A coccoid, colony-forming cyanobacterium from the Lower Devonian Rhynie chert that resembles Eucapsis (Synechococcales) and Entophysalis (Chroococcales)

Abstract The Rhynie chert provides sublime fossils of cyanobacteria from an Early Devonian hot spring ecosystem. However, only a small fraction of the diversity has been documented. Rhyniotaxillus devonicus nov. gen. et sp., a minute coccoid cyanobacterium from the Rhynie chert, is characterized by cuboid to somewhat irregular colonies of up to 64 cells (cell diameter: 2.5–3.5 μm) arranged into sarcinoid packages, and held together by prominent gelatinous envelopes. Colony morphology parallels that seen in certain present-day species of Eucapsis (Synechococcales) and Entophysalis (Chroococcales), as well as Eoentophysalis belcherensis , a Precambrian fossil equivalent of Entophysalis . The systematic affinities of R. devonicus remain unresolved. Nevertheless, this discovery expands our knowledge of cyanobacterial diversity in early non-marine ecosystems.