The early evolution of land plants, from fossils to genomics: a commentary on Lang (1937) ‘On the plant-remains from the Downtonian of England and Wales'

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Biologically mediated weathering in modern cryptogamic ground covers and the early Paleozoic fossil record

Specific micro-weathering features and biochemically derived residues formed by living organisms can be used as biomarkers to infer the presence of biological communities within sedimentary units of ancient ecosystems. We examined basaltic soil minerals from modern cryptogamic ground covers (CGCs) in Iceland and compared these with two early Paleozoic fossil systems. Nine biologically mediated weathering features (BWFs) were identified in modern soils including micron-scale surface trenching and penetrative tunnels, which are attributed to the actions of bacteria, fungi and exudates. Specific BWFs are associated with Fe residues, and with Fe-rich bio-precipitated nodules. Further, putative comparable features and Fe enrichment are identified in palaeosols from the late Silurian (Llansteffan, south Wales) and the Early Devonian (Rhynie chert, Scotland). Although we are cautious about attributing biological affinity to individual isolated features, our results demonstrate the potential of using multiple BWF types as a collective together with their chemical signatures as new proxies to understand community structure and interactions in early terrestrial ecosystems. This new information is the first evidence of interactions between ancient CGC-like organisms and substrate or soil inorganic components in the fossil record, and demonstrates the ability of CGC-like biospheres to contribute to mineral weathering, soil development and biogeochemical cycling during the early Paleozoic. Supplementary material: Fieldwork geomorphological information and triplot SEM-EDS data are available at https://doi.org/10.6084/m9.figshare.c.437371

New model systems for early land plant evolution (w16-05) Vienna, Austria, 22 - 24 June 2016

Microbial communities have existed on land since at least the Neoarchean (2800 to 2500 million years), but fossil evidence indicates that the ancestors of land plants first appeared much later during the mid-Ordovician some 470 million years ago. These latter communities probably comprised varied and mixed associations of Archaea, Bacteria, arthropods, lichens, fungi, green algae and extinct land plants called ‘cryptophytes’. Little is known about the cryptophytes, but emerging evidence from fossil charcoal records minute sporophytes at the bryophyte level of complexity but with novel combinations of characteristics. Some are known to contain spores dispersed as tetrads and dyads suggesting that significant differences in sporogenesis operated in some early extinct lineages. The most intact and earliest well-preserved fossil ecosystem is the 407 million year old Rhynie Chert (Scotland). Here, plants were fossilised near to their sites of growth preserving soft tissues and organism associations. Such fossils provide unparalleled insights into the evolution of major organ systems in stem group vascular plants and lycophytes, including roots, shoots, leaves, vascular system and reproductive structures. They are helping us to understand how key plant organs evolved from precursor structures, to disentangle homology from homoplasy, to better reconstruct early life cycle evolution, and to learn about the co-evolution of plants and their fungal symbionts.Abstract of oral presentation given at the EMBO Workshop New Model Systems for Early Plant Evolution, June 2016, Vienna

A New Chytridiomycete Fungus Intermixed with Crustacean Resting Eggs in a 407-Million-Year-Old Continental Freshwater Environment

Copyright: © 2016 Strullu-Derrien et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Fragments of the earliest land plants

The earliest fossil evidence for land plants comes from microscopic dispersed spores. These microfossils are abundant and widely distributed in sediments, and the earliest generally accepted reports are from rocks of mid-Ordovician age (Llanvirn, 475 million years ago). Although distribution, morphology and ultrastructure of the spores indicate that they are derived from terrestrial plants, possibly early relatives of the bryophytes, this interpretation remains controversial as there is little in the way of direct evidence for the parent plants. An additional complicating factor is that there is a significant hiatus between the appearance of the first dispersed spores and fossils of relatively complete land plants (megafossils): spores predate the earliest megafossils (Late Silurian, 425 million year ago) by some 50 million years. Here we report the description of spore-containing plant fragments from Ordovician rocks of Oman. These fossils provide direct evidence for the nature of the spore-producing plants. They confirm that the earliest spores developed in large numbers within sporangia, providing strong evidence that they are the fossilized remains of bona fide land plants. Furthermore, analysis of spore wall ultrastructure supports liverwort affinities

Did Captain Scott's Terra Nova Expedition discover fossil Nothofagus in Antarctica?

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Correlative Microscopy: a tool for understanding soil weathering in modern analogues of early terrestrial biospheres

Correlative imaging provides a method of investigating complex systems by combining analytical (chemistry) and imaging (tomography) information across dimensions (2D-3D) and scales (centimetres-nanometres). We studied weathering processes in a modern cryptogamic ground cover from Iceland, containing early colonizing, and evolutionary ancient, communities of mosses, lichens, fungi, and bacteria. Targeted multi-scale X-ray Microscopy of a grain in-situ within a soil core revealed networks of surficial and internal features (tunnels) originating from organic-rich surface holes. Further targeted 2D grain characterisation by optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (SEM–EDS), following an intermediate manual correlative preparation step, revealed Fe-rich nodules within the tunnels. Finally, nanotomographic imaging by focussed ion beam microscopy (FIB-SEM) revealed coccoid and filamentous-like structures within subsurface tunnels, as well as accumulations of Fe and S in grain surface crusts, which may represent a biological rock varnish/glaze. We attribute these features to biological processes. This work highlights the advantages and novelty of the correlative imaging approach, across scales, dimensions, and modes, to investigate biological weathering processes. Further, we demonstrate correlative microscopy as a means of identifying fingerprints of biological communities, which could be used in the geologic rock record and on extra-terrestrial bodies