Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago

Abstract

The evidence for macroscopic life during the Palaeoproterozoic era (2.5-1.6 Gyr ago) is controversial. Except for the nearly 2-Gyr-old coil-shaped fossil Grypania spiralis, which may have been eukaryotic, evidence for morphological and taxonomic biodiversification of macroorganisms only occurs towards the beginning of the Mesoproterozoic era (1.6-1.0 Gyr). Here we report the discovery of centimetre-sized structures from the 2.1-Gyr-old black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, which we interpret as highly organized and spatially discrete populations of colonial organisms. The structures are up to 12 cm in size and have characteristic shapes, with a simple but distinct ground pattern of flexible sheets and, usually, a permeating radial fabric. Geochemical analyses suggest that the sediments were deposited under an oxygenated water column. Carbon and sulphur isotopic data indicate that the structures were distinct biogenic objects, fossilized by pyritization early in the formation of the rock. The growth patterns deduced from the fossil morphologies suggest that the organisms showed cell-to-cell signalling and coordinated responses, as is commonly associated with multicellular organization. The Gabon fossils, occurring after the 2.45-2.32-Gyr increase in atmospheric oxygen concentration, may be seen as ancient representatives of multicellular life, which expanded so rapidly 1.5 Gyr later, in the Cambrian explosion.

Oxygen dynamics in the aftermath of the Great Oxidation of Earth’s atmosphere

“…As regression continued, oxic conditions are revealed again in shallow sediments depositing in the boundary between the FB2 and FC units. Consistent with this evidence for oxygenated conditions, softbodied macroscopic fossils are found in the FB2b subunit (28), and stromatolites are found in dolomites and chert of the FC unit. We lack Fe speciation for the middle part of the FC, but we note enrichments in Mo, V, and U at a single depth in the middle of this unit ( Figs.…”

“…These sandstones are sharply overlain by finely laminated black shales interbedded with thin siltstone layers deposited by waning storm surge (FB2b). It is from here that large colonial organisms have previously been reported (28). Stromatolites are found in topographic highs at the base of the FC formation (29), after which the overlying black shales of the FD formation were deposited in a transgressive phase.…”

Morphological optimization for access to dual oxidants in biofilms

“…Bacterial biofilms may exhibit complex spatial patterning at scales comparable to those of putative microbial fossils (25,47). Our biofilm system has allowed us to test the effects of different atmospheric oxygen concentrations directly and to demonstrate that the width of features changes predictably.…”

“…This raises questions such as (i) how are morphology, metabolism, and environmental conditions interconnected and (ii) how do these relationships govern the fundamental benefits and tradeoffs of multicellularity? Understanding these connections may help us understand the general trajectory by which simple and complex multicellular life evolved and allow us to better identify and quantify morphologically complex structures that may represent paleobiological populations (25).…”

Neoproterozoic substrate condition vis-à-vis microbial mat structure and its implications: Sonia Sandstone, Rajasthan, India

“…760 Ma age (Brain et al, 2012) and, although controversial, structures interpreted as colonial multi-cellular organisms from Gabon are dated at ca. 2.1 Ga (Albani et al, 2010). Many published accounts of biotic evidence of presumptive traces of soft bodied organisms from this period have been reinterpreted and reconsidered as microbial mat colonies, microbial mat remnants (cf.…”