Variation of bone collagen amino acid δ13C values in archaeological humans and fauna with different dietary regimes: developing frameworks of dietary discrimination.

We present bone collagen amino acid (AA) δ(13)C values for a range of archaeological samples representing four "benchmark" human diet groups (high marine protein consumers, high freshwater protein consumers, terrestrial C(3) consumers, and terrestrial C(4) consumers), a human population with an "unknown" diet, and ruminants. The aim is to establish an interpretive palaeodietary framework for bone collagen AA δ(13)C values, and to assess the extent to which AA δ(13)C values can provide additional dietary information to bulk collagen stable isotope analysis. Results are analyzed to determine the ability of those AAs for which we have a complete set, to discriminate between the diet groups. We show that very strong statistical discrimination is obtained for all interdiet group comparisons. This is often obvious from suitably chosen bivariate plots using δ(113)C values that have been normalized to compensate for interdiet group differences in bulk δ(13)C values. Bi-plots of non-normalized phenylalanine and valine δ(13)C values are useful for distinguishing aquatic diets (marine and freshwater) from terrestrial diets. Our interpretive framework uses multivariate statistics (e.g., discriminant analysis) to optimize the separation of the AA δ(13)C values of the "benchmark"' diet groups, and is capable of accurately assigning external samples to their expected diet groups. With a growing body of AA δ(13)C values, this method is likely to enhance palaeodietary research by allowing the "unknown" diets of populations under investigation to be statistically defined relative to the well-characterized or "known" diets of previously investigated populations.