Decline and fall of the Ediacarans: late-Neoproterozoic extinctions and the rise of the modern biosphere

The end-Neoproterozoic transition marked a gradual but permanent shift between distinct configurations of Earth's biosphere. This interval witnessed the demise of the enigmatic Ediacaran Biota, ushering in the structured trophic webs and disparate animal body plans of Phanerozoic ecosystems. However, little consensus exists on the reality, drivers, and macroevolutionary implications of end-Neoproterozoic extinctions. Here we evaluate potential drivers of late-Neoproterozoic turnover by addressing recent findings on Ediacaran geochronology, the persistence of classical Ediacaran macrobionts into the Cambrian, and the existence of Ediacaran crown-group eumetazoans. Despite renewed interest in the possibility of Phanerozoic-style ‘mass extinctions’ in the latest Neoproterozoic, our synthesis of the available evidence does not support extinction models based on episodic geochemical triggers, nor does it validate simple ecological interpretations centred on direct competitive displacement. Instead, we argue that the protracted and indirect effects of early bilaterian innovations, including escalations in sediment engineering, predation, and the largely understudied impacts of reef-building, may best account for the temporal structure and possible selectivity of late-Neoproterozoic extinctions. We integrate these processes into a generalised model of early eumetazoan-dominated ecologies, charting the disruption of spatial and temporal isotropy on the Ediacaran benthos as a consequence of diversifying macrofaunal interactions. Given the nature of resource distribution in Ediacaran ecologies, the continuities among Ediacaran and Cambrian faunas, and the convergent origins of ecologically disruptive innovations among bilaterians we suggest that the rise of Phanerozoic-type biotas may have been unstoppable

Filamentous Connections between Ediacaran Fronds.

Fossils of the Ediacaran macrobiota (∼571-539 mya) record phylogenetically diverse marine palaeocommunities, including early animals, which pre-date the "Cambrian Explosion" [1-4]. Benthic forms with a frondose gross morphology, assigned to the morphogroups Rangeomorpha [5] and Frondomorpha (see also Arboreomorpha) [6-8], are among the most temporally wide-ranging and environmentally tolerant members of the Ediacaran macrobiota [6] and dominated deep-marine ecosystems ∼571-560 mya [9-11]. Investigations into the morphology [12-14], palaeoecology [10, 15, 16], reproductive strategies [17, 18], feeding methods [9, 19], and morphogenesis of frondose taxa together constrain their phylogenetic position to the metazoan (for Rangeomorpha) or eumetazoan (e.g., Arborea) total groups [14, 20], but tighter constraint is currently lacking. Here, we describe fossils of abundant filamentous organic structures preserved among frond-dominated fossil assemblages in Newfoundland (Canada). The filaments constitute a prominent component of the ecosystems, and exhibit clear physical associations with at least seven frondose taxa. Individual specimens of one uniterminal rangeomorph taxon appear to be directly connected by filaments across distances of centimeters to meters. Such physical linkages are interpreted to reflect evidence for stolonic connections: a conclusion with potential implications for the phylogenetic placement and palaeoecology of frondose organisms. Consideration of extant stoloniferous organisms suggests that Ediacaran frondose taxa were likely clonal and resurrects the possibility that they may have been colonial (e.g., [21, 22]). VIDEO ABSTRACT.NERC National Geographic Geological Society of London Cambridge Philosophical Societ

Immigration University Clinics and regulation: a working case study

This paper seeks to introduce readers to the regulation of immigration advice, and how this can work in practice in clinical legal education.  The case study of Queen Mary Legal Advice Centre demonstrates that although the statute does not ideally seem to fit with the regulation of university law clinics, it is possible to be compliant.  Far from being a negative aspect, regulation in these unique legal advice settings can actually provide a rich ethical learning environment and produce well rounded future lawyers

Modularity and overcompensatory growth in Ediacaran rangeomorphs demonstrate early adaptations for coping with environmental pressures

The first known diverse, complex, macroscopic benthic marine ecosystems (late Ediacaran, ca. 571-541 Ma) were dominated by the Rangeomorpha, an enigmatic group of extinct frondose eukaryotes that are candidate early metazoans[1,2]. The group is characterised by a self-similar branching architecture that was likely optimised for exchange, but nearly every other aspect of their biology is contentious[2–4]. We report locally-enhanced, aberrant growth (“eccentric branching”) in a stalked, multifoliate rangeomorph – Hylaecullulus fordi n. gen., n. sp. – from Charnwood Forest (UK), confirming the presence of true biological modularity within the group. Random branches achieve unusually large proportions and mimic the architecture of their parent branch, rather than that of their neighbours (the norm). Their locations indicate exceptional growth at existing loci, rather than insertion at new sites. Analogous over-compensatory branching in extant modular organisms requires the capacity to orchestrate growth at specific sites, and occurs most frequently in response to damage or environmental stress, allowing regeneration towards optimum morphology[e.g. 5–7]. Its presence in rangeomorphs indicates a hitherto unappreciated level of control to their growth plan, a previously unrecognised form of morphological plasticity within the group, and an ability to actively respond to external physical stimuli. The trait would have afforded rangeomorphs resilience to fouling and abrasion, partially accounting for their wide environmental tolerance, and may have pre-adapted them to withstand predation, weakening this argument for their extinction. Our findings highlight that multiple, phylogenetically disparate, clades first achieved large size through modularity

Learning From Coalitions' Efforts to Promote Equity and Justice.

Coalitions and collaboratives are working to address many of the most pressing contemporary health and social issues. The articles in this special issue provide numerous insights into these complex collaborative processes across different contexts and focal issues. All emphasize and scrutinize the strategies that groups are using in their work. These strategies seek to navigate not only conventional notions of effectiveness but also the challenges of pursuing greater equity and justice. In this concluding article, we distill some of the key insights from these articles as a collective. This special issue on collaborating for equity and justice can serve as a launching point for new efforts by coalitions and researchers pursuing policy, systems, and structural changes, particularly those intent on addressing root causes of health and social disparities

Construction of a "mutagenesis cartridge" for poliovirus genome-linked viral protein: Isolation and characterization of viable and nonviable mutants

By following a strategy of genetic analysis of poliovirus, we have constructed a synthetic "mutagenesis cartridge" spanning the genome-linked viral protein coding region and flanking cleavage sites in an infectious cDNA clone of the type 1 (Mahoney) genome. The insertion of new restriction sites within the infectious clone has allowed us to replace the wild-type sequences with short complementary pairs of synthetic oligonucleotides containing various mutations. A set of mutations have been made that create methionine codons within the genome-linked viral protein region. The resulting viruses have growth characteristics similar to wild type. Experiments that led to an alteration of the tyrosine residue responsible for the linkage to RNA have resulted in nonviable virus. In one mutant, proteolytic processing assayed in vitro appeared unimpaired by the mutation. We suggest that the position of the tyrosine residue is important for genome-linked viral protein function(s)

Feasibility of sedimentation strategies for the Mekong delta to counterbalance relative sea-level rise

As one of the largest deltas in the world, the Mekong delta is home to over 17 million people and supports internationally important agriculture. Recently deposited sediment compacts and causes subsidence in deltas, so they require regular sediment input to maintain elevation relative to sea level. These processes are complicated by human activities, which prevent sediment deposition indirectly through reducing fluvial sediment supply and directly through the construction of flood defence infrastructure on deltas, impeding floods which deliver sediment to the land. Additionally, anthropogenic activities increase the rate of subsidence through the extraction of groundwater and other land-use practices. This research shows the potential for fluvial sediment delivery to compensate for sea-level rise and subsidence in the Mekong delta over the 21st century. We use detailed elevation data and subsidence scenarios in combination with regional sea-level rise and fluvial sediment flux projections to quantify the potential for maintaining elevation relative to sea level in the Mekong delta. We present four examples of localised sedimentation scenarios in specific areas, for which we quantified the potential effectiveness of fluvial sediment deposition for offsetting relative sea-level rise. The presented sediment-based adaptation strategies are complicated by existing land use, therefore a change in water and sediment management is required to effectively use natural resources and employ these adaptation methods. The presented approach could be an exemplar to assess sedimentation strategy feasibility in other delta systems worldwide that are under threat from sea-level rise. This research shows the potential for fluvial sediment delivery to compensate for sea-level rise and subsidence in the Mekong delta over the 21st century. We use detailed elevation data and subsidence scenarios in combination with regional sea-level rise and fluvial sediment flux projections to quantify the potential for maintaining elevation relative to sea level in the Mekong delta. We present four examples of localised sedimentation scenarios in specific areas, for which we quantified the potential effectiveness of fluvial sediment deposition for offsetting relative sea-level rise. The presented sediment-based adaptation strategies are complicated by existing land use, therefore a change in water and sediment management is required to effectively use natural resources and employ these adaptation methods. The presented approach could be an exemplar to assess sedimentation strategy feasibility in other delta systems worldwide that are under threat from sea-level rise

Cambrian stem-group ambulacrarians and the nature of the ancestral deuterostome

Deuterostomes are characterized by some of the most widely divergent body plans in the animal kingdom. These striking morphological differences have hindered efforts to predict ancestral characters, with the origin and earliest evolution of the group remaining ambiguous. Several iconic Cambrian fossils have been suggested to be early deuterostomes and hence could help elucidate ancestral character states. However, their phylogenetic relationships are controversial. Here, we describe new, exceptionally preserved specimens of the discoidal metazoan Rotadiscus grandis from the early Cambrian Chengjiang biota of China. These reveal a previously unknown double spiral structure, which we interpret as a chordate-like covering to a coelomopore, located adjacent to a horseshoe-shaped tentacle complex. The tentacles differ in key aspects from those seen in lophophorates and are instead more similar to the tentacular systems of extant pterobranchs and echinoderms. Thus, Rotadiscus exhibits a chimeric combination of ambulacrarian and chordate characters. Phylogenetic analyses recover Rotadiscus and closely related fossil taxa as stem ambulacrarians, filling a significant morphological gap in the deuterostome tree of life. These results allow us to reconstruct the ancestral body plans of major clades of deuterostomes, revealing that key traits of extant forms, such as a post-anal region, gill bars, and a U-shaped gut, evolved through convergence