Mass extinctions and supernova explosions

A nearby supernova (SN) explosion could have negatively influenced life on Earth, maybe even been responsible for mass extinctions. Mass extinction poses a significant extinction of numerous species on Earth, as recorded in the paleontologic, paleoclimatic, and geological record of our planet. Depending on the distance between the Sun and the SN, different types of threats have to be considered, such as ozone depletion on Earth, causing increased exposure to the Sun's ultraviolet radiation, or the direct exposure of lethal x-rays. Another indirect effect is cloud formation, induced by cosmic rays in the atmosphere which result in a drop in the Earth's temperature, causing major glaciations of the Earth. The discovery of highly intensive gamma ray bursts (GRBs), which could be connected to SNe, initiated further discussions on possible life-threatening events in Earth's history. The probability that GRBs hit the Earth is very low. Nevertheless, a past interaction of Earth with GRBs and/or SNe cannot be excluded and might even have been responsible for past extinction events.Comment: Chapter for forthcoming book: Handbook of Supernovae, P. Murdin and A. Alsabeti (eds.), Springer International Publishing (in press

Functional diversity of marine ecosystems after the Late Permian mass extinction event

Article can be accessed from http://www.nature.com/ngeo/journal/v7/n3/full/ngeo2079.htmlThe Late Permian mass extinction event was the most severe such crisis of the past 500 million years and occurred during an episode of global warming. It is assumed to have had significant ecological impact, but its effects on marine ecosystem functioning are unknown and the patterns of marine recovery are debated. We analysed the fossil occurrences of all known Permian-Triassic benthic marine genera and assigned each to a functional group based on their inferred life habit. We show that despite the selective extinction of 62-74% of marine genera there was no significant loss of functional diversity at the global scale, and only one novel mode of life originated in the extinction aftermath. Early Triassic marine ecosystems were not as ecologically depauperate as widely assumed, which explains the absence of a Cambrian-style Triassic radiation in higher taxa. Functional diversity was, however, significantly reduced in particular regions and habitats, such as tropical reefs, and at these scales recovery varied spatially and temporally, probably driven by migration of surviving groups. Marine ecosystems did not return to their pre-extinction state, however, and radiation of previously subordinate groups such as motile, epifaunal grazers led to greater functional evenness by the Middle Triassic

Mass extinctions drove increased global faunal cosmopolitanism on the supercontinent Pangaea

Mass extinctions have profoundly impacted the evolution of life through not only reducing taxonomic diversity but also reshaping ecosystems and biogeographic patterns. In particular, they are considered to have driven increased biogeographic cosmopolitanism, but quantitative tests of this hypothesis are rare and have not explicitly incorporated information on evolutionary relationships. Here we quantify faunal cosmopolitanism using a phylogenetic network approach for 891 terrestrial vertebrate species spanning the late Permian through Early Jurassic. This key interval witnessed the Permian–Triassic and Triassic–Jurassic mass extinctions, the onset of fragmentation of the supercontinent Pangaea, and the origins of dinosaurs and many modern vertebrate groups. Our results recover significant increases in global faunal cosmopolitanism following both mass extinctions, driven mainly by new, widespread taxa, leading to homogenous ‘disaster faunas’. Cosmopolitanism subsequently declines in post-recovery communities. These shared patterns in both biotic crises suggest that mass extinctions have predictable influences on animal distribution and may shed light on biodiversity loss in extant ecosystems

The influences of nursing transformational leadership style on the quality of nurses’ working lives in Taiwan: a cross-sectional quantitative study

- Background: Taiwan’s NHI system is one of the most successful health care models for countries around the globe. However, little research has demonstrated the mental health issues associated with nursing transformational leadership style under the NHI system, especially in the quality of nurses’ working lives in Taiwan. It is important to know the relationship between transformational leadership style and the mental health of nurses, organisational commitment and job satisfaction. The research aimed to understand the influences of nursing transformational leadership style on the quality of nurses’ working lives in Taiwan. The research hypothesis was that transformational leadership styles would have positive influence on the quality of nurses’ working lives. - Methods: This was a cross-sectional quantitative study. Nurses from each type of hospital ownership (private, public and religious) were recruited. Participation was voluntary and signed informed consent was obtained. The inclusion criteria were nurses with at least one year’s work experience in the hospitals. Self-administrated questionnaires were used. A total of 807 participants were contacted and 651 questionnaires were fully completed (response rate 80.7 %). A theory driven model was used to test the research hypotheses using structural equation modelling performed with AMOS 16.0. - Results: Transformational leadership contributes significantly to supervisor support. Workplace support, particularly from the supervisor, is an important mediator variable that explains the relationship between transformational leadership and job satisfaction. Organisational commitment was the strongest factor relevant to the general health well-being in Taiwanese nurses than job satisfaction. The hypothesized positive relationships between transformational leadership and all variables were supported by the data. - Conclusions: Our findings have important consequences for organisational health. Our model demonstrates a complete picture of the work relationships on the quality of nurses’ working lives. The results provided information about the subordinates’ perceptions of transformational nursing leadership styles and mental health outcomes in different hospital settings, as well as identified organisational factors that could improve the quality of nurses’ working lives

Geographic range did not confer resilience to extinction in terrestrial vertebrates at the end-Triassic crisis

Rates of extinction vary greatly through geological time, with losses particularly concentrated in mass extinctions. Species duration at other times varies greatly, but the reasons for this are unclear. Geographical range correlates with lineage duration amongst marine invertebrates, but it is less clear how far this generality extends to other groups in other habitats. It is also unclear whether a wide geographical distribution makes groups more likely to survive mass extinctions. Here we test for extinction selectivity amongst terrestrial vertebrates across the end-Triassic event. We demonstrate that terrestrial vertebrate clades with larger geographical ranges were more resilient to extinction than those with smaller ranges throughout the Triassic and Jurassic. However, this relationship weakened with increasing proximity to the end-Triassic mass extinction, breaking down altogether across the event itself. We demonstrate that these findings are not a function of sampling biases; a perennial issue in studies of this kind

Broad-Scale Patterns of Late Jurassic Dinosaur Paleoecology

There have been numerous studies on dinosaur biogeographic distribution patterns. However, these distribution data have not yet been applied to ecological questions. Ecological studies of dinosaurs have tended to focus on reconstructing individual taxa, usually through comparisons to modern analogs. Fewer studies have sought to determine if the ecological structure of fossil assemblages is preserved and, if so, how dinosaur communities varied. Climate is a major component driving differences between communities. If the ecological structure of a fossil locality is preserved, we expect that dinosaur assemblages from similar environments will share a similar ecological structure.This study applies Ecological Structure Analysis (ESA) to a dataset of 100+ dinosaur taxa arranged into twelve composite fossil assemblages from around the world. Each assemblage was assigned a climate zone (biome) based on its location. Dinosaur taxa were placed into ecomorphological categories. The proportion of each category creates an ecological profile for the assemblage, which were compared using cluster and principal components analyses. Assemblages grouped according to biome, with most coming from arid or semi-arid/seasonal climates. Differences between assemblages are tied to the proportion of large high-browsing vs. small ground-foraging herbivores, which separates arid from semi-arid and moister environments, respectively. However, the effects of historical, taphonomic, and other environmental factors are still evident.This study is the first to show that the general ecological structure of Late Jurassic dinosaur assemblages is preserved at large scales and can be assessed quantitatively. Despite a broad similarity of climatic conditions, a degree of ecological variation is observed between assemblages, from arid to moist. Taxonomic differences between Asia and the other regions demonstrate at least one case of ecosystem convergence. The proportion of different ecomorphs, which reflects the prevailing climatic and environmental conditions present during fossil deposition, may therefore be used to differentiate Late Jurassic dinosaur fossil assemblages. This method is broadly applicable to different taxa and times, allowing one to address questions of evolutionary, biogeographic, and climatic importance

The multi-peak adaptive landscape of crocodylomorph body size evolution

Background: Little is known about the long-term patterns of body size evolution in Crocodylomorpha, the > 200-million-year-old group that includes living crocodylians and their extinct relatives. Extant crocodylians are mostly large-bodied (3–7 m) predators. However, extinct crocodylomorphs exhibit a wider range of phenotypes, and many of the earliest taxa were much smaller ( Results: Crocodylomorphs reached an early peak in body size disparity during the Late Jurassic, and underwent an essentially continual decline since then. A multi-peak Ornstein-Uhlenbeck model outperforms all other evolutionary models fitted to our data (including both uniform and non-uniform), indicating that the macroevolutionary dynamics of crocodylomorph body size are better described within the concept of an adaptive landscape, with most body size variation emerging after shifts to new macroevolutionary regimes (analogous to adaptive zones). We did not find support for a consistent evolutionary trend towards larger sizes among lineages (i.e., Cope’s rule), or strong correlations of body size with climate. Instead, the intermediate to large body sizes of some crocodylomorphs are better explained by group-specific adaptations. In particular, the evolution of a more aquatic lifestyle (especially marine) correlates with increases in average body size, though not without exceptions. Conclusions: Shifts between macroevolutionary regimes provide a better explanation of crocodylomorph body size evolution on large phylogenetic and temporal scales, suggesting a central role for lineage-specific adaptations rather than climatic forcing. Shifts leading to larger body sizes occurred in most aquatic and semi-aquatic groups. This, combined with extinctions of groups occupying smaller body size regimes (particularly during the Late Cretaceous and Cenozoic), gave rise to the upward-shifted body size distribution of extant crocodylomorphs compared to their smaller-bodied terrestrial ancestors.</p

Limited role of functional differentiation in early diversification of animals

The origin of most animal phyla and classes during the Cambrian explosion has been hypothesized to represent an ‘early burst’ of evolutionary exploration of functional ecological possibilities. However, the ecological history of marine animals has yet to be fully quantified, preventing an assessment of the early-burst model for functional ecology. Here we use ecological assignments for 18,621 marine animal genera to assess the relative timing of functional differentiation versus taxonomic diversification from the Cambrian to the present day. We find that functional diversity increased more slowly than would be expected given the history of taxonomic diversity. Contrary to previous inferences of rapid ecological differentiation from the early appearances of all well-fossilized phyla and classes, explicit coding of functional characteristics demonstrates that Cambrian genera occupied comparatively few modes of life. Functional diversity increased in the Ordovician and, especially, during the recoveries from the end-Permian and end-Cretaceous mass extinctions. Permanent shifts in the relationship between functional and taxonomic diversity following the era-bounding extinctions indicates a critical role for these biotic crises in coupling taxonomic and functional diversity