Lipids found associated with skeletons represent an important avenue of study in molecular paleontology, because the chemical nature of these compounds means they are often biogenically specific and can survive in the geologic record over millions of years. Though it is clear that these skeletal compounds originate from the mineralizing organism, our understanding of the distributions and nutritional sources of lipids among invertebrates is still limited, requiring that baseline studies of modern taxa be completed to evaluate the potential of skeletal lipids in paleoecological studies.
In this study, skeletal lipids from nine modern invertebrate taxa (five mollusks, a brachiopod, an echinoid, a coral, and a barnacle) were extracted and analyzed. Though the major classes of lipids found in the skeletons are remarkably consistent, the sterol profiles from these organisms contain both dietary and environmental information. The skeletons of filter feeders generally have two to three times the variety of sterols as compared with carnivores and grazers. In addition, specific steroidal contributions from several plant and algal groups (including dinosterol, 22-dehydrocholesterol, and β- and γ-sitosterol) can be identified. The limited nature and distribution of sterols in the carnivore skeleton implies that both sterol-recycling and some degree of molecular selectivity may be occurring in this taxon. Taxa living in nearshore shallow marine habitats have significant sterol contributions from higher plants, while deepwater organisms have relatively little. Since the geologically stable form of sterols often retains the three-dimensional structure necessary to recognize the biological precursor, these compounds may be used for determining the ecology of fossil invertebrates.