Biodiversity of living, non marine, thrombolites of Lake Clifton, Western Australia

<p>Lake Clifton in Western Australia is recognized as a critically endangered ecosystem and the only thrombolite reef in the southern hemisphere. There have been concerns that increases in salinity and nutrient run-off have significantly impacted upon the thrombolite microbial community. Here we used cultivation-independent molecular approaches to characterize the microbial diversity of the thrombolites at Lake Clifton. The most dominant phyla currently represented are the Proteobacteria with significant populations of Bacteroidetes and Firmicutes. Cyanobacteria, previously invoked as the main drivers of thrombolite growth, represent only a small fraction (∼1–3% relative abundance) of the microbial community. We report an increase in salinity and nitrogen levels at Lake Clifton that may be contributing to a change in dominant microbial populations. This heightens concerns about the long-term health of the Lake Clifton thrombolites; future work is needed to determine if phyla now dominating this system are capable of the required mineral precipitation for continued thrombolite growth.</p

Detecting ancient life: Investigating the nature and origin of possible stromatolites and associated calcite from a one billion year old lake

Putative stromatolites and associated carbonate minerals in 1.1 Ga Stoer Group lacustrine sedimentary rocks were analysed to deduce their likely origins. Potential stromatolite examples included finely laminated and sometimes wrinkled carbonate-siliciclastic rocks of the Clachtoll Formation at Clachtoll and Bay of Stoer, and laminated limestone domes of the Poll a’Mhuilt Member (Bay of Stoer Formation) from Enard Bay. Petrography shows that the lamination and wrinkling of Clachtoll Formation specimens can most logically be explained by abiotic siliclastic sedimentary processes, namely rippling and soft-sediment deformation probably related to de-watering. Electron backscatter diffraction shows that the carbonate in these laminated Clachtoll Formation specimens was calcite, and petrography combined with clumped isotope palaeothermometry indicates it was likely to be part syn-depositional and part burial diagenetic in origin. The laminated domes of the Poll a’Mhuilt Member are shown to comprise clasts of limestone interlayered with clay, quartz, Na-rich feldspars and micas. Cathodoluminescence revealed the limestone clasts to be composite and built of sub-grains that must have been derived from an earlier, potentially Palaeoproterozoic, carbonate unit. Support for this hypothesis comes from clumped isotope palaeotemperature measurements that indicate the limestone clasts were precipitated or recrystallized under higher temperature conditions than the burial diagenetic calcite found in the Clachtoll Formation. Raman spectra of an organic carbon particle within a laminated dome of the Poll a’Mhuilt Member at Enard Bay are consistent with the organic carbon having been re-worked from the ∼2 Ga Loch Maree Group, and we speculate that this might also be true of the calcite. Microbial fossils are well known from elsewhere in the Stoer Group, but no conclusive examples were found within the thin-sections examined herein. No conclusive evidence was found to suggest that any of the examined putative stromatolites were biogenic, leading to the conclusion that they are best considered stromatolite-like sedimentary rocks (pseudostromatolites)

Enhanced cellular preservation by clay minerals in 1 billion-year-old lakes

The article of record as published may be located at http://dx.doi.org/10.1038/srep05841Organic-walled microfossils provide the best insights into the composition and evolution of the biosphere through the first 80 percent of Earth history. The mechanism of microfossil preservation affects the quality of biological information retained and informs understanding of early Earth palaeo-environments. We here show that 1 billion-year-old microfossils from the non-marine Torridon Group are remarkably preserved by a combination of clay minerals and phosphate, with clay minerals providing the highest fidelity of preservation. Fe-rich clay mostly occurs in narrow zones in contact with cellular material and is interpreted as an early microbially-mediated phase enclosing and replacing the most labile biological material. K-rich clay occurs within and exterior to cell envelopes, forming where the supply of Fe had been exhausted. Clay minerals inter-finger with calcium phosphate that co-precipitated with the clays in the sub-oxic zone of the lake sediments. This type of preservation was favoured in sulfate-poor environments where Fe-silicate precipitation could outcompete Fe-sulfide formation. This work shows that clay minerals can provide an exceptionally high fidelity of microfossil preservation and extends the known geological range of this fossilization style by almost 500 Ma. It also suggests that the best-preserved microfossils of this time may be found in low-sulfate environments

Detecting ancient life : Investigating the nature and origin of possible stromatolites and associated calcite from a one billion year old lake

ATB acknowledges the hospitality of the North West Highlands Geopark in July 2017. DW acknowledges funding from the Australian Research Council via the Future Fellowship scheme (FT 140100321).Peer reviewedPostprin

A possible billion-year-old holozoan with differentiated multicellularity.

Sediments of the Torridonian sequence of the Northwest Scottish Highlands contain a wide array of microfossils, documenting life in a non-marine setting a billion years ago (1 Ga).1, 2, 3, 4 Phosphate nodules from the Diabaig Formation at Loch Torridon preserve microorganisms with cellular-level fidelity,5,6 allowing for partial reconstruction of the developmental stages of a new organism, Bicellum brasieri gen. et sp. nov. The mature form of Bicellum consists of a solid, spherical ball of tightly packed cells (a stereoblast) of isodiametric cells enclosed in a monolayer of elongated, sausage-shaped cells. However, two populations of naked stereoblasts show mixed cell shapes, which we infer to indicate incipient development of elongated cells that were migrating to the periphery of the cell mass. These simple morphogenetic movements could be explained by differential cell-cell adhesion.7,8 In fact, the basic morphology of Bicellum is topologically similar to that of experimentally produced cell masses that were shown to spontaneously segregate into two distinct domains based on differential cadherin-based cell adhesion.9 The lack of rigid cell walls in the stereoblast renders an algal affinity for Bicellum unlikely: its overall morphology is more consistent with a holozoan origin. Unicellular holozoans are known today to form multicellular stages within complex life cycles,10, 11, 12, 13 so the occurrence of such simple levels of transient multicellularity seen here is consistent with a holozoan affinity. Regardless of precise phylogenetic placement, these fossils demonstrate simple cell differentiation and morphogenic processes that are similar to those seen in some metazoans today

Remarkable preservation of brain tissues in an Early Cretaceous iguanodontian dinosaur

It has become accepted in recent years that the fossil record can preserve labile tissues. We report here the highly detailed mineralization of soft tissues associated with a naturally occurring brain endocast of an iguanodontian dinosaur found in c. 133 Ma fluvial sediments of the Wealden at Bexhill, Sussex, UK. Moulding of the braincase wall and the mineral replacement of the adjacent brain tissues by phosphates and carbonates allowed the direct examination of petrified brain tissues. Scanning electron microscopy (SEM) imaging and computed tomography (CT) scanning revealed preservation of the tough membranes (meninges) that enveloped and supported the brain proper. Collagen strands of the meningeal layers were preserved in collophane. The blood vessels, also preserved in collophane, were either lined by, or infilled with, microcrystalline siderite. The meninges were preserved in the hindbrain region and exhibit structural similarities with those of living archosaurs. Greater definition of the forebrain (cerebrum) than the hindbrain (cerebellar and medullary regions) is consistent with the anatomical and implied behavioural complexity previously described in iguanodontian-grade ornithopods. However, we caution that the observed proximity of probable cortical layers to the braincase walls probably resulted from the settling of brain tissues against the roof of the braincase after inversion of the skull during decay and burial

Enhanced cellular preservation by clay minerals in 1 billion-year-old lakes

Organic-walled microfossils provide the best insights into the composition and evolution of the biosphere through the first 80 percent of Earth history. The mechanism of microfossil preservation affects the quality of biological information retained and informs understanding of early Earth palaeo-environments. We here show that 1 billion-year-old microfossils from the non-marine Torridon Group are remarkably preserved by a combination of clay minerals and phosphate, with clay minerals providing the highest fidelity of preservation. Fe-rich clay mostly occurs in narrow zones in contact with cellular material and is interpreted as an early microbially-mediated phase enclosing and replacing the most labile biological material. K-rich clay occurs within and exterior to cell envelopes, forming where the supply of Fe had been exhausted. Clay minerals inter-finger with calcium phosphate that co-precipitated with the clays in the sub-oxic zone of the lake sediments. This type of preservation was favoured in sulfate-poor environments where Fe-silicate precipitation could outcompete Fe-sulfide formation. This work shows that clay minerals can provide an exceptionally high fidelity of microfossil preservation and extends the known geological range of this fossilization style by almost 500 Ma. It also suggests that the best-preserved microfossils of this time may be found in low-sulfate environments.David Wacey, Martin Saunders, Malcolm Roberts, Sarath Menon, Leonard Green, Charlie Kong, Timothy Culwick, Paul Strother, Martin D. Brasie

The origin of multicellularity in cyanobacteria

Background: Cyanobacteria are one of the oldest and morphologically most diverse prokaryotic phyla on our planet. The early development of an oxygen-containing atmosphere approximately 2.45 - 2.22 billion years ago is attributed to the photosynthetic activity of cyanobacteria. Furthermore, they are one of the few prokaryotic phyla where multicellularity has evolved. Understanding when and how multicellularity evolved in these ancient organisms would provide fundamental information on the early history of life and further our knowledge of complex life forms. Results: We conducted and compared phylogenetic analyses of 16S rDNA sequences from a large sample of taxa representing the morphological and genetic diversity of cyanobacteria. We reconstructed ancestral character states on 10,000 phylogenetic trees. The results suggest that the majority of extant cyanobacteria descend from multicellular ancestors. Reversals to unicellularity occurred at least 5 times. Multicellularity was established again at least once within a single-celled clade. Comparison to the fossil record supports an early origin of multicellularity, possibly as early as the “Great Oxygenation Event” that occurred 2.45 - 2.22 billion years ago. Conclusions: The results indicate that a multicellular morphotype evolved early in the cyanobacterial lineage and was regained at least once after a previous loss. Most of the morphological diversity exhibited in cyanobacteria today —including the majority of single-celled species— arose from ancient multicellular lineages. Multicellularity could have conferred a considerable advantage for exploring new niches and hence facilitated the diversification of new lineages