| Description |
Stable carbon and oxygen isotope analysis of tooth enamel is one of the primary tools available for studying terrestrial mammals and ecosystems in the geologic past. Carbon isotope ratios record the proportion of C3 versus C4 vegetation in diet, and by extension, landscape vegetation. Oxygen isotope ratios are related to the isotope ratio of meteoric water and animal physiology and feeding ecology. The carbon isotope ratio in fossil enamel from 9.9 to 3 Ma was measured in ~450 teeth representing nine herbivore lineages to study dietary and vegetation change during this interval in East Africa. Results indicate that differential rates of diet change from C3-dominated to mixed C3-C4 and C4-dominated diets between different lineages began as early as 9.9 Ma. The carbon-14 (14C) concentration in metabolically inert tissues formed since ca. 1955 can be used to determine the date the tissue formed, or tissue growth rate if multiple samples are taken along the tissue growth axis. This method has applications to stable isotope (paleo)ecology and wildlife forensics. 14C-derived growth rates in enamel and tusk dentin elucidate the time represented in periodic growth increments and provide insight into enamel maturation. Changes in the isotope ratios of diet and body water, driven by seasonal variability in vegetation and climate (e.g., precipitation), cause variation in isotope ratios along the growth axis of elephant molars and tusks. Isotopic variation in tusk dentin and tail hair profiles of an extant African elephant are compared. Both profiles serve as a proxy for seasonal changes in vegetation and precipitation. Diagenesis leads to overprinting of the primary isotopic signal in fossil tusks, but not in fossil enamel. However, the process of enamel formation blurs the primary input signal. Combined forward and inverse modeling of intratooth isotope profiles in enamel can be used to reconstruct seasonal variability in diet, vegetation, and climate once appropriate model parameters are established. These parameters are determined for elephant and mammoth molars using 14C data, micro-CT, and histological methods. Application of the models to profiles from fossil proboscidean molar plates provides a means for studying seasonality in ancient ecosystems. |
