MORPHOLOGICAL AND GEOCHEMICAL INVESTIGATION OF GRYPANIA SPIRALIS: A NEW LOOK AT AN OLD FOSSIL

Grypania spiralis occurs as unbranched, ribbon-like coils that are preserved two-dimensionally as bedding plane compressions, carbonaceous films, or faint colorations. Although Grypania is typically considered the oldest, potentially multicellular eukaryotic alga, its taxonomic affinity remains controversial (cf. Sharma and Shukla 2009). Current understanding of Grypania is based on reflected-light microscopy that shows neither a definitive multicellular construct (e.g. individual cells), nor cell wall ultrastructure that might be interpreted as eukaryotic in origin. The importance of Grypania to our understanding of early Earth evolution requires a reinvestigation of these enigmatic fossils.

Here we present initial results of analysis of Grypania spiralis, using samples from the US (Greyson Shale, Belt Supergroup), India (Rohtas Formation, Vindhyan Basin), and China (Gaoyuzhuang Formation, Changcheng System). Although Grypania ribbons are clearly visible under reflected light, environmental scanning electron microscopy (ESEM) show only slight topographic depressions in secondary electron detector mode. When viewed in backscatter detection mode, ribbons of Grypania are indistinguishable from the surrounding shale matrix. Elemental mapping of Grypania with x-ray energy dispersive analysis (EDS) provides support for ESEM observations, with no elemental differences detected between Grypania ribbons and the shale matrix. Even where differences in coloration are visible in both reflected light and ESEM secondary detection mode, such as “annulations” in some Indian specimens, no identifiable chemical or textural differences between the material and shale matrix have been identified. Continuing analysis of newly collected Grypania samples will help distinguish whether the observed absence of detectible fossil material results from natural taphonomic processes or from the secondary oxidation of organic material.