EXPERIMENTAL TAPHONOMY OF PROTISTS

The fossil record of protists represents a crucial record of early eukaryotic ecosystems in the Proterozoic Eon—a period of immense biotic and environmental turnover. There remain outstanding questions, however, surrounding how protists are preserved, and thus to what extent evolutionary patterns over this critical interval of the Earth’s history are accurately represented by their fossil record. Although previous work has tackled protist taphonomy through the geochemical characterization of microfossils, replicating modes of preservation under laboratory conditions (‘experimental taphonomy’) is also a powerful method for investigating fossilization pathways. Most experimental studies to date have focused on animals or bacteria. Protists, which include organisms like foraminifera, amoebae, and algae, have different biomolecular compositions and physiologies than bacteria, and are typically smaller than their animal relatives. Consequently, they are likely subject to different controls on fossilization. Of particular interest is the potential role(s) played by clay minerals. Previous work has suggested that clay minerals can play a role in preservation by either: a) creating a physical barrier which seals off the organism from the larger environment; b) templating onto labile tissues, enhancing their decay resistance, and facilitating cast formation; or c) through the effects of their anti-microbial properties on decay suppression. Here, we describe a suite of taphonomic experiments designed to test between these models and help understand the specific role(s) played by clays in the preservation of protists. We present preliminary results from a case study investigating the decay of eukaryotic algae in the presence of kaolinite and illite.