INVESTIGATING THE TAPHONOMY OF MICROBES BY LIGHT AND ELECTRON MICROSCOPY

Acritarchs and other microbial fossils comprise the most important body fossils of the Precambrian, and yet our tools for deciphering their phylogenetic relationships are relatively limited. The simple morphology of many microfossils results in ambiguous classification. In some cases, ultrastructure, visible by electron microscopy has proved useful in establishing taxonomic affinity. Ultrastructural interpretations are complicated by a dearth of knowledge regarding the effects of taphonomy on morphological preservation of diverse microfossils. This study represents an initial attempt to relate early post-mortem decomposition processes to the morphological and ultrastructural changes they might produce in microfossils. We seek comparable morphologies in modern and fossil microbes in order to better describe how microbes enter the fossil record.

Cultures of photosynthetic prokaryotes (cyanobacteria) and eukaryotes (algae) were incubated in the dark with natural mixed cultures of heterotrophs. Decomposition progress was evaluated at regular intervals by light and electron microscopy to assess post-mortem morphological change. Cell morphology was semi-quantitatively assessed and plotted on a ternary diagram. Similarly, scanning electron microscopy and scanning transmission electron microscopy were used to evaluate cell wall ultrastructure changes, with limited success. In addition, Neoproterozoic acritarchs were evaluated by light and electron microscopy to assess potential taphonomic characters in preserved microfossils. Although no definitive taphonomic features have been identified, several ultrastructural features of these acritarchs show promise as persistently recognizable by electron microscopy.