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pg 505 Stable isotope analysis was the first isotopic technique used in paleodietary reconstruction (DeNiro and Epstein 1978
Vogel and van der Merwe 1977). One major limitation of stable-isotope analsyses as dietary indication in humans is the liklihood that the tissue analyzed (usually bone collagen) is synthesized by the body from certain fractions of the diet, rather than a mixture of all foods ingested (refs). If these dietary fractionsm e.g., protein and carbohydrate, have differing isotopic compositions, it then becomes important to determine the degree to which these fractions contribute carbon to bone collagen. Unfortunately, the relative contribution of carbohydrate and protein carbon to bone collagen in healthy, normal individuals under different dietary regimes is not generally the subject of metabolic or nutritional research. This is an example of the kind of specialized but currently unavailable data required by paleodietary researchers. pg 506 It is becoming increasingly clear that, unless questions about the origin of the constituents of collagen are addressed fully, isotopic measurements will be limited to qualitative, rather than quantitative statements about dietary composition. Legumes have lower \-15\-N/\-14\-N than other plants because they can fix molecular nitrogen rather than having to rely on nitrates and nitrites in the soil (DeNiro and Epstein 1981). Subsequent studies suggested that \-15\-N/\-14\-N also differentiates marine from terrestrial protein, and may be useful as a trophic indicator (Schoeninger and DeNiro 1084
Schoeninger et al 1983). The exploitation of marine foods is of interest because of complex societies in the Near East and South America. However, new data sets have been developed in the last three years which show that \-15\-N/\-14\-N relations are more complicated than previously thought. pg 508 One central question in paleoanthropology is the importance of meat in the diet of early hominids. Some elements, particularly stronium and barium, are trophic indicators. In a given ecosystem, plants generally have the highest Sr/Ca since they do not discriminant between the two elements. In theory, herbivore bones have lower Sr/Ca than the plants the animals consume. (see Price et al 1985 for review
Sillen Kavanoagh 1982) If plants species vary in Sr/Ca, it comes as no surprise that significant variability also may be seen in the herbivore trophic level (Sillen 1988). Thus, human skeletal Sr/Ca may be determined by Sr/Ca, but this cannot be necessarily be ascribed to the meat-to-plant ratio in the diet. Efforts to understand trace-element diagenesis have become a major them in trace-element paleodietary studies (refs). For example the concentrations of iron, maganese, and aluminum are correlated in interred bone and result from uptake of soil ions rather than biological phenomena (Buikstra et al 1989
Francalacci and Tarlo 1988). pg 509 Marine \+87\+Sr/\+86\+Sr now averages 0.70923 (De Paolo and Ingram 1985), so that in many environments, a clear isotopic distinction exists between marine and terrestrial Sr. The obvious dietary application is the tracing of marine foods where carbon or nitrogen isotopes are found to be inappropriate. \bThe difference in Sr isotopes among geological substrates should make it possivle to srudy the movement of human individuals across these substrates in prehistory (Ericson 1985). This application dependsa upon appropriate geological envrionments and careful choice of skeletal speicmens for analysis. For example, since tooth enamel is not remodeled, its trace elemental and istopic compositions reflect the period of its formation, i.e., youth. On the other hand, bone is remodeled during life, hence its dietary signals probably reflect adult behavior. Moreover, bone remodeling rates vary within skeletons in predictable ways. These observations should enable the investigation of individual life histories, but ultimately will depend more on more-detailed knowledge of remodeling dynamics and regional distributions of SR isotopic ratios.\b
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