Three case studies used to reassess the reliability of fossil bone and enamel isotope signals for paleodietary studies

The emphasis on tooth enamel for extraction of stable light isotope signals from the mineral phase of archaeological and paleontological calcified tissues is based on the widespread understanding that enamel remains a relatively closed system, while bone does not. Twenty years ago, however, Sullivan and Krueger's groundbreaking study demonstrating the potential of stable carbon isotopes from the mineral phase relied entirely on bone apatite samples from archaeological sites. Further effort to test whether diagenetic effects in bone mineral may be circumvented remains important because bone apatite yields dietary information about adult life-stages beyond the discrete snapshots obtainable from enamel. In this paper we re-examine the grounds for exclusion of bone apatite as sample material, using case studies drawn from three sites which differ in age and depositional conditions. We use C-13/C-12, O-18/O-16, Sr-87/Sr-86, and Fourier transform infrared (FTIR) spectroscopy data from three sites (Reunion Rocks, Border Cave, and Makapansgat Limeworks) to show that, while enamel is not a closed system, it nevertheless retains biogenic isotopic signals. In addition, bone signals may be surprisingly well preserved where fossilisation pathways have induced 'enamel-like' crystallisation changes. (C) 2003 Elsevier Inc. All rights reserved.