Molecular and isotopic compositions of lipids in bivalve shells: A new prospect for molecular paleontology

Abstract

Recent and fossil bivalve shells contain suites of lipids that include fatty acids, cholesterol, phytadienes, ketones, and in some cases, n-alkanes. Compound-specific carbon isotopic analyses of fatty acids in shells of chemosymbiotic and heterotrophic bivalves suggest that some of the fatty acids are derived from the animal during biomineralization, although it appears that several independent biosynthetic pathways are used by the clams for the production of these fatty acids. In addition, several compounds, including cholesterol, detected in the shells have similar carbon isotopic values, regardless of the trophic strategy of the bivalve, suggesting that both bivalves derive these compounds from an external, heterotrophic source. Fossil shells contain similar suites of lipids, although in lower relative concentrations. The discovery of diverse lipids in shells opens new avenues for studies of molecular paleontology by taking advantage of the structural diversity and long-term stability of these compounds.