Article: Diagenesis and survival of intracrystalline amino acids in fossil and recent mollusc shells

Amino acid analysis was carried out on intracrystalline organic material from fossil and recent mollusc shells from South Wanganui Basin, New Zealand, ranging in age from 3-6 My old to Recent, absolute abundance of amino acids is highly variable but shows a gradual decline through time due to diagenetic effects. The proportion of peptide-bound amino acids decreases with time, and there corresponding increase in free amino acids as proteins are broken down by natural hydrolysis. By 0-5 Ma, amino acids are free, and the rate of decay of peptide bonds appears to slow appreciably, with proportions of peptide bound amino acids occurring in shells throughout the time span investigated, quantities of free amino acids reach a peak between 0-5 and 1 Ma, after which there is a general decrease in most individual amino acids, presumably because they decay or become incorporated into predominantly insoluble geopolymers. Alanine is a notable exception, increasing in older samples because it is a common product of the breakdown of other amino acids.Amino acid data from different species and from shell beds of different ages were compared multivariate statistical techniques. The results indicate that, despite the effects of diagenesis, the original biochemical distinction between different groups of molluscs (i.e. different proteins within the shell) survives for at least 3-6 My, and may be detectable in older specimens provided sufficient original amino acids remain.