Prospects for Sterane Preservation in Sponge Fossils from Museum Collections and the Utility of Sponge Biomarkers for Molecular Clocks

Abstract

Abstract The sponge biomarker hypothesis argues that 24-isopropylcholestanes preserved in Neoproterozoic-age rocks are “molecular fossils” left behind by marine sponges. Despite genetic and geologic support for this hypothesis, 24-isopropylcholestane has never been reported from a sponge body fossil. This lack of direct evidence regarding the source of sponge biomarkers through deep time leaves unanswered questions, such as whether their biosynthesis evolved once in sponges or multiple times across different lineages. In this study, we analyzed 10 sponge fossils from the Yale Peabody Museum of Natural History collections in pursuit of evidence of sterane biomarkers. We failed to recover 24-isopropylcholestane and instead found a near-identical sterane profile across all samples. This result indicates a combination of little to no sterane preservation in the fossils themselves, coupled with anthropogenic hydrocarbon contamination during their collection and storage. However, signals from bacterial biomarke...