Possible eucaryotic algae (Bangiophycidae) among early Proterozoic microfossils
Recent data concerning extant planktonic red algae, chrysophytes, and haptophytes suggest possible reallocation of certain previously described middle and late Precambrian microfossils to one or more of these eucaryotic groups. Both binary fission and budding reproductive methods characterize Huroniospora of the Gunflint Iron Formation and Palaeocryptidium of the Bohemian Proterozoic. Their reproduction, morphology, habitat, and wide geographic distribution, as well as phylogenetic interpretations based on morphology, life cycles, and biochemistry of extant algae, suggest possible assignment of the Precambrian fossils to the unicellular red algal Order Porphyridiales (Subclass Bangiophycidae) rather than to the procaryotic blue-green algae or to the terrestrial fungi as recently suggested. Living Porphyridium may show peripheral multiple budding, with the resultant small cells held in the mucilaginous sheath that surrounds the parent cell, suggesting a similar relationship of Eosphaera tyleri Barghoorn and the Type 4 organism of Hofmann and Jackson. Eucapsis ? from the Paradise Creek Formation also might be referable to the Rhodophyta (spore packets of Bangiales) or Chromophyta (colony stage of Haptophyceae or Chrysophyceae) rather than to the blue-green algae. Reassignment of the Gunflint taxa to the red algal Subclass Bangiophycidae would make this the earliest fossil record of this group; preservation of these unicellular organisms is due to the exceptional nature of the enclosing chert. The suggested reassignment also would date the evolution of the eucaryotic cell and of vegetative mitotic cell division by binary fission and budding by at least 1.9 × 10 9 yr B.P., about the time previously hypothesized as representing the final transition from an anoxic to an oxygenic atmosphere. Genetic recombination resulting from sexual reproduction, with nuclear fusion and meiosis, first appeared in red or green algae at some time within the succeeding 1 b.y.