Novel Approaches to Ungulate Enamel Isotope Analysis for the Reconstruction of Human Paleoenvironments

Isotopic analysis of fossil ungulate tooth enamel is a popular paleoecological method applied in the reconstruction of human paleoenvironments. Different isotopes provide variable lines of evidence about environmental conditions or animal behavior. Carbon (δ13C) and oxygen (δ18O) enamel isotopes, the two types of isotopes most frequently analyzed in paleontological applications, function as proxies for proportions of woody to grassy plants and aridity in an organism’s environment, respectively. However, the utility of these proxies is dependent on our ability to link enamel isotope ratios to specific environmental or climatic conditions in modern ecosystems to calibrate the approach. As anthropologists, we are most interested in environmental and climactic conditions relevant to questions about the evolutionary environments of both hominins and pre-historic modern humans. In Africa, rainfall seasonality is typically invoked as a key climatic control on the evolution of our lineage, with potential impacts ranging from the emergence of upright posture in the hominoid lineage ~ 21 million years ago (Ma) to the production of microlithic technological suites in the relatively recent archaeological record ~ 18 thousand years ago (ka). Yet, while rainfall seasonality is an important climatic variable to characterize through time in the fossil and archaeological records, well-developed approaches to reconstructing this parameter remain limited. This dissertation aims to develop novel methods to identify paleo-seasonality patterns through the isotopic analysis of ungulate tooth enamel for application to human paleoenvironments. This dissertation investigates the relationships between (1) modern ecosystem type and community enamel isotope signatures and (2) rainfall seasonality and the enamel isotope profiles within ungulate teeth. This research provides critical ground-truthing in modern ecosystems for the interpretation of enamel isotope values both from fossil assemblages and from individual fossil teeth. Furthermore, this dissertation applies a novel application of generalized additive models to the enamel isotope record of terminal Pleistocene southern Africa (40 – 11 ka), allowing for the characterization of variation between sites related to differences in seasonality patterns during glacial and interglacial periods. This work, in addition to establishing a new method of analysis of enamel isotope data, also provided insight into patterns of environmental change occurring during a period of acute climate change ~ 20 ka – the Last Glacial Maximum. This is a time period of keen interest to archaeologists, because of concurrent changes in material culture. These novel approaches to interpreting ungulate enamel isotope data provide new ways to characterize seasonality patterns from the fossil record. Critically, this research facilitates deeper study of the cycling of isotope systems in the highly seasonal environments that characterize geographic regions of the African sub-continent most important to our evolutionary past.