A colony-forming microorganism with probable affinities to the Chroococcales (cyanobacteria) from the Lower Devonian Rhynie chert

The Rhynie chert has provided a wealth of information on Early Devonian non-marine aquatic and terrestrial life. However, our understanding of the microbial biodiversity in this hot spring paleoecosystem remains incomplete. In this paper we describe Rhyniosarcina devonica nov. gen. et sp., a microorganism from the Rhynie chert that forms cubical, spheroidal, or irregular colonies of up to several hundred densely packed cells (< 2.5-5.5 μm in diameter). Square groups of four cells and sarcinoid packages of eight cells represent the basic modular units in the construction of the colonies. Cell division is by binary fission in three planes in space; new colonies form by colony dissociation. Rhyniosarcina devonica is interpreted as a cyanobacterium with affinities to the Chroococcales based on morphological similarities to extant colony-forming chroococcalean cyanobacteria, especially members in the genus Cyanosarcina. This discovery expands our knowledge of the diversity of primary producers in the Rhynie chert.