Morphological and ecological complexity in early eukaryotic ecosystems

Abstract

Molecular phylogeny and biogeochemistry indicate that eukaryotes differentiated early in Earth history. Sequence comparisons of small-subunit ribosomal RNA genes suggest a deep evolutionary divergence of Eukarya and Archaea; C27-C29 steranes (derived from sterols synthesized by eukaryotes) and strong depletion of 13C (a biogeochemical signature of methanogenic Archaea) in 2,700 Myr old kerogens independently place a minimum age on this split. Steranes, large spheroidal microfossils, and rare macrofossils of possible eukaryotic origin occur in Palaeoproterozoic rocks. Until now, however, evidence for morphological and taxonomic diversification within the domain has generally been restricted to very late Mesoproterozoic and Neoproterozoic successions. Here we show that the cytoskeletal and ecological prerequisites for eukaryotic diversification were already established in eukaryotic microorganisms fossilized nearly 1,500 Myr ago in shales of the early Mesoproterozoic Roper Group in northern Australia.

Paleoproterozoic sterol biosynthesis and the rise of oxygen

“…Yet the majority of Paleoproterozoic and Mesoproterozoic sedimentary rocks described that are known to preserve biomarkers appear to be devoid of eukaryotic steranes, but do contain C 27 -C 35 hopane hydrocarbons of bacterial origin (Blumenberg et al, 2012;Brocks et al, 2005;Flannery and George, 2014;Luo et al, 2015). From a micro-and macrofossil perspective, ample evidence exists for the presence of unambiguously eukaryotic fossil assemblages in the Mesoproterozoic (Butterfield, 2000;Javaux et al, 2001;Javaux et al, 2004;Knoll et al, 2006;Zhu et al, 2016). Accordingly, the failure to detect a concomitant record of eukaryotic steranes suggests that their membrane lipids contained limited amounts of steroids.…”

Affinity, life cycle, and intracellular complexity of organic-walled microfossils from the Mesoproterozoic of Shanxi, China

“…The advanced level of organization of a eukaryotic cell with endomembrane system, ER and the GA, cytoskeleton, organelles including mitochondrion, plastid and machinery for sexual reproduction is inferred for these microfossils. The organelles thought to be present in early eukaryotes, primarily nucleus and mitochondrion, and structures providing the minimum requirement for eukaryotic cell functioning, i.e., endomembrane system and cytoskeleton (Stanier, 1970;Lang et al, 1999;Cavalier-Smith, 2003Dacks and Field, 2004;) have been inferred to exist in some Mesoproterozoic taxa, such as Tappania, Valeria, and Shuiyousphaeridium (Javaux et al, 2001(Javaux et al, , 2003(Javaux et al, , 2004.…”

Silicified microbiota from the Paleoproterozoic Dahongyu Formation, Tianjin, China

“…Formation from Siberia, the 1450 Ma Roper Group from Australia, the >1400 Ma Ruyang Group from North China, and the 1400 Ma Greyson Formation from United States (Xiao et al, 1997;Javaux et al, 2001;Javaux and Marshal, 2006;Peng et al, 2009;Vorob'eva et al, 2015;Adam et al, 2016). These strata (the Kotuikan Formation from Siberia is an exception) are comparable with each other for bearing the same microfossils.…”

“…Although, tens of thousands of microfossils have been reported from the Proterozoic Yanshan Basin (Sun, 2006;Shi et al, 2014), microfossils with complex morphology or ornament are still rare or debatable. Complex eukaryotes, such as Tappania, Satka and Shuiyousphaeridium, which are abundant microfossils in several locations (Xiao et al, 1997;Javaux et al, 2001;Javaux and Marshal, 2006;Peng et al, 2009;Vorob'eva et al, 2015;Adam et al, 2016), were absent in the Dahongyu Formation and any strata in the entire Yanshan Basin. Even Valeria lophostriata, which emerged in the underlying Changcheng Group, is absent in the subsequent strata.…”