Biological and taphonomic implications of Ediacaran fossil embryos undergoing cytokinesis

A collective of three-dimensionally (3D) phosphatized animal embryos with elongated olive shapes was discovered from the fossiliferous Ediacaran Doushantuo Formation (635–551 Myr) in Weng'an, Guizhou, southwest China. In order to reconstruct 3D architectures of the specimens without destroying them, a non-destructive imaging technique termed propagation phase contrast synchrotron X-ray microtomography (PPC-SR-μCT) was applied in concert with scanning electron microscopy (SEM). The results show that the embryos were enclosed in a thin capsule with an ornament of cell-like polygons on the surface. Moreover, each elongated specimen consists of two blastomeres inside the sculptured capsule, and the geometric relationship of the two blastomeres in each specimen suggests that these specimens probably represent cleaving embryos during different phases of cytokinesis. This is the first detailed description of Doushantuo fossil embryos undergoing cytokinesis, and this new discovery supports the view that not all of the ornamented Doushantuo embryos are at diapause stage. Additionally, the rare phenomenon that the dynamic cytokinesis process was captured and fixed in fossils yields valuable insights into the taphonomic process of animal embryos before early diagenesis.

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► We discovered 3D preserved Ediacaran embryo fossils undergoing cytokinesis.
► The fossil embryos undergoing cytokinesis suggest that they are normally developing embryos but not diapause ones.
► A general mode of the taphonomy process of these embryos is presented.
► Three groups of embryo fossils with different preservation qualities are distinguished.