Intra-tooth isotope variations in late Miocene bovid enamel from Afghanistan: paleobiological, taphonomic, and climatic implications

The rich mid-Turolian site of Molayan (Afghanistan) has yielded more than 100 mandibles from the bovid Tragoportax afghanicus. In this study we document different aspects of the paleobiology and paleoecology of this fossil bovid by examining patterns of inter- and intra-tooth carbon and oxygen isotopic analyses in M1 to M3 molars from five specimens. Accurate paleoecological and paleoclimatic inferences based on carbon and oxygen isotope analyses in fossil enamel are directly dependent upon the way in which teeth are sampled as well as taphonomic processes which are responsible for fossil accumulation. Because this sampling methodology provides a unique opportunity to detect seasonal changes in diet and environment during tooth formation, it also offers the possibility of testing between catastrophic and progressive deposition at this site. Preservation of δ13C and δ18O values is shown to be good and permits inter-individual comparisons of isotopic trends to be made. Timing of molar crown formation and enamel growth rate were deduced from the pattern of intra-tooth carbon and oxygen isotope variation. The pattern of δ18O variation found in the first and second molars is similar in all the individuals, which suggests that a single birth season occurred probably before the hot/dry season. Large differences in average δ18O values (>2.5‰) are found within a single cohort and indicate that fossil accumulation was progressive rather than catastrophic. The hypothesis that T. afghanicus evolved in an open environment is supported by high δ13C values in a C3 context. Increasing temperature and/or aridity eastward along the Greco-Irano-Afghan biogeographic province is strongly suggested by increasing δ18O values between Greece and Afghanistan.