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<p>Exceptional preservation of ichthyosaur fossils in the Toarcian (~183–180 Ma) Posidonia Shale of southwest Germany was previously attributed to sustained anoxia or euxinic conditions that excluded aerobic scavengers and promoted early diagenetic mineralization. Here we show a partial ichthyosaur specimen within a carbonate concretion that contained three distinct biogeochemical compartments — the host shale, concretion matrix, and fossil bones — reflecting contrasting redox conditions during decomposition and early diagenesis. Under euxinic conditions, sulfate-reducing bacteria in the sediment generated isotopically light bicarbonate, which precipitated as the&#xa0;micritic calcite of the concretion. The bones uniquely preserve highly degraded, heavy carbon-enriched organic matter and heavy sulfur-enriched barite infilling the marrow cavities. We hypothesize this barite was produced by sulfur-oxidizing bacteria that anaerobically metabolized sulfide to sulfate. These results demonstrate that coupled microbial redox processes and carbonate cementation occurred within microenvironments associated with ichthyosaur bodies that enabled their three-dimensional preservation during the Early Jurassic.</p>

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Microbial oxidation and carbonate cementation led to three-dimensional preservation of ichthyosaur bones

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年3月25日

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  • Andrew Ji Yao Jian,
  • Lorenz Schwark,
  • Stephen Francis Poropat,
  • Alex Ian Holman,
  • Luke Marshall Brosnan,
  • Maria Diaz Mateus,
  • Michael Ernst Böttcher,
  • Kliti Grice

摘要

Exceptional preservation of ichthyosaur fossils in the Toarcian (~183–180 Ma) Posidonia Shale of southwest Germany was previously attributed to sustained anoxia or euxinic conditions that excluded aerobic scavengers and promoted early diagenetic mineralization. Here we show a partial ichthyosaur specimen within a carbonate concretion that contained three distinct biogeochemical compartments — the host shale, concretion matrix, and fossil bones — reflecting contrasting redox conditions during decomposition and early diagenesis. Under euxinic conditions, sulfate-reducing bacteria in the sediment generated isotopically light bicarbonate, which precipitated as the micritic calcite of the concretion. The bones uniquely preserve highly degraded, heavy carbon-enriched organic matter and heavy sulfur-enriched barite infilling the marrow cavities. We hypothesize this barite was produced by sulfur-oxidizing bacteria that anaerobically metabolized sulfide to sulfate. These results demonstrate that coupled microbial redox processes and carbonate cementation occurred within microenvironments associated with ichthyosaur bodies that enabled their three-dimensional preservation during the Early Jurassic.