oa Fossilisation of Fish Soft Tissue in Oxidative Microniches of Anoxic Sediments

Organic preservation in fossilization is rare, but when identified can provide insights into past ecology and evolution. This geochemical study examines an exceptional Diplomystus dentatus fish specimen (∼52 Ma) with intact soft tissue (exclusively skin), preserved through phosphate mineralization. Several fossil parts (skin, eye, bones) and matrix samples were separately analyzed. The skin exhibited elevated oxygen levels, likely resulting from fatty acid breakdown of the dermis, which supported a unique microenvironment inclusive of lipid-consuming aerobes. The seemingly paradoxical preservation of organic tissue exclusively in the oxygen-rich microniche of the fossil skin is attributed to the concomitant release of H+ ions from the dermis, with the increase in acidity supporting phosphatization and permineralization of residual skin in an otherwise carbonate-dominant system.