oa Diprotodon on Steroids: Reconstruction of It’s Gut Microbiome

Molecular and isotopic analyses of Diprotodon fossils are presently underway to investigate the paleo geobiology of these extinct, giant wombat like animals. The hydrocarbon biomarker composition of sediment from a 48- ka Diprotodon fossil discovered at Lake Callabonna (northern South Australia), included a broad distributions of functionalised and unsaturated steroids. Original sterol biolipids were detected along with a limited suite of diagenetic derivatives (e.g., sterenones, sterenes and steradienes), but no fully saturated or aromatic steroids reflecting the immature nature of the organic matter. The sterol to sterene diagenetic sequence provides another insightful representation of the diagenetic transformation of animal steroids. The ?13C values of C27 sterene (-15.1 ‰ VPDB) and C29 sterene (-22.9 ‰) in gut sediment were consistent with C4 plant sources, varieties of which (e.g. chenopods, euphorbias, saltbush) were prominent within the sparsely vegetated dry salt-lake of Lake Callabonna. The C27 and C29 sterenes are likely representative of animal and plant steroids, respectively, with the approximate +7 ‰ enrichment of the former consistent with a higher trophic level. The ?13C values of C27-C33 n-alkanes (-21.5 ‰ to -24.8 ‰) were similar to the C29 sterene value, suggesting a common plant source.