Hapalosiphonacean cyanobacteria (Nostocales) thrived amid emerging embryophytes in an early Devonian (407-million-year-old) landscape

Cyanobacteria have a long evolutionary history, well documented in marine rocks. They are also abundant and diverse in terrestrial environments; however, although phylogenies suggest that the group colonized land early in its history, paleontological documentation of this remains limited. The Rhynie chert (407 Ma), our best preserved record of early terrestrial ecosystems, provides an opportunity to illuminate aspects of cyanobacterial diversity and ecology as plants began to radiate across the land surface. We used light microscopy and super-resolution confocal laser scanning microscopy to study a new population of Rhynie cyanobacteria; we also reinvestigated previously described specimens that resemble the new fossils. Our study demonstrates that all are part of a single fossil species belonging to the Hapalosiphonaceae (Nostocales). Along with other Rhynie microfossils, these remains show that the accommodation of morphologically complex cyanobacteria to terrestrial ecosystems transformed by embryophytes was well underway more than 400 million years ago.

Automated summary

Cyanobacteria have a long evolutionary history and are abundant in marine rocks and terrestrial environments. The Rhynie chert provides a well-preserved record of early terrestrial ecosystems, allowing us to study the diversity and ecology of cyanobacteria as plants began to colonize the land. Through microscopy techniques, we discovered a new population of Rhynie cyanobacteria and confirmed that they belong to the Hapalosiphonaceae family. This study demonstrates that complex cyanobacteria had already adapted to terrestrial ecosystems transformed by plants over 400 million years ago.