The total amino acid content of fossil pecten shells.

Amino acid analyses have been made of the insoluble protein, soluble peptide, and free amino acid fractions isolated from a series of fossil pecten shells of ages from the Pleistocene through the Jurassic. The total amino acid content declines progressively with age of the fossil but, in contrast to oyster shells, only a small fraction of the initial protein is present in the Pleistocene and older specimens. Though the thermally less stable acids are depleted in the free acid fraction, this is not true for the insoluble proteins and peptides. Large amounts of free amino acids and peptides persist through the Pliocene, considerable quantities of peptide have been recovered from the Miocene specimens, and even the oldest fossils have retained analyzable amounts of all three fractions.