Transvaal Stromatolite: First Evidence for the Diversification of Cells about 2.2 x 109 Years Ago.

The well-preserved fossil remnants of filamentous blue-green algae have been found in petrographic thin sections of a dolomitic limestone stromatolite in the Transvaal Sequence of South Africa. Some of these filaments contain enlarged cells which are interpreted as akinetes. A new species and genus, Petraphera vivescenticula, is proposed for this microfossil, which is morphologically similar to the living cyanophyte genus Raphidiopsis. This would constitute the first known occurrence of cell diversification in the Precambrian with an age of about 2.2 x 10(9) years.