Chimera of fossil biomolecules found in Pleistocene fossil in tropical cave: Fossil biofilm characterization by micro Raman spectroscopy

Abstract

Finding biomolecules in fossils is a challenging task as they tend to degrade over time due to physical, chemical, and biological factors. The primary hypothesis explaining the presence of biomolecules in fossilized bone suggests that they were preserved during the fossilization process. Some studies posit that these biomolecules may result from contamination by bacteria biofilm formed during fossilization, or they could be artifacts arising from measurement procedures. Several studies on the fossilization process, covering diverse fossil ages and environmental conditions, have used Raman spectroscopy. They report the detection of multiple bands between 1200 to 1800 cm-1 associated with organic compounds, yet a complete understanding of the significance of these bands remains elusive. Our aim is to address this issue through Raman spectroscopy investigations on Pleistocene teeth from Tayassu and Smilodon populator. These fossils were obtained from a well-preserved stratigraphic sequence in Toca de Cima do Pilão cave, near the National Park of Serra da Capivara in semiarid Brazil. We propose two hypotheses to explain the presence of organic compounds in fossil bones: i) these compounds serve as biological signatures related to preserved fossil biomolecules, or ii) they are biological signatures associated with the formation of bacterial biofilm. Our results align with the second hypothesis, showing that these organic signatures are linked to biofilm formation, with a high likelihood of biofilm degradation. However, the specific mechanisms involved in the natural degradation of biofilm in fossil records remain unexplored in this study. In our case, the formation of biofilm on fossil bones is attributed to the oligotrophic conditions of the cave sediment matrix. We present a comprehensive model to elucidate the existence of biofilm on fossil bones, emphasizing the pivotal role of post-depositional processes, especially water action, in the cave environment. As the fossils were discovered in a cave setting, post-depositional processes significantly contribute to the formation of the biofilm matrix. Although our study provides insights into biofilm formation, further research is needed to delve into the specific mechanisms driving natural biofilm degradation in fossil records.