A novel marine dietary indicator utilising compound-specific bone collagen amino acid δ13C values of ancient humans

The application of bone collagen stable carbon and nitrogen isotope analysis to human palaeodietary reconstruction in tropical or arid regions is limited by two factors: (i) the overlap in C4 and high marine protein (HMP) consumer bulk collagen d 13 C values, and (ii) the unpredictability of bulk collagen d 15 N values in regions of extreme aridity (!400 mm of rain per annum). Hence, the identification of HMP consumption among archaeological human populations can be problematic. In an endeavour to identify a more precise marine palaeodietary indicator, a range of collagen samples from archaeological faunal and human bone (n ¼ 14 and 26, respectively), representing a spectrum of C3 ,C 4 and HMP diets, were selected from coastal and near-coastal sites in the Western Cape, South Africa. Samples were subjected to compound-specific stable carbon isotope analysis of their constituent amino acids as trifluoroacetyl-isopropyl (TFA-IP) esters via gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). While human C4 and HMP consumers were indistinguishable with respect to bulk collagen d 13 C values (� 10.9G3.7& and � 11.7G1.5&, respectively) they were shown to be readily distinguished based on D 13 CGlycine-Phenylalanine values (C4.0G1.6& and C12.0G1.9&, respectively). The relationship between HMP consumption and elevated D 13 CGlycine-Phenylalanine values was verified by: (i) the similarly elevated values exhibited by marine species when compared to terrestrial faunal species (C12.5G0.9& and C3.2G4.2&, respectively), and (ii) the strong correlation observed between human D 13 CGlycine-Phenylalanine and bulk collagen d 15 N values (R 2 ¼ 0:83, p!0:001; n ¼ 26), the latter being a well-documented marine dietary indicator. It was concluded that D 13 CGlycine-Phenylalanine values offer considerable potential as indicators of HMP consumption and a valuable substitute for bone collagen d 15 N values in arid regions where bulk d 15 N values are unpredictable.

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