PHOSPHATIZED BACTERIAL FOSSILS PRESERVED IN LATE TRIASSIC COPROLITES FROM POLAND

Abundant, micrometer-sized (up to 3μm) and well-preserved spherical structures were detected in numerous coprolites found in the Upper Triassic terrestrial deposits of Silesia (southern Poland). The phosphatic composition, tooth, fish scale and bone inclusions within some of them suggest that they were produced by predators, most probably large temnospondyl amphibians and archosaurs (phytosaurs, rauisuchians and theropod dinosaurs), the remains of which were also detected in the coprolite-bearing deposits. The structures reported, most probably microbial in origin, form the main mass of the coprolite matrix. These structures are very similar to both modern and other fossil bacteria preserved in phosphatic coprolites. Like the other known examples, also those reported here were probably fossilized by precipitation of phosphate within the periplasm of the cells. Therefore, the microbes and microbially-induced phosphatization was certainly responsible for the phosphatization of coprolites studied.

Detailed analyses of the coprolites and preserved bacterial structures are currently under way. However, the preliminary organic geochemical data shows the occurrence of organic matter in coprolites (TOC = 0.4 to 1.5% ), thermally immature character of parent sedimentary rocks and a high preponderance of low-molecular weight n-alkanes with maximum in n-C₁₇ and n-C₁₈, usually characteristic for bacterial organic matter type.What’s more, despite n-alkanes, the coprolites contain so far unidentified series of isoalkanes and branched alkanes, most probably genetically connected with bacteria. Are the organic compounds detected related to the fossilized bacterial structures? We hope that undergoing detailed analyses will soon show more.