Phosphatized globular microfossils from the Ediacaran and Lower Cambrian of South China represent an impressive record of early animal evolution and development, however their affinity based on putative embryonic metazoan, bacterial and inorganic features is strongly debated. Understanding key processes and conditions that cause exceptional egg and embryo preservation and fossilization are therefore crucial for a reliable interpretation of their phylogenetic position. Taphonomic experiments on eggs of the marbled crayfish indicate a close link between early mineralization and rapid anaerobic decay of the endochorional envelope, producing different preservational stages of degradation resembling the various decay stages observed in the fossil record. Stabilization of the spherical morphology was achieved by pre-heating of the eggs. Complete surface mineralization occurred under reduced conditions within one to two weeks, with fine-grained brushite (CaHPO4·2H2O) over calcite as the dominating mineral phase. Although the endochorional envelope was not preserved, experiments resulted in exceptional preservation of the embryonic tissue at the cellular level. Thus our findings suggest that the mechanisms of decay, preservation of surface structures, and mineral replacement in the experiment and during fossilization of Cambrian embryos were likely operating at a similar rationale.
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