DIETARY BIOMARKERS PRESERVED IN CARBONIFEROUS MAZON CREEK COPROLITE FOSSILS

Carbonate concretions have been found throughout the geological record containing exceptionally preserved soft-tissue fossils and recently are shown to contain biomarkers and biomolecules. The specific conditions which result in growth of carbonate to form concretions also prevent significant decay of organisms prior to encapsulation, resulting in exceptional preservation of soft tissue and lipid biomarkers for up to hundreds of millions of years. Such concretions are abundant in the Carboniferous (306 Ma) Mazon Creek biota, a Konservat Lagerstätte renowned for its diverse assemblage of soft tissue fossils preserved in siderite concretions. Included in this assemblage are coprolites, diagenetically mineralised faeces preserved as three dimensional fossils. Coprolites have the potential to preserve a short-term snapshot of an animal’s diet in the days prior to deposition of the original faecal material.

In this study, lipid biomarker analysis, including stable carbon isotope distributions, and multivariate statistical analysis of in-situ Raman spectroscopy data were combined to analyse two coprolites preserved in Mazon Creek concretions in search of ancient dietary insights. The oldest lipid biomarker and isotopic data obtained from coprolites is presented here and used to determine if the animal, which produced these coprolites, was a herbivore, carnivore or omnivore, offering a new perspective to reconstructing ancient trophic networks.

An exceptionally high abundance of C₂₇ ααα 20R cholestane was present in the fossil of each coprolite, with C₂₇ cholestanes and diacholestanes comprising over 95% of the total steranes content. In contrast the concretion surrounding the fossil showed a much lower abundance of overall steranes. It is interpreted that the steranes distribution of each coprolite fossil likely represents the preserved diet of the coprolite producer. The vast majority of animals are understood to produce exclusively C₂₇ sterols, while higher plants produce primarily C₂₉ sterols. In these coprolites therefore, an overwhelming abundance of C₂₇ steranes and lack of C₂₉ steranes suggests a strong input from animal material with little to no input evident from plants, suggesting that the diets of these animals were carnivorous, or potentially omnivorous.