Further evidence for fungivory in the Lower Devonian (Lochkovian) of the Welsh Borderland, UK

The recent demonstrations that widespread mid-Palaeozoic Prototaxites and other nematophytes had fungal affinities indicate that terrestrial fungi were important elements in carbon cycling in the Early Devonian. Here, we provide evidence for their participation in the recycling of nutrients by early terrestrial invertebrates. Evidence is in the form of coprolites, both those associated with nematophytes or containing their fragmentary remains. Cylindrical coprolites consistently associated with fungal mats are placed in a new ichnospecies, Bacillafaex myceliorum. Their contents are granular to amorphous, suggestive of complete digestion of the ingested hyphae, with the inference of possession of chitinases in the digestive tracts of the consumers. A further single example comprises a cluster of cylindrical bodies attached to the lower surface of a Nematothallus fragment. Here, homogenisation was less complete, with traces of hyphae remaining. Terrestrial animal fossils have not been found at the locality, but scorpions, pseudoscorpions, Opiliones, mites, centipedes (carnivores) and millipedes, and Collembola (detritivores) have been recorded from the slightly younger Rhynie cherts. Studies of fungivory in extant arthropods have concentrated on Collembola and, to a lesser extent, mites, but their faecal pellets are much smaller than the fossil examples. Millipedes, based on body size and faeces of extant forms, are considered more realistic producers, but little is known about fungal feeding in these animals. Regardless of the affinities of the producers, the diversity in morphology, sizes, aggregations, and composition of nematophyte-containing examples suggests that fungivory was an important component of carbon cycling in early terrestrial ecosystems

Anatomically preserved Silurian 'nematophytes' from the Welsh Borderland (UK)

Stratified charcoalified fragments of thalloid organisms with tripartite tissue construction have been isolated from the basal member of the Upper Silurian (upper Ludlow) Downton Castle Sandstone Formation, exposed near Ludlow, Shropshire (England) and are considered to have had fungal affinity. They are divided into two major groups. The more novel of these is characterized by a superficial cortex separated from a basal layer of interweaving hyphae by an intermediate zone of compressed indeterminate tissue and members are placed in a new taxon, Tristratothallus ludfordensis. In the second, the intermediate zone comprises hyphae arranged at right angles to the cortex (termed palisade). Some members resemble the tissue construction of Nematothallus described from the Lower Devonian (Lochkovian) of the Welsh Borderland and considered to belong to fungi, some of which were lichenized. A further type, which shows remains of polysporic asci, is thought to represent a fragment of an apothecium (a disc-shaped ascoma of an ascomycete) of a pezizomycete and is the earliest such record. Yet others are characterized by a perforate cortex with occasional protruding hyphae, tissue construction of which was also recorded in the Lower Devonian of the Welsh Borderland and considered to display fungal characteristics. Coalified ‘black patches’ are common on bedding surfaces throughout the latest Silurian and Early Devonian and frequently are associated with basal embryophytes and tracheophytes. Those reported here are the oldest known with three-dimensional organization, studied via scanning electron microscopy (SEM) and attributed to fungi, and include some ascomycetes. Similar encrustations occur in even earlier rocks and may have been important constituents of the cryptogamic ground cover, which is postulated to have preceded higher plant life on land

Provenance and age of bacteria-like structures on mid-Palaeozoic plant fossils

Structures, termed microbioids, comforming to bacteria in size and shape (e.g. rods, spheres, chains and clusters of spheres) have been observed by field emission scanning electron microscopy (FE-SEM) on coalified Silurian and Lower Devonian spores, sporangia, cuticles and coprolites. Some were sectioned for transmission electron microscopy. The elemental composition of both microbioids and ‘substrates’ was investigated using a X-ray microanalysis system. These analyses combined with comparative studies on recent bacteria and cyanobacteria were undertaken to evaluate the biogenicity, nature and age of the microbioids. Spheres with a Si signature (0.03–0.5 μm diameter) and assumed composed of silica are interpreted as artefacts produced abiotically during the extraction procedures. A similar origin is proposed for hollow spheres that are composed of CaF2. These occur singly, in short chains simulating filaments, and in clusters. Considerable differences in size (0.2–2.0 μm diameter) and appearance relate to local variation in the chemical environment during extraction. Spheres (0.2–1.5 μm diameter), that lack a mineral signature, with a framboidal surface ornament and occur within sporangia are identified as by-products of spore development. A biotic origin is also postulated for C-containing rod-shaped structures (>3.1 μm long, <1.4 μm wide), some with collapsed surfaces, although comparisons with living bacteria indicate recent contamination. More elongate rod-shaped microbioids (<8.6 μm long, 1.2 μm wide) have been identified as detrital rutile crystals (TiO2). Minute naviculate structures (<2.2 μm long) resembling diatoms are of unknown origin but are probably composed of thorium hydroxide. Unmineralized filaments of cyanobacterial morphology are recent contaminants. Some of the sporangia and spore masses are partially covered by associations of fragmented sheets, interconnecting strands, rods and spheres that are interpreted as dehydrated biofilms. Being unmineralized they are probably also of recent origin, although they might have survived wild-fire along with the charcoalified mesofossils. Many of the structures illustrated here were initially identified casually as bacteria on the small fossils extracted for biodiversity studies using well-tried, conventional, palaeobotanical techniques. Our subsequent more detailed analyses have shown how such processes can produce artefacts that are morphological analogues of mineralized bacteria, leave residues that mimic bacterial shapes and, despite some efforts such as storage in dilute HCl to eliminate living bacteria, introduce contamination. They reinforce previous concerns that verification of the biogenicity and syngenicity of bacterial-like objects in ancient Earth and extra-terrestrial rocks should not only rely on size and morphological look-alikes, but must encompass a thorough understanding of fossilization processes and extraction techniques plus, ideally, other measures of biogenicity (e.g. biomarkers) and syngenicity

Piecing together the eophytes - a new group of ancient plants containing cryptospores

The earliest evidence for land plants comes from dispersed cryptospores from the Ordovician, which dominated assemblages for 60 million years. Direct evidence of their parent plants comes from minute fossils in Welsh Borderland Upper Silurian to Lower Devonian rocks. We recognize a group that had forking, striated axes with rare stomata terminating in valvate sporangia containing permanent cryptospores, but their anatomy was unknown especially regarding conducting tissues. Charcoalified fossils extracted from the rock using HF were selected from macerates and observed using scanning electron microscopy. Promising examples were split for further examination and compared with electron micrographs of the anatomy of extant bryophytes. Fertile fossil axes possess central elongate cells with thick walls bearing globules, occasional strands and plasmodesmata-sized pores. The anatomy of these cells best matches desiccation-tolerant food-conducting cells (leptoids) of bryophytes. Together with thick-walled epidermal cells and extremely small size, these features suggest that these plants were poikilohydric. Our new data on conducting cells confirms a combination of characters that distinguish the permanent cryptospore-producers from bryophytes and tracheophytes. We therefore propose the erection of a new group, here named the Eophytidae (eophytes)

Earliest record of transfer cells in Lower Devonian plants

Key sources of information on the nature of early terrestrial ecosystems are the fossilized remains of plants and associated organic encrustations, which are interpreted as either biofilms, biological soil crusts or lichens. The hypothesis that some of these encrustations might be the remains of the thalloid gametophytes of embryophytes provided the stimulus for this investigation. Fossils preserved in charcoal were extracted from Devonian Period (Lochkovian Stage, c. 410–419 Myr old) sediments at a geological site in Shropshire (UK). Scanning electron micrographs (SEMs) of the fossils were compared with new and published SEMs of extant bryophytes and tracheophytes, respectively. One specimen was further prepared and imaged by transmission electron microscopy. Fossils of thalloid morphology were composed almost entirely of cells with labyrinthine ingrowths; these also were present in fossils of axial morphology where they were associated with putative food-conducting cells. Comparison with modern embryophytes demonstrates that these distinctive cells are transfer cells (TCs). Our fossils provide by far the earliest geological evidence of TCs. They also show that some organic encrustations are the remains of thalloid land plants and that these are possibly part of the life cycle of a newly recognized group of plants called the eophyte

Association between rheumatoid arthritis disease activity, progression of functional limitation and long-term risk of orthopaedic surgery : Combined analysis of two prospective cohorts supports EULAR treat to target DAS thresholds

Objectives: To examine the association between disease activity in early rheumatoid arthritis (RA), functional limitation and long-term orthopaedic episodes. Methods: Health Assessment Questionnaire (HAQ) disability scores were collected from two longitudinal early RA inception cohorts in routine care; Early Rheumatoid Arthritis Study and Early Rheumatoid Arthritis Network from 1986 to 2012. The incidence of major and intermediate orthopaedic surgical episodes over 25 years was collected from national data sets. Disease activity was categorised by mean disease activity score (DAS28) annually between years 1 and 5; remission (RDAS≤2.6), low (LDAS>2.6-3.2), low-moderate (LMDAS≥3.2-4.19), high-moderate (HMDAS 4.2-5.1) and high (HDAS>5.1). Results: Data from 2045 patients were analysed. Patients in RDAS showed no HAQ progression over 5 years, whereas there was a significant relationship between rising DAS28 category and HAQ at 1 year, and the rate of HAQ progression between years 1 and 5. During 27 986 person-years follow-up, 392 intermediate and 591 major surgeries were observed. Compared with the RDAS category, there was a significantly increased cumulative incidence of intermediate surgery in HDAS (OR 2.59 CI 1.49 to 4.52) and HMDAS (OR 1.8 CI 1.05 to 3.11) categories, and for major surgery in HDAS (OR 2.48 CI 1.5 to 4.11), HMDAS (OR 2.16 CI 1.32 to 3.52) and LMDAS (OR 2.07 CI 1.28 to 3.33) categories. There was no significant difference in HAQ progression or orthopaedic episodes between RDAS and LDAS categories. Conclusions: There is an association between disease activity and both poor function and long-term orthopaedic episodes. This illustrates the far from benign consequences of persistent moderate disease activity, and supports European League Against Rheumatism treat to target recommendations to secure low disease activity or remission in all patients.Peer reviewedFinal Published versio

Fertile Prototaxites taiti: a basal ascomycete with inoperculate, polysporous asci lacking croziers

The affinities of Prototaxites have been debated ever since its fossils, some attaining tree-trunk proportions, were discovered in Canadian Lower Devonian rocks in 1859. Putative assignations include conifers, red and brown algae, liverworts and fungi (some lichenised). Detailed anatomical investigation led to the reconstruction of the type species, P. logani, as a giant sporophore (basidioma) of an agaricomycete (= holobasidiomycete), but evidence for its reproduction remained elusive. Tissues associated with P. taiti in the Rhynie chert plus charcoalified fragments from southern Britain are investigated here to describe the reproductive characters and hence affinities of Prototaxites. Thin sections and peels (Pragian Rhynie chert, Aberdeenshire) were examined using light and confocal microscopy; Přídolí and Lochkovian charcoalified samples (Welsh Borderland) were liberated from the rock and examined with scanning electron microscopy. Prototaxites taiti possessed a superficial hymenium comprising an epihymenial layer, delicate septate paraphyses, inoperculate polysporic asci lacking croziers and a subhymenial layer composed predominantly of thin-walled hyphae and occasional larger hyphae. Prototaxites taiti combines features of extant Taphrinomycotina (Neolectomycetes lacking croziers) and Pezizomycotina (epihymenial layer secreted by paraphyses) but is not an ancestor of the latter. Brief consideration is given to its nutrition and potential position in the phylogeny of the Ascomycota

Novel conducting tissues in Lower Devonian plants

Elongate cells presumed to comprise water-conducting tissues are described from the central regions of short lengths of two naked, stomatiferous, coalified, axial fossils from Lochkovian (Lower Devonian) fluvial rocks in the Welsh Borderland. In one, a discrete central strand is predominantly composed of uniformly thickened cells that are compared with central tissues in coeval plants, e.g. Aglaophyton, and the hydroids of extant mosses. The other has at least two types of cells with pits of plasmodesmata dimensions that perforate only the inner layer of a bilayered wall. These are compared with liverwort and Takakia hydroids and the coeval S-type tracheids that characterize the Rhyniopsida. The affinities of the two axes remain equivocal. The relevance of plasmodesmata-derived pits to the evolution of diversity in water-conducting elements in early cmbryophytes is discussed