EXPLORING ALGAL MORPHOLOGY DURING EARLY DECOMPOSITION: TESTING HYPOTHESES REGARDING THE PROTEROZOIC FOSSIL RECORD

The early fossil record consists entirely of microbial fossils, the first of which were unicellular and filamentous bacteria. During the Proterozoic, the record additionally contains single-celled plankton (acritarchs), dominantly preserved in shales, and a few macroscopic remains. Several features suggest that acritarchs are eukaryotes. Acritarchs are morphologically diverse, usually large in size, and some have ornamentation such as spines or bumps. However, the relatively simple morphology of these fossils makes them difficult to identify reliably and, particularly, to connect these remains to extant taxonomic groups.

It has been further suggested that post-mortem features such as rolling, folding and wrinkling of cell walls may also indicate eukaryotic affinities. Observations of Proterozoic acritarchs suggest that the two basic shapes observed were formed by a process of rolling after the cell wall has been broken or peeled away. In larger fossils such as Grypania, coiled filaments occur in conjunction with organic films containing a variety of morphologies, and the connections among these mesoscopic to macroscopic features are unknown. Taphonomic alteration may be partly responsible for creating observed morphotypes, confounding the identification of original taxonomy. These hypotheses are potentially testable by conducting experiments to evaluate the effects of simple types of post-mortem change in modern algae.

In this project, we identify morphological features that are preserved or created during early stages of post-mortem alteration of modern megascopic algae. Specifically, this project examines decomposition by microbes and abrasion/disarticulation by water currents. In making these observations, we will identify specific processes that might have produced features such as folding, rolling, disarticulation, or ultrastructural alteration and compare these features to those preserved in Proterozoic organic remains.