oa Role of Sulfur Oxidising Bacteria in 3D Preservation of a Pterosaur Bone (Romualdo Formation, Santana Group, Brazil)

This study examines the diagenetic processes responsible for the remarkable 3D preservation of a pterosaur phalanx bone from the Early Cretaceous Romualdo Formation. Key factors include microbial activity, particularly sulfur-oxidizing bacteria (SOB), and chemical transformations such as phosphatisation. The bone, encased in a calcium carbonate concretion, shows lower hydrogen and higher oxygen index values compared to surrounding materials, suggesting microbial degradation. Barite and celestite minerals found in the bone support sulfur oxidation by SOB. The bone and surrounding ostracods underwent phosphatisation and contained higher sulfur content than the matrix. The presence of pyrite points to sulfate-reducing bacteria in localized areas. Rapid precipitation of fine-grained braded calcite formed a rind around the bone, while dolomite developed a halo on the side near the original bone cavity. Iron oxides found on muscle fibers indicate hemoglobin breakdown. Carbon and steroid analyses show that the bone’s C27 steroids, including cholestane, suggest a diet high in squid and fish. This is the first report of steroids in a phalanx bone. Additionally, electron microscopy revealed apatite nodules on collagen fibers, providing structural support for the pterosaur. The study uses a 3D video to illustrate these processes, enhancing our understanding of fossilization and preservation of organic matter.