Proterozoic Fossil Cyanobacteria
Authors: Sergeev V. N. , Sharma Mukund , Shukla Yogmaya 
Published: September 2022

A monographic account is presented on the fossil Proterozoic cyanobacteria. It chronicles the 60 years of history of investigations on the Precambrian microfossils. The researches on Precambrian microfossils have revealed a new, earlier unknown, world of oldest microorganisms and divulged the steps in life’s evolution on the earth. Documented records show that cyanobacteria occupied all available ecological niches of the Precambrian biosphere and filamentous and coccoidal cyanobacteria were the dominant microbial community. Extinct fossilized cyanobacteria in diagenetic cherts of the Precambrian are comparable in morphology and behavior with extant forms. These oxygenic phototrophic microorganisms were masters for at least first 3.0-3.5 billion years of the Earth history and almost did not change for billion years. The unprecedented evolutionary conservatism of the cyanobacteria is established so much so that modern systematics of cyanobacteria can be applied on Proterozoic forms at least, up to the family level. More than half a century of research on Precambrian microfossils demands refinement in taxonomy and allows differentiation between products of taphonomy and primarily biological features of fossilized cyanobacteria as well as those features formed as a result of postmortem degradation and subsequent diagenetic alternations. The paper embodies all cyanobacterial taxa broadly accepted by most of the researchers and provides complete revision of all Precambrian fossil cyanobacterial remains. It presents a comprehensive information on the taxonomy of cyanobacterial and related microorganisms along with emendations with due considerations of possible processes of post-mortem alterations. Detailed analysis of fossil cyanobacteria populations has revealed 50 genera and 92 species as truly acceptable forms. Of this, more than 10 genera and 18 species are recognized as problematic cyanobacterial taxa that could be alternatively interpreted as Protista. The present review contains diagnosis and descriptions of genera as well as type and some other very important species. The information on other species (size, type specimen, distribution) is given in the table format along with the described genera. All valid taxa described from the Proterozoic microbiotas are incorporated in this work. Problematic remains of Archaean (?) cyanobacteria are not included because of their uncertain and disputable biogenic origin. The relevant data of molecular biology and other methods applied in systematics of modern cyanobacteria are discussed in the paper. Besides, main taxonomic part and relevant discussion on the morphology of microfossils the palaeobiology, palaeoecology and geological history of cyanobacteria are also provided. The present paper contains following taxa: Family- CHROOCOCCACEAE: Brachypleganon, Coniunctiophycus, Corymbococcus, Eoaphanocapsa, Eogloeocapsa, Eosynechococcus, Gloeodiniopsis, Gloeotheceopsis, Gyalosphaera, Sphaerophycus, Tetraphycus; Family- ENTOPHYSALIDACEAE: Coccostratus, Eoentophysalis; Family- DERMOCARPACEAE: Polybessurus; Family- HYELLACEAE: Eohyella; Family- PLEUROCAPSACEAE: Palaeopleurocapsa, Scissilisphaera; Family- XENOCOCCACEAE: Synodophycus; Family- OSCILLATORIACEAE: Calyptothrix, Cephalophytarion, Cyanonema, Eomicrocoleus, Eoschizothrix, Filiconstrictosus, Heliconema, Obruchevella, Oscillatoriopsis, Palaeolyngbya, Partitiofilum, Siphonophycus, Uluksanella; Family- NOSTOCACEAE: Eosphaeronostoc, Veteronostocale; Family- SCYTONEMATACEAE: Circumvaginalis, Ramivaginalis; Order- NOSTOCALES OR STIGONEMATALES: Archaeoellipsoides, Orculiphycus, INSERTAE SEDIS: Animikiea, Chlorogloeaopsis, Chuaria, Clonophycus, Glenobotrydion, Gunflintia, Huroniospora, Leiosphaeridia, Leptoteichos, Myxococcoides, Phanerosphaerops, Polysphaeroides, Polytrichoides.