Filamentous cyanobacteria and associated microorganisms structurally preserved in a Late Jurassic chert from Patagonia, Argentina (2023)


Cyanobacteria are oxygenated photoautotrophic prokaryotes that have been instrumental as primary producers in the dynamics of biogeochemical cycling in Earth's ecosystems over time (Tomitani et al., 2006; Schirrmeister et al., 2011; Whitton and Potts, 2012). Its evolution is associated with the oxygenation of the primitive atmosphere and therefore with the global transformation of ecosystems and the evolution and diversification of oxygen-based life (Schirrmeister et al., 2013; Lyons et al., 2014). Cyanobacteria are mostly unicellular, but can also occur as filaments, clumps, or colonies; They present a great diversity of forms, as well as cellular and colony differentiation (Castenholz, 2001). Many cyanobacteria represent important food sources in aquatic ecosystems (Adams et al., 2012); others enter into various types of relationships with plants, animals, fungi, and other protists (eg, Rai et al., 2002; Thompson et al., 2012).

With this recognition of the ecological importance of cyanobacteria, detailed documentation of their evolutionary history, including the roles they played in past biological and ecological processes, is important for understanding the complexity and evolution of ancient and modern ecosystems ( e.g., Krings, 2019; Krings and Sergeev, 2019). Cyanobacteria may have originated long before 3.0Ga, as evidenced by an extensive fossil record (Sergeev et al., 2012), molecular data (eg, Schirrmeister et al., 2013), and conserved trends in oxygen levels. free (eg, Sánchez-Baracaldo 2015; Schirrmeister et al., 2015). Many cyanobacterial fossils have been described throughout the geologic column and directly compared to present forms (eg, Golubic and Lee, 1999; Schopf, 2012). However, most of these fossils come from the Proterozoic and are of marine origin.

Documented evidence of cyanobacteria from non-marine Mesozoic environments is rare (for example, Beraldi-Campesi et al., 2004; Harper et al., 2020) and thus adds to our knowledge of the roles these organisms played. in non-marine aquatic environments. Mesozoic and excessively incomplete terrestrial paleoecosystems. Therefore, expanding the record through the discovery of new nonmarine rock deposits that contain fossil cyanobacteria, along with the identification of new species from deposits known to produce fossil cyanobacteria, is a key step toward a more accurate assessment of cyanobacteria. in ancient ecosystems.

This paper presents in situ stands ofJurassic of Patagonianov. gene. et sp., a heteropolar filamentous cyanobacterium from siliceous cherts from the Middle-Upper Jurassic of the Deseado Massif in Santa Cruz, Argentina. The shape represents the world's first evidence of structurally conserved non-marine cyanobacteria from the Jurassic. Furthermore, many of the cyanobacterial stands harbor various types of vesicles of unknown affinity that are usually found singly or clustered near the base of the filaments, suggesting thatP. jurassicumThe La Bajada flints were closely associated with, and perhaps even interacted with, other organisms.

section excerpts

geology and age

The Deseado Massif geological province was formed by an extensive volcanic event that formed part of the Chon Aike Large Silicon Igneous Province (Patagonia to Antarctica; Pankhurst et al., 1998), and is related to the fragmentation of Gondwana during the opening of the Proto-Atlantic Ocean in the Middle-Late Jurassic (177.8–150.6 Ma) (Pankhurst et al., 2000; Riley et al., 2001; Ramos, 2002). The volcanic and volcaniclastic rocks of the Maciço do Deseado are grouped in the Bahía Laura Complex, which


cyanobacteria––The material in question consists of more than a dozen in situ cyanobacterial scaffolds, each comprising a large number of loosely to densely spaced, structurally and three-dimensionally conserved heteropolar filaments (up to ~300 filaments/mm of diameter). thin section), arranged in irregular, carpet- or grass-like formations (Plate 1, Figs. 3 and 4) or spherical to hemispherical colonies (up to 1 mm in diameter). Groups of cyanobacteria occur in a variety of degraded parts of the plant (roots, stems, pollen

cyanobacteriauncertain seat

Gender PatagonianGarcia Massini, Guido, Campbell, Sagasti, Krings nov. gen.

Affinities of the described cyanobacteria

Jurassic of PatagoniaIt is characterized by uniseriate heteropolar filaments of serially aligned cells enclosed in a translucent sheath. This combination of basic structural features makes the fossil comparable to several extant filamentous cyanobacteria in Oscillatoriales and Nostocales (Rippka et al., 1979; Castenholz, 2001). There are high levels of morphological congruence betweenP. jurassicumand current members of the genusHomeotrix, which are characterized by being uniseriad,

concluding remarks

Jurassic of Patagoniait is one of the few structurally conserved cyanobacteria that have been documented in detail and formally described in non-marine Mesozoic paleoecosystems. Their discovery contributes to the understanding of the complexity and dynamics of the biotic communities of the Jurassic Patagonian thermal ecosystems in particular, and of the Mesozoic terrestrial ecosystems in general.Jurassic of PatagoniaIt is similar in basic morphology to certain extant members of the

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Declaration of competing interests

The authors declare that they have no competing financial interests or known personal relationships that could influence the work reported in this article.

expressions of gratitude

We thank the Department of Culture of the Province of Santa Cruz for supporting our Research and granting research permits to study geothermal deposits in the Maciço do Deseado. We also thank Patagonia Gold inc. to facilitate field work. Funding for this project came from theNational Council for Scientific and Technical Research(CONICET, Pages 202 and 173 to the JLGM), theMinistry of Science, Technology and Productive Innovation(MINCyT, PICT 2104–3496 for JLGM & DG) and National Geographic Society (para.

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