Experimental mineralization of crustacean eggs: new implications for the fossilization of Precambrian–Cambrian embryos

[摘要] Phosphatized globular microfossils from the Ediacaran and lower Cambrian ofSouth China represent an impressive record of early animal evolution anddevelopment. However, their phylogenetic affinity is strongly debated.Understanding key processes and conditions that cause exceptional egg andembryo preservation and fossilization are crucial for a reliableinterpretation of their phylogenetic position. We conducted phosphatizationexperiments on eggs of the marbled crayfish Procambarus that indicate a close linkbetween early mineralization and rapid anaerobic decay of the endochorionalenvelope. Our experiments replicated the different preservational stages ofdegradation observed in the fossil record. Stabilization of the sphericalmorphology was achieved by pre-heating of the eggs. Complete surfacemineralization occurred under reduced conditions within one to two weeks,with fine-grained brushite (CaHPO₄ · 2H₂O) and calcite. Themechanisms of decay, preservation of surface structures, and mineralreplacement in the experiment were likely similar during fossilization ofCambrian embryos.

[学科分类] 地球化学与岩石