A review of the latest findings relating big filamentous sublittoral bacteria of sediments under the oxygen minimum zone (OMZ) of the eastern Pacific, and, on the basis of associated morphological and environmental factors, an analysis and comparison of extant and Precambrian similar benthic microorganisms is performed. Based on the similarity between the two communities and the fact that certain features presented by extant bacterial mats may explain a special type of Precambrian stromatolites, i.e., the microbialites, we suggest that both extant big filamentous bacteria and their mats may represent analogs of those existing in Precambrian oceans providing opportunities for research and clues on the evolution of early life in the ocean's shelf sediments and that this `forgotten biosphere' will eventually contribute to a better understanding of the biodiversity of present day's microbial world.