CT-SCANNING OF PHOSPHATIZED ANIMAL EMBRYOS OF THE NEOPROTEROZOIC DOUSHANTUO FORMATION: A LOOK INSIDE

Embryos in the fossil record are especially rare, as are unambiguous examples of Precambrian metazoan life. The animal embryos of the Neoproterozoic Doushantuo Formation of Weng’an, China are phosphatized, allowing for preservation of cellular and possible subcellular tissues, and may hold important clues about some of the earliest multicellular organisms. Embryos extracted from the unit were analyzed using X-radiographic microfocus computed tomography (microCT). MicroCT scanning allows for noninvasive, nondestructive internal and external study of these ~500 µm diameter samples and enables visualization of compositional differences which reflect biological and/or taphonomic features.

Subcellular structures, possibly representing nuclei or spindle poles, may exist in several of the samples. To test the hypothesis that these structures represent embryological features, their presence, shape, volume, location, and distribution within certain cells was examined. Embryos representing 4-16 cell ontogenetic stages were emphasized in this analysis.

Although the embryos represent many ontogenetic stages, from single- to many-celled varieties, it is unclear what taxonomic diversity is represented among the embryo population. To determine if these embryos represent a single taxon or multiple taxa and/or if there are distinctive characteristics of embryos as they develop, embryos of the same ontogenetic stages were studied collectively with concern for angles of cell cleavage, cell shape, cell volume, and cell distribution within the embryo. To accomplish this objective, three-dimensional isosurface models of embryos and their structures—cells, possible subcellular structures, and inorganic features—were constructed and analyzed.