Three case studies used to reassess the reliability of fossil bone and enamel isotope signals for paleodietary studies Julia Lee-Thorp a, * and Matt Sponheimer a,b a Department of Archaeology, Faculty of Science, University of Cape Town, Private Bag, Rondebosch 7701, South Africa b Department of Anthropology, University of Colorado at Boulder, Boulder, CO 80309, USA Abstract 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 KruegerÕs 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 13 C/ 12 C, 18 O/ 16 O, 87 Sr/ 86 Sr, 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 Ôenamel-likeÕ crystallisation changes. Ó 2003 Elsevier Inc. All rights reserved. Keywords: Makapansgat; Border Cave; Reunion Rocks; Bone chemistry; FTIR; Paleodiet; Carbon isotopes; Oxygen isotopes; Strontium isotopes Introduction Twenty years ago Sullivan and Krueger published a seminal paper that pointed the way to routine use of the mineral phase of calcified tissues (Sullivan and Krueger, 1981) for dietary isotope studies. Using bone samples previously obtained from archaeological sites for ra- diocarbon dating, they showed that stable carbon iso- tope values extracted from a vigorously purified mineral phase were offset, but comparable in reliability, to values extracted from the purified organic phase (Fig. 1). All of their samples ranged in age from recent to just over 20,000 years. Their findings were challenged on the grounds that mineral derived from other bones associated with fairly recent archaeological sites in Peru and Mexico did not yield similarly consistent results and seemed to be ir- reparably altered (Schoeninger and DeNiro, 1982). Al- though some questions arose about the comparability of the two sets of results, related to differing pre-treatment procedures and the effects of trophic level on the offset, the net effect was to cast carbon isotope values extracted from the mineral phase under suspicion. This general view was partially reversed when results of a study of consistent C 3 -feeders showed that only small shifts oc- curred in their bone d 13 C values over time (Lee-Thorp and van der Merwe, 1987). The results, however, seemed far more reliable for enamel, and it was this observation that was picked up and subsequently acted upon. A modelling study (Wang and Cerling, 1994) reinforced Journal of Anthropological Archaeology 22 (2003) 208–216 www.elsevier.com/locate/jaa * Corresponding author. Fax: 27-21-6502352. E-mail address: jlt@science.uct.ac.za (J. Lee-Thorp). 0278-4165/$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0278-4165(03)00035-7