attenuation and blurring of the input signal of carbon and oxygen isotope values due to the process of tooth enamel maturation. To address this problem, we are developing a model for enamel maturation in modern elephant (Loxodonta africana) molars that will allow us to obtain meaningful serial isotope records from fossil proboscideans. We use bomb-curve radiocarbon dating, micro-computed tomography (micro-CT), and serially sampled stable isotope data to evaluate the growth rate and maturation processes in modern elephant enamel. Preliminary bomb-curve radiocarbon data indicate that the last lower molar crown forms over a period of at least 10 and possibly up to 16 years. Micro-CT data show that the initially deposited enamel matrix is approximately 60 to 70% of the density of mature enamel. Hand-drilled oxygen isotope profiles from multiple molar plates of a zoo elephant translocated from northern California to Utah show that the “instantaneous” switch in drinking water is recorded over ~4cm along each molar plate. These data will be applied to a model for enamel maturation that will open the door to interpreting isotope records in proboscidean molars to address questions regarding diet and seasonality in the fossil record.