FOSSIL BACTERIA FROM THE GREEN RIVER FORMATION

The excellent preservation of fossils in the sediments of the Eocene Green River Formation of Colorado, Wyoming, and Utah has been well documented for a hundred-fifty years. This remarkable series of finely-laminated fluvio-playa-lacustrine sediments have produced some of the world=s most spectacular vertebrate, invertebrate, and plant fossils. Investigation of sediments from the Green River Formation in the Green River Basin of Wyoming using scanning electron microscopy (SEM) revealed remarkably preserved fossil bacteria. These bacteria occur as mineral replacement pseudomorphs and clay-coated casts. The fossil prokaryotes can be separated into distinct morphotypes: ball-shaped, rod-shaped, and filamentous. Positive identification of fossilized bacteria is not possible because either: (1) the internal structure of the individual bacterium has been completely replaced by minerals, leaving only a pseudomorphic replica or, (2) the bacterium has become encrusted with clay minerals rendering the internal structure inaccessible. However, morphological comparisons can be made to modern bacteria with the conclusion that the fossil bacteria represent examples from the cyanobacteria, sulfate-reducing bacteria, and bacterial decomposer families.