Treatise on Invertebrate Paleontology, Part B: Prokaryota (Bacteria and Archaea)

About this book

From the introduction:

"In 2012, we began discussing the problems associated with prokaryote fossil systematics in palaeontology and whether this subject belonged in the Treatise on Invertebrate Paleontology. With Precambrian palaeontology gaining increasing traction in novel analytical studies, we agreed it would be timely for the Treatise to publish a volume dedicated to prokaryotes. One of the problems we encountered was how to categorize prokaryotes and fit this organismic group into the traditional systematic framework of the Treatise. In the prokaryote world, speciation in the Darwinian sense does not exist, and, more so, prokaryotes commonly assemble into highly complex communities called biofilms. Microbial cells are rarely preserved, and sedimentary structures arising from prokaryote activity constitute biofilm expressions. Biofilms, however, are complex assemblages of microorganisms and a dominant group cannot always be of geological significance in the sense of causing a visible fossil, texture, or structure. For these reasons, it seemed prudent to explore the topic of Prokaryota in the fossil record by presenting a volume that would include a general overview on the main fossil types that constitute this indisputably largest group of organisms on Earth. Future work may contribute to categorizing taphonomic groups and testing biostratigraphic application, which may well result in additional volumes on Prokaryota.

This volume begins with an introduction into biofilms that have mostly been the subject of medical research before moving into the limelight of geosciences. Biofilms are assemblages of microbes that organize into a three-dimensional structure with the single cells attached to a substrate by their extracellular polymeric substances (EPS) – in colloquial terms also called slime. Traditional sedimentology and palaeontology are not familiar with biofilms but are definitively familiar with microbial mats (algal mats) that are basically large-scale biofilms occurring in aquatic settings. Such mats are well known as producers of microbialites, of which the carbonate buildups (stromatolites) in shallow coastal zones are prominent examples. Such buildups form through the metabolic activity of the biofilm/mat community in which each member is interacting with the next, as well as with environmental parameters. Biofilms and mats also contributed to the enormous quantities of Banded Iron Formations (BIFs), to date the most important ore deposits in the world. Where mats develop in clastic settings of little to no mineral precipitation, microbially induced sedimentary structures (MISS) represent the microbialite spectrum. Microbial mats, microbialites, and BIFs constitute large structures, but they may include myriads of microfossils of the ancient structure-formers. However, the palaeontological spectrum of prokaryotes also includes deposits of fossils of cells and filaments preserved in situ as carbonaceous matter in rapidly precipitated mineralogies, such as glass-like chert. In some examples, the organic matter had been replaced by minerals such as pyrite.

Prokaryote fossils and structures have modern counterparts that can be studied. Typically, the record spans from the early Archean (perhaps Hadean) to the modern. Indeed, the modern serves as the key to the past and is instrumental for the exploration of Earth history, especially that of the Precambrian."

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