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

Abstract

A new cyanobacterium, Patagonifilum jurassicum nov. gen. et sp., is structurally preserved in Late Jurassic hydrothermally influenced siliceous chert from the Deseado Massif, Patagonia, Argentina. The cyanobacterium occurs in the form of loosely to densely spaced, heteropolar filaments (up to 4.5 μm wide) that form turf-like stands, or spherical to hemispherical colonies on different substrates, usually degraded plant stems. Filaments consist of barrel-shaped cells enveloped in a non-stratified sheath, and basal cells that are distinct. The fossil is similar to certain present-day members of the Oscillatoriales (e.g., Homoeothrix), Synechococcales (e.g., Tapinothrix), and Nostocales (e.g., Rivularia, Gloeotrichia). Associated with the cyanobacteria are spheroidal to ovoid vesicles, up to 45 μm in diameter, which occur singly or clustered, mostly near the base of the filaments. They resemble certain present-day zoosporic fungi, and algae, coccoid cyanobacteria, and possibly certain arthropod eggs; however, their systematic affinities remain unresolved. This discovery is nevertheless important because it suggests that the cyanobacterial overgrowths from the Patagonian Jurassic cherts were not monospecific, but rather comprised different organisms that perhaps even interacted with each other.