Degradation of intracrystalline proteins and amino acids in fossil brachiopods

Four genera of Recent to Plio-Pleistocene articulated brachiopods were collected from up to 16 horizons spanning the last 3.3 Ma of sediment deposition in the South Wanganui Basin, New Zealand, and assayed for the preservation of intracrystalline proteins and/or amino acids. The proteins present in the shells of living and Recent brachiopods undergo rapid degradation through the decomposition of the peptide bond. Up to 95% of the constituent amino acids from the proteins are present in the free state by 0.12 Ma. This rate of degradation is far higher than was originally expected for intracrystalline proteins. Quantitative analysis of the concentrations of amino acids present within the shells of fossil brachiopods indicates a range of reaction rates for the subsequent degradation of individual amino acids. The degradation of these amino acids may lead to the total loss of compounds, to the generation of non-standard amino acids, or to diagenetically produced proteinaceous amino acids. These reactions do not necessarily mirror those which occur during the pyrolysis of an aqueous solution of the pure amino acids, either in their rate or products.