ABSTRACT
Four species of Recent and Plio-Pleistocene fossil brachiopods were collected from up to 20 horizons spanning the last 2.6Ma of sediment deposition in the South Wanganui Basin, New Zealand, and assayed for the preservation of intracrystalline proteins and/or amino acids. Results indicate that the proteins present in the shells of living and Recent brachiopods undergo rapid degradation through the decomposition of the peptide bond. Up to 80%of the constituent amino acids from the proteins are present in the free state by 0.2Ma, a rate of degradation higher than was originally expected for intracrystalline proteins. Quantitative analysis of concentrations of amino acids present within shells of fossil brachiopods indicate a range of reaction rates for degradation of individual amino acids after decomposition of proteins. Degradation of these amino acids may lead to total loss of compounds, to generation of non-standard amino acids, or to diagenetically-produced proteinaceous amino acids. Such degradation must be recognised for taxonomic considerations to be valid. Principal components analysis demonstrates that, within a horizon, taxonomic discrimination may be completed to at least subfamilial level. A greater understanding of degradative processes should allow a greater level of sensitivity for discrimination.
