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Fossil bone cells (osteocytes) are known mainly from the shape-casting vacuities they leave behind after cell decay; however, they may occasionally be preserved as three-dimensionally fossilized soft parts. Here we present brownish to rust-coloured microbodies, extracted from a Middle Triassic (ca. 245 Ma) bone of the reptile Nothosaurus, which are morphologically consistent with bone cells of present-day vertebrates. In situ imaging shows that these structures, which are reminiscent of bone cells, are harboured in lacunae framed by the bone matrix. Chemical characterization using energy-dispersive X-ray, Raman, and X-ray photoelectron spectroscopy revealed the presence of various phases of iron oxide mineralization. The predominant mineral phases are hematite and goethite; magnetite and maghemite appear to occur sporadically. It is not clear how these nanograined mineral phases were formed. Most likely mineralization proceeded very early and was triggered by local microenvironmental conditions favouring the precipitation of iron phases. The absence of a distinct signal indicating organic molecules suggests that the original bone cells underwent autolysis or other degradative processes before or during mineralization. [ABSTRACT FROM AUTHOR]

Fossil biomolecules from an endogenous source were previously identified in Cretaceous to Pleistocene fossilized bones, the evidence coming from molecular analyses. These findings, however, were called into question and an alternative hypothesis of the invasion of the bone by bacterial biofilm was proposed. Herewith we report a new finding of morphologically preserved blood-vessel-like structures enclosing organic molecules preserved in iron-oxide-mineralized vessel walls from the cortical region of nothosaurid and tanystropheid (aquatic and terrestrial diapsid reptiles) bones. These findings are from the Early/Middle Triassic boundary (Upper Roetian/Lowermost Muschelkalk) strata of Upper Silesia, Poland. Multiple spectroscopic analyses (FTIR, ToF-SIMS, and XPS) of the extracted "blood vessels" showed the presence of organic compounds, including fragments of various amino acids such as hydroxyproline and hydroxylysine as well as amides, that may suggest the presence of collagen protein residues. Because these amino acids are absent from most proteins other than collagen, we infer that the proteinaceous molecules may originate from endogenous collagen. The preservation of molecular signals of proteins within the "blood vessels" was most likely made possible through the process of early diagenetic iron oxide mineralization. This discovery provides the oldest evidence of in situ preservation of complex organic molecules in vertebrate remains in a marine environment.