Figure 10. Comparison of the amino acid composition of the shells Recent and fossil representatives of Calloria inconspicua. The protocol for the extraction and analysis of intracrystalline amino acids from fossils is described in full in Curry et al. 1991. In this case the amino acid data were obtained in replicate following manual hydrolysis using an ABI 420H Amino Acid Analyser. Letters on the horizontal axis refer to the different amino acids (see below for key), and the data are presented in mole percentages. For most amino acids the relative proportions found in fossil shells has declined. The exceptions are Glycine and Alanine, which are more abundant in the fossil; the relative proportion of these small amino acids increases in fossils because they are formed by the breakdown of other less stable amino acids (which is common in fossils – see Curry et al. 1991).