Cyanobacterial macrophytes in an Early Silurian (Llandovery) continental biota: Passage Creek, lower Massanutten Sandstone, Virginia, USA

Abstract

A compression macrofossil with structure consisting of mineral‐replaced filaments embedded in an amorphous carbonaceous matrix is described as a macrophytic cyanobacterial colony from continental assemblages of the Early Silurian (Llandovery) Passage Creek biota, in the lower Massanutten Sandstone (Virginia, USA). Filaments are predominantly multiseriate and consist of spheroidal crystalline aggregates representing early pyrite (subsequently replaced by iron hydroxides) precipitated preferentially inside cells. Interpretation of the fossils as cyanobacteria is based on close similarities to modern organisms in terms of overall morphology and production of copious extracellular investments, filament and cell sizes, and continental epigeal (freshwater or terrestrial) habitat. This interpretation incorporates data on cyanobacterial taphonomy and mechanisms of diagenetic mineral precipitation. These fossils are part of the oldest macrofossil assemblages documenting well‐developed and diverse communities on continents. They provide the earliest direct evidence for cyanobacteria in strictly continental habitats, corroborating the commonly held but poorly documented view that cyanobacteria were among the initial colonizers of continents.

The earliest records of internally stratified cyanobacterial and algal lichens from the Lower Devonian of the Welsh Borderland

“…The global impact of photoautotrophic cryptogamic ground covers on CO 2 and N 2 fixation is currently being explored (Elbert et al ., ). Lichenized and nonlichenized fungi, together with free‐living cyanobacteria and algae, might have formed extensive, species‐rich terrestrial rock surface and soil crust communities before and at the advent of plants (Heckman et al ., ; Tomescu et al ., ; Retallack, ). Their abundance might be indicated by the large quantities of nonvascular plant fragments present in Silurian and Lower Devonian macerates (Edwards, , ; Wellman, ).…”

“…However, as concluded from geochemical signals, cyanobacteria seem to have colonized palaeosol surfaces in terrestrial ecosystems as early as the Archaean (2.6–2.7 billion yr ago; Watanabe et al ., ). Live or dead, cyanobacterial and algal mats (Tomescu & Rothwell, ; Tomescu et al ., ) served as a source of fixed C and, in the case of diazotrophic cyanobacteria, of fixed N to land‐dwelling fungi long before the advent of embryophytes (Retallack, ). Switches from saprophytic or parasitic to mutualistic interactions with cyanobacteria and algae occurred independently in unrelated groups of fungi, and lichenization was repeatedly lost (Lutzoni et al ., , ; Nelsen et al ., ).…”

Earliest fossil record of bacterial–cyanobacterial mat consortia: the early Silurian Passage Creek biota (440 Ma, Virginia, USA)

“…1B,C). The cyanobacterial cells were initially filled with pyrite, which was subsequently replaced by iron oxyhydroxides during fossilization (Tomescu et al ., 2006).…”

“…1A) that contains the bacterial fossils described here is one of the largest compressions discovered to date at Passage Creek: 61 mm long, 7–9 mm wide and 250–300 µm thick. A detailed description of these cyanobacterial fossils, as well as discussions of their taphonomy, mode of fossil preservation and systematic affinities, is provided in Tomescu et al . (2006).…”

“…440 million years old) Massanutten Sandstone host a rich fossil biota at Passage Creek, Virginia, USA (Pratt et al ., 1978; Tomescu & Rothwell, 2006). The Passage Creek biota has yielded a macrofossil compression described recently as a macrophytic cyanobacterial colony (Tomescu et al ., 2006). This fossil yielded the associated bacteria that we report here.…”