New method for the isotopic study of ancient conchiolin from archaeological shells of freshwater mussels (Unionoida)

Abstract Freshwater mussels shells are common remains in archaeological sites of the Gumelnița culture (5 th millennium BC, Romania), and were part of the diet of its ancient inhabitants. The proteins of these shells are often preserved and can be used for paleodietary and paleoecosystem reconstructions by stable isotopes. To obtain the empirical relationship between the isotopic composition of sell organic matrix and soft tissues, we analysed the body (foot and mantle), the muscle, the conchiolin of the shell and stomach contents of modern individuals of Unio tumidus from the Danube. In addition, modern shells were digested in 5M HCl and archaeological in 1M HCl to obtain the shell organic matrix or conchiolin. We established a quality criterion for freshwater mussel shell conchiolin of 3.6 (± 0.3) for the C:N and obtained an offset of Δ 15 N conchiolin-defatted body = +0.95‰, Δ 13 C conchiolin-defatted body = +0.93‰ for the soft tissues, and an offset of Δ 15 N conchiolin-muscle = +1.7‰, Δ 13 C conchiolin-muscle = +0.3‰ for the muscle. Freshwater mussels from Gumelnița showed that they came from different sources (rivers, lakes, ponds…) but which not necessarily have to come from long distances since all these different habitats were present in the vicinity of the site.