A new nektaspid euarthropod from the Lower Ordovician strata of Morocco

International audienceNektaspids are Palaeozoic non-biomineralized euarthropods that were at the peak of their diversity during the Cambrian Period. Post-Cambrian nektaspids are a low-diversity group with only a few species described so far. Here we describe Tariccoia tazagurtensis , a new species of small-bodied nektaspid from the Lower Ordovician Fezouata Shale of Morocco. The new species differs from the type (and only other known) species from the Ordovician strata of Sardinia (Italy), Tariccoia arrusensis , in possessing more pointed genal angles, a cephalon with marginal rim, a pygidium with anterior margin curved forwards, a rounded posterior margin, and longer and more curved thoracic tergites. The two specimens of T. tazagurtensis sp. nov. show remains of digestive glands that are comparable to those seen in the Cambrian nektaspid Naraoia . The rare occurrence of T. tazagurtensis sp. nov. in the Fezouata Shale and the distribution of other liwiids suggest that these liwiids were originally minor members of open-marine communities during the Cambrian Period, and migrated into colder brackish or restricted seas during the Ordovician Period

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

Understanding ancient life: how Martin Brasier changed the way we think about the fossil record

Crucial to our understanding of life on Earth is the ability to judge the validity of claims of very ancient ‘fossils’. Martin Brasier's most important contribution to this debate was to establish a framework within which to discuss claims of the ‘oldest’ life. In particular, he made it clear that the burden of proof must fall on those making the claim of ancient life, not those refuting it. This led to his formulation of the concept of the continuum of morphologies produced by life and non-life and the considerable challenges of differentiating biogenesis from abiogenesis. Martin Brasier developed a set of criteria for distinguishing life from non-life and extended the use of many new high-resolution analytical techniques to palaeontological research. He was also renowned for his work on the Cambrian explosion and the origin of animals. Although he had spent much of his early career working on the geological context of these events, it was not until he returned to studying the Ediacaran and Cambrian periods in his later years that he began to apply this null hypothesis way of thinking to these other major transitions in the history of life. This led to him becoming involved in the development of a series of nested null hypotheses, his ‘cone of contention’, to analyse enigmatic fossils more generally. In short, Martin Brasier taught us how to formulate biological hypotheses in deep time, established the rules for how those hypotheses should be tested and championed a host of novel analytical techniques to gather the data required. As a consequence, future discussions of enigmatic specimens and very old fossils will be greatly enriched by his contributions

A novel tool to untangle the ecology and fossil preservation knot in exceptionally preserved biotas

Understanding the functioning of extinct ecosystems is a complicated knot of ecological, evolutionary, and preservational strands that must be untangled. For instance, anatomical and behavioral differences can profoundly alter fossilization pathways. This is particularly true in exceptionally preserved soft-bodied biotas that record the earliest phases of animal evolution during the Cambrian Explosion and the Ordovician Radiation. Herein, a novel method of data partitioning based on probabilistic modelling is developed to examine these processes for the Walcott Quarry, Burgess Shale, Canada (510Ma), and the Fezouata Shale, Morocco (c. 475Ma). The modelling shows that the mechanism for soft-tissue preservation in the Walcott Quarry is ecologically selective, favoring the endobenthos. This is not found in the Fezouata Shale. Taken in concert with bioturbation data, a new model of comparative preservation is developed based on sedimentary flow dynamics. This suggests that during the Cambrian Explosion and Ordovician Radiation the most exceptional fossils sites must still be calibrated against each other to understand the unfolding evolutionary events and the ecological structuring of ancient animal communities

Genetic mechanisms of critical illness in COVID-19.

Host-mediated lung inflammation is present1, and drives mortality2, in the critical illness caused by coronavirus disease 2019 (COVID-19). Host genetic variants associated with critical illness may identify mechanistic targets for therapeutic development3. Here we report the results of the GenOMICC (Genetics Of Mortality In Critical Care) genome-wide association study in 2,244 critically ill patients with COVID-19 from 208 UK intensive care units. We have identified and replicated the following new genome-wide significant associations: on chromosome 12q24.13 (rs10735079, P = 1.65 × 10-8) in a gene cluster that encodes antiviral restriction enzyme activators (OAS1, OAS2 and OAS3); on chromosome 19p13.2 (rs74956615, P = 2.3 × 10-8) near the gene that encodes tyrosine kinase 2 (TYK2); on chromosome 19p13.3 (rs2109069, P = 3.98 ×  10-12) within the gene that encodes dipeptidyl peptidase 9 (DPP9); and on chromosome 21q22.1 (rs2236757, P = 4.99 × 10-8) in the interferon receptor gene IFNAR2. We identified potential targets for repurposing of licensed medications: using Mendelian randomization, we found evidence that low expression of IFNAR2, or high expression of TYK2, are associated with life-threatening disease; and transcriptome-wide association in lung tissue revealed that high expression of the monocyte-macrophage chemotactic receptor CCR2 is associated with severe COVID-19. Our results identify robust genetic signals relating to key host antiviral defence mechanisms and mediators of inflammatory organ damage in COVID-19. Both mechanisms may be amenable to targeted treatment with existing drugs. However, large-scale randomized clinical trials will be essential before any change to clinical practice

Testing the protozoan hypothesis for Ediacaran fossils: a developmental analysis of Palaeopascichnus

The hypothesis that the Ediacara biota were giant protozoans is tested by considering the external morphology, internal organization, suggested fossil representatives and molecular phylogeny of the xenophyophores. From this analysis, we find no case to support a direct relationship. Rather, the xenophyophores are here regarded as a group of recently evolved Foraminifera and are hence unlikely to have a record from the Ediacaran Period. Further from the growth dynamics of Foraminifera, they are also unlikely to be related to the Palaeopascichnus organism. We also find significant distinctions in the growth dynamics of Palaeopascichnus and organisms usually referred to the Ediacara biota, such as Charnia and Dickinsonia. Developmental analysis of the Palaeopascichnus– central to the xenophyophore hypothesis – reveals unusual, protozoan features, including evidence for chaotic repair structures, for mergence of coeval forms, as well as complex bifurcations. These observations suggest that Palaeopascichnus is a body fossil of an unidentified protozoan but is unrepresentative of Ediacaran body construction, in general

The architecture of Ediacaran Fronds

Abstract: Ongoing discoveries of new rangeomorph fossils from the Ediacaran of Avalonia allow us to put forward a unified and approachable scheme for the description and phylogenetic analysis of frondose genera and their species. This scheme focuses upon the branching morphology of rangeomorph units. Our system has the advantage of being applicable at all visible scales of subdivision and is suitable for the study of isolated fragmentary specimens. The system is also free from hypothesis about biological affinity and avoids tectonically influenced features such as shape metrics. Using a set of twelve character states within this unified scheme, we here present emended diagnoses for Beothukis, Avalofractus, Bradgatia, Hapsidophyllas, Fractofusus, Trepassia and Charnia, together with a more extensive taxonomic treatment of the latter genus. For those forms that fall within the morphological spectrum between Trepassia and Beothukis, we introduce Vinlandia gen. nov. It is hoped that this scheme will provide a robust framework for future studies of rangeomorph ontogeny and evolution

Variations in preservation of exceptional fossils within concretions

Abstract Concretions are an interesting mode of preservation that can occasionally yield fossils with soft tissues. To properly interpret these fossils, an understanding of their fossilization is required. Probabilistic models are useful tools to identify variations between different Konservat-Lagerstätten that are separated spatially and temporally. However, the application of probabilistic modeling has been limited to Early Paleozoic Konservat-Lagerstätten preserved in shales. In this paper, the patterns of preservation of three concretionary Konservat-Lagerstätten—the Carboniferous Mazon Creek (USA) and Montceau-les-Mines (France), and the Silurian Herefordshire Lagerstätte (UK)—are analyzed using a statistical approach. It is demonstrated that the degree of biotic involvement, i.e., the degree to which a carcass dictates its own preservation, is connected to internal organ conditional probabilities—the probabilities of finding an internal organ associated with another structure such as biomineralized, sclerotized, cuticularized, or cellular body walls. In concretions that are externally forced with little biological mediation (e.g., Herefordshire), all internal organ conditional probabilities are uniform. As biological mediation in concretion formation becomes more pronounced, heterogeneities in conditional probabilities are introduced (e.g., Montceau-les-Mines and Mazon Creek). The three concretionary sites were also compared with previously investigated Konservat-Lagerstätten preserving fossils in shales to demonstrate how the developed probability framework aids in understanding the broad-scale functioning of preservation in Konservat-Lagerstätten

The oldest evidence of bioturbation on Earth: COMMENT

Here we question the conclusions of Rogov et al. (2012), who claim \ud to describe “the oldest evidence of bioturbation on Earth” in the form of \ud meniscate backfi lled burrows and escape traces from late Ediacaran car-\ud bonates of the Siberian Khatyspyt Formation. Because trace fossils can \ud constrain early Metazoan origins, and are used to defi ne the base of the \ud Cambrian Period (Brasier et al., 1994), such a signifi cant claim requires jus-\ud tifi cation by careful interpretation of the material, and critical analysis, both \ud of which appear wanting here. Although we agree that multiple biological \ud and ecological revolutions took place during the late Ediacaran Period, we \ud question whether those events can be tied to these problematic fossils