Stigonema (Nostocales, Cyanobacteria) in the Rhynie chert (Lower Devonian, Scotland)

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

“…Our new fossils, along with those described by Croft and George, 39 clearly document distinctive, morphologically complex Nostocales in wet soils, warm springs and/or episodically inundated soils of the time. And, as noted above, further evidence of Rhynie nostocaleans has been provided by Krings, 29 who described clearly multiseriate populations similar to those of extant Stigonema. Loron et al.…”

“…Cyanobacteria are relatively common and diverse elements of the Rhynie biota (e.g., 27 , 28 , 29 ) frequently encountered in ever wet or episodically flooded parts of the local environment. 30 Several colony-forming coccoidal taxa have been reported, 28 , 31 , 32 , 33 , 34 , 35 but filamentous cyanobacteria are more common.…”

“…Molecular phylogenies, however, show that the stigonematalean clade nestles within the Nostocales. 40 Recently Krings 29 described Rhystigonema obscurum from the Rhynie chert, a multiseriate, true-branching form, placed with confidence within the Stigonemataceae.…”

Entophysalis in the Rhynie chert (Lower Devonian, Scotland): implications for cyanobacterial evolution

“…The fact that formations as the one described in this study have not previously been reported from the Rhynie cherts, notwithstanding the intensive research that has been conducted on this Lagerstätte for more than 100 years, could suggest that entophysalids were rare constituents of the Rhynie ecosystem. It is also possible, however, that these cyanobacteria occurred only in certain areas of the ecosystem that did not become preserved in the chert, or that are not represented by the chert blocks examined to date (Krings, 2021 c ). On the other hand, larger cyanobacterial colonies and formations held together by mucilage may rapidly disaggregate into individual cells and small cell groups after burial such that no evidence of an entophysalid affinity remains (Sergeev et al 2012).…”

“…Two forms, of which one is coccoid and Gloeocapsa - and Chroococcidiopsis -like, the other filamentous, allegedly heterocystous, and suggested to belong to the Nostocales, occur as photobionts of the putative cyanolichen Winfrenatia reticulata (Taylor et al 1997; Karatygin et al 2009). A further eight forms are filamentous, including Archaeothrix oscillatoriformis and A. contexta (Kidston & Lang, 1921; Krings et al 2009; Krings, 2021 a ); Kidstoniella fritschii , Langiella scourfieldii and Rhyniella vermiformis (Croft & George, 1959; recently merged into one taxon, L. scourfieldii , by Strullu-Derrien et al 2023); Croftalania venusta (Krings et al 2007; Krings, 2021 b ); Palaeolyngbya kerpii (Krings, 2019) and the complex, Stigonema -like Rhystigonema obscurum (Krings, 2021 c ). Loron et al (2023) illustrate what may be another Stigonema -like form.…”