The full text of this mesosaur article is now available in pdf at the link. (Posted earlier as abstract only)
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Michel Laurin and Graciela PiÃeiro (2018)
Response From the Authors: A Reassessment of the Taxonomic Position of Mesosaurs, and a Surprising Phylogeny of Early Amniotes.
Frontiers in Earth Science 6:99
doi: 10.3389/feart.2018.00220
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Neil Brocklehurst, Emma M. Dunne, Daniel D. Cashmore & JÓrg FrÓbisch (2018)
Physical and environmental drivers of Paleozoic tetrapod dispersal across Pangaea.
Nature Communications 9, Article number: 5216Â
The Carboniferous and Permian were crucial intervals in the establishment of terrestrial ecosystems, which occurred alongside substantial environmental and climate changes throughout the globe, as well as the final assembly of the supercontinent of Pangaea. The influence of these changes on tetrapod biogeography is highly contentious, with some authors suggesting a cosmopolitan fauna resulting from a lack of barriers, and some identifying provincialism. Here we carry out a detailed historical biogeographic analysis of late Paleozoic tetrapods to study the patterns of dispersal and vicariance. A likelihood-based approach to infer ancestral areas is combined with stochastic mapping to assess rates of vicariance and dispersal. Both the late Carboniferous and the end-Guadalupian are characterised by a decrease in dispersal and a vicariance peak in amniotes and amphibians. The first of these shifts is attributed to orogenic activity, the second to increasing climate heterogeneity.
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Justin L. Penn, Curtis Deutsch, Jonathan L. Payne & Erik A. Sperling (2018)
Temperature-dependent hypoxia explains biogeography and severity of end-Permian marine mass extinction.
Science 362(6419): eaat1327
DOI: 10.1126/science.aat1327
Drivers of the âGreat Dyingâ
Though our current extinction crisis is substantial, it pales in comparison to the largest extinction in Earth's history, which occurred at the end of the Permian Period. Referred to as the "Great Dying," this event saw the loss of up to 96% of all marine species and 70% of terrestrial species. Penn et al. explored the extinction dynamics of the time using Earth system models in conjunction with physiological data across animal taxa (see the Perspective by Kump). They conclude that increased marine temperatures and reduced oxygen availability were responsible for a majority of the recorded extinctions. Because similar environmental alterations are predicted outcomes of current climate change, we would be wise to take note.
Structured Abstract
INTRODUCTION
Climate change triggered by volcanic greenhouse gases is hypothesized to have caused the largest mass extinction in Earthâs history at the end of the Permian Period (~252 million years ago). Geochemical evidence provides strong support for rapid global warming and accompanying ocean oxygen (O2) loss, but a quantitative link among climate, speciesâ traits, and extinction is lacking. To test whether warming and O2 loss can mechanistically account for the marine mass extinction, we combined climate model simulations with an established ecophysiological framework to predict the biogeographic patterns and severity of extinction. Those predictions were confirmed by a spatially explicit analysis of the marine fossil record.
RATIONALE
The impact of climate change on marine biodiversity depends on both its magnitude and on speciesâ diverse biological sensitivities. Tolerances of marine animals to warming and O2 loss are physiologically related and can be represented in a single metric: the ratio of temperature-dependent O2 supply and demand rates. This ratio, termed the Metabolic Index (Î), measures the environmental scope for aerobic activity and is governed by ocean conditions as well as thermal and hypoxia sensitivity traits that vary across species. If climate warming and O2 loss reduce Î below the species-specific minimum requirement for sustained ecological activity (Îcrit), the ocean would no longer support active aerobic metabolism and, by extension, long-term population persistence.
RESULTS
We simulated the greenhouse gasâdriven global warming at the end of the Permian using a model of Earthâs climate and coupled biogeochemical cycles that matches geochemical proxy data. The imposed increase in atmospheric greenhouse gas levels raises near-surface ocean temperatures by more than ~10ÂC and depletes global marine O2 levels by almost 80%.
To predict the impact of these changes on animal habitat and survival, we measured the frequencies of Metabolic Index traits in diverse living species and used them to define a set of model ecophysiotypes. We populated the model Permian ocean with each ecophysiotype wherever conditions provide viable habitat (Î â Îcrit), yielding an ocean with diverse, locally adapted ecophysiotypes throughout all regions. Across the climate transition, however, ocean warming increases the metabolic O2 demand amid declining supply; this removes large fractions of global aerobic habitat for the vast majority of ecophysiotypes and implies a high likelihood of extinction. We simulated the resulting mass extinction of ecophysiotypes and found a robust geographic pattern: Extinction intensity should have been lower in the tropics than at high latitudes. The cause of lower tropical extinction is that organisms initially inhabiting these warm, low-O2 environments can better exploit those conditions when they arise globally, whereas the habitats of more polar species disappear completely.
To test the geographic selectivity of the model extinction, we compared model predictions to spatially explicit reconstructions of genus extinction from the marine fossil record. We found that across diverse taxonomic groups, the observed extinction intensity indeed increases with latitude, consistent with the predicted signature of aerobic habitat loss. Comparison of the model to the fossil record implies that temperature-dependent hypoxia can account for more than half of the observed magnitude of regional extinction (i.e., extirpation).
CONCLUSION
Ocean warming and O2 loss simulated in an Earth System Model of end-Permian climate change imply widespread loss of aerobic habitat among animal types with diverse thermal and hypoxia tolerances. The resulting extinctions are predicted to select most strongly against higher-latitude species, whose biogeographic niche disappears globally. The combined physiological stresses of ocean warming and O2 loss largely account for the spatial pattern and magnitude of extinction observed in the fossil record of the âGreat Dying.â These results highlight the future extinction risk arising from a depletion of the oceanâs aerobic capacity that is already under way.
Abstract
Rapid climate change at the end of the Permian Period (~252 million years ago) is the hypothesized trigger for the largest mass extinction in Earthâs history. We present model simulations of the Permian/Triassic climate transition that reproduce the ocean warming and oxygen (O2) loss indicated by the geologic record. The effect of these changes on animal survival is evaluated using the Metabolic Index (Î), a measure of scope for aerobic activity governed by organismal traits sampled in diverse modern species. Modeled loss of aerobic habitat predicts lower extinction intensity in the tropics, a pattern confirmed with a spatially explicit analysis of the marine fossil record. The combined physiological stresses of ocean warming and O2 loss can account for more than half the magnitude of the âGreat Dying.â
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News:
Biggest extinction in Earthâs history caused by global warming leaving ocean animals gasping for breath
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Andrea Villa , Juan Abella, David M. Alba, Sergio AlmÃcija, Arnau Bolet, George D. Koufos, Fabien Knoll, Ãngel H. LujÃn, Jorge Morales, Josep M. Robles, Israel M. SÃnchez & Massimo Delfino (2018)
Revision of Varanus marathonensis (Squamata, Varanidae) based on historical and new material: morphology, systematics, and paleobiogeography of the European monitor lizards
PLoS ONE 13(12): e0207719.
Monitor lizards (genus Varanus) inhabited Europe at least from the early Miocene to the Pleistocene. Their fossil record is limited to about 40 localities that have provided mostly isolated vertebrae. Due to the poor diagnostic value of these fossils, it was recently claimed that all the European species described prior to the 21st century are not taxonomically valid and a new species, Varanus amnhophilis, was erected on the basis of fragmentary material including cranial elements, from the late Miocene of Samos (Greece). We re-examined the type material of Varanus marathonensis Weithofer, 1888, based on material from the late Miocene of Pikermi (Greece), and concluded that it is a valid, diagnosable species. Previously unpublished Iberian material from the Aragonian (middle Miocene) of Abocador de Can Mata (VallÃs-PenedÃs Basin, Barcelona) and the Vallesian (late Miocene) of Batallones (Madrid Basin) is clearly referable to the same species on a morphological basis, further enabling to provide an emended diagnosis for this species. Varanus amnhophilis appears to be a junior subjective synonym of V. marathonensis. On the basis of the most complete fossil Varanus skeleton ever described, it has been possible to further resolve the internal phylogeny of this genus by cladistically analyzing 80 taxa coded for 495 morphological and 5729 molecular characters. Varanus marathonensis was a large-sized species distributed at relatively low latitudes in both southwestern and southeastern Europe from at least MN7+8 to MN12. Our cladistic analysis nests V. marathonensis into an eastern clade of Varanus instead of the African clade comprising Varanus griseus, to which it had been related in the past. At least two different Varanus lineages were present in Europe during the Neogene, represented by Varanus mokrensis (early Miocene) and V. marathonensis (middle to late Miocene), respectively.
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Jasmine A. Nirody,Thomas Libby, Timothy J. Lee, Ardian Jusufi, David L. Hu &Â Robert J. Full (2018)
Geckos Race Across the Waterâs Surface Using Multiple Mechanisms.
Current Biology (advance online publication)
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Highlights
Geckos can race quadrupedally along the waterâs surface at close to land-running speeds
Intermediate-sized geckos use multiple strategies for interfacial locomotion
Mechanisms include surface slapping, body and tail undulation, and surface tension
Superhydrophobic skin likely reduces drag during semi-planing
Summary
Acrobatic geckos can sprint at high speeds over challenging terrain, scamper up the smoothest surfaces, rapidly swing underneath leaves, and right themselves in midair by swinging only their tails. From our field observations, we can add racing on the waterâs surface to the geckoâs list of agile feats. Locomotion at the air-water interface evolved in over a thousand species, including insects, fish, reptiles, and mammals. To support their weight, some larger-legged vertebrates use forces generated by vigorous slapping of the fluidâs surface followed by a stroke of their appendage, whereas smaller animals, like arthropods, rely on surface tension to walk on water. Intermediate-sized geckos (Hemidactylus platyurus) fall squarely between these two regimes. Here, we report the unique ability of geckos to exceed the speed limits of conventional surface swimming. Several mechanisms likely contribute in this intermediate regime. In contrast to bipedal basilisk lizards, geckos used a stereotypic trotting gait with all four limbs, creating air cavities during slapping to raise their head and anterior trunk above water. Adding surfactant to the water decreased velocity by half, confirming surface tensionâs role. The superhydrophobic skin could reduce drag during semi-planing. Geckos laterally undulated their bodies, including their submerged posterior trunk and tail, generating thrust for forward propulsion, much like water dragons and alligators. Geckos again remind us of the advantages of multi-functional morphologies providing the opportunity for multiple mechanisms for motion.
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Michelle N. Reichert, Paulo R. C. de Oliveira, George M. P. R. Souza, Henriette G. Moranza, Wilmer A. Z. Restan, Augusto S. Abe, Wilfried Klein & William K. Milsom (2018)
The respiratory mechanics of the yacare caiman (Caiman yacare Daudine).
Journal of Experimental Biology 2018 : jeb.193037
Âdoi: 10.1242/jeb.193037Â
The structure and function of crocodilian lungs are unique compared to other reptiles. We examine the extent to which this, and the semi-aquatic lifestyle of crocodilians affect their respiratory mechanics. We measured changes in intratracheal pressure in adult and juvenile caiman (Caiman yacare) during static and dynamic lung volume changes. Respiratory mechanics of juvenile caiman were additionally measured while floating in water and submerged at 30Â, 60Â, and 90Â to the water's surface. The static compliance of the juvenile pulmonary system (2.89Â0.22 mL cmH2O 100gâ1) was greater than that of adults (1.2Â0.41 ml cmH2O 100gâ1), suggesting that the system stiffens as the body wall becomes more muscular and keratinized in adults. For both age groups, the lungs were much more compliant than the body wall, offering little resistance to air flow (15.35 and 4.25 for lungs, versus 3.39 and 1.67 mL cmH2O 100gâ1 for body wall, in juveniles and adults respectively). Whole system dynamic mechanics decreased with increasing ventilation frequency (fR), but was unaffected by changes in tidal volume (VT). The vast majority of work of breathing was required to overcome elastic forces, however work to overcome resistive forces increased proportionally with fR. Work of breathing was higher in juvenile caiman submerged in water at 90Â, due to an increase in work to overcome both elastic and flow resistive forces. The lowest power of breathing was found to occur at high fR and low VT for any given minute ventilation (VÌE) in caiman of all ages.
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Bruce A. Young Â& Hilary S. Bierman (2018)
On the median pharyngeal valve of the American alligator (Alligator mississippiensis)
Journal of Morphology (advance online publication)
The middle ear cavities of crocodilians have complex connections with the pharyngeal lumen, including lateral and median components which both open into a single chamber located on the dorsal midline of the pharynx. This chamber and the surrounding softâtissue is herein termed the median pharyngeal valve. In the American alligator (Alligator mississippiensis) this valve opens, for a duration of 0.3 s, approximately every 120âs; the patency of the median pharyngeal valve was not influenced by either auditory stimuli or by submersing the alligator underwater. The median pharyngeal valve has an outer capsule of dense connective tissue and fibrocartilage and an inner âplugâ of loose connective tissue. These opposing surfaces are lined by respiratory epithelium and separated by a cavity that is continuous with the middle ear cavities and the pharyngeal lumen (through a central opening in the capsule termed the pore). The inner plug of the median pharyngeal valve is contacted by skeletal muscles positioned to serve as both elevators/retractors (which would open the valve) and elevators/protractors (which, in conjunction with gravity, would close the valve). Unlike other vertebrate valve systems, the median pharyngeal valve appears to function as a deformable ball check valve.
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Smart theropods....
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Morgan Wirthlin, Nicholas C.B. Lima, Rafael Lucas Muniz Guedes, Andrà E.R. Soares, Luiz Gonzaga P. Almeida, Nathalia P. Cavaleiro, Guilherme Loss de Morais, Anderson V. Chaves, Jason T. Howard, Marcus de Melo Teixeira, Patricia N. Schneider, FabrÃcio R. Santos, Michael C. Schatz, Maria Sueli Felipe, Cristina Y. Miyaki, Alexandre Aleixo, Maria P.C. Schneider, Erich D. Jarvis, Ana Tereza R. Vasconcelos, Francisco Prosdocimi & Claudio V. Mello (2018)
Parrot Genomes and the Evolution of Heightened Longevity and Cognition.
Current Biology (advance online publication)
Highlights
The blue-fronted Amazon, Amazona aestiva, and other parrots share unique novel genes
Convergent selection in long-lived birds suggests new lifespan-influencing genes
Parrot genomes share genetic changes related to genes critical for brain function
Similar changes in parrot and human genomes suggest convergent evolution of cognition
Summary
Parrots are one of the most distinct and intriguing groups of birds, with highly expanded brains, highly developed cognitive and vocal communication skills, and a long lifespan compared to other similar-sized birds. Yet the genetic basis of these traits remains largely unidentified. To address this question, we have generated a high-coverage, annotated assembly of the genome of the blue-fronted Amazon (Amazona aestiva) and carried out extensive comparative analyses with 30 other avian species, including 4 additional parrots. We identified several genomic features unique to parrots, including parrot-specific novel genes and parrot-specific modifications to coding and regulatory sequences of existing genes. We also discovered genomic features under strong selection in parrots and other long-lived birds, including genes previously associated with lifespan determination as well as several hundred new candidate genes. These genes support a range of cellular functions, including telomerase activity; DNA damage repair; control of cell proliferation, cancer, and immunity; and anti-oxidative mechanisms. We also identified brain-expressed, parrot-specific paralogs with known functions in neural development or vocal-learning brain circuits. Intriguingly, parrot-specific changes in conserved regulatory sequences were overwhelmingly associated with genes that are linked to cognitive abilities and have undergone similar selection in the human lineage, suggesting convergent evolution. These findings bring novel insights into the genetics and evolution of longevity and cognition, as well as provide novel targets for exploring the mechanistic basis of these traits.
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Emanuel Tschopp & Paul Upchurch (2018)
The challenges and potential utility of phenotypic specimen-level phylogeny based on maximum parsimony.
Earth and Environmental Science Transactions of The Royal Society of Edinburgh (advance online publication)
Specimen-level phylogenetic approaches are widely used in molecular biology for taxonomic and systematic purposes. However, they have been largely ignored in analyses based on morphological traits, where phylogeneticists mostly resort to species-level analyses. Recently, a number of specimen-level studies have been published in vertebrate palaeontology. These studies indicate that specimen-level phylogeny may be a very useful tool for systematic reassessments at low taxonomic levels. Herein, we review the challenges when working with individual organisms as operational taxonomic units in a palaeontological context, and propose guidelines of how best to perform a specimen-level phylogenetic analysis using the maximum parsimony criterion. Given that no single methodology appears to be perfectly suited to resolve relationships among individuals, and that different taxa probably require different approaches to assess their systematics, we advocate the use of a number of methodologies. In particular, we recommend the inclusion of as many specimens and characters as feasible, and the analysis of relationships using an extended implied weighting approach with different downweighting functions. Resulting polytomies should be explored using a posteriori pruning of unstable specimens, and conflicting tree topologies between different iterations of the analysis should be evaluated by a combination of support values such as jackknifing and symmetric resampling. Species delimitation should be consistent among the ingroup and based on a reproducible approach. Although time-consuming and methodologically challenging, specimen-level phylogenetic analysis is a highly useful tool to assess intraspecific variability and provide the basis for a more informed and accurate creation of species-level operational taxonomic units in large-scale systematic studies. It also has the potential to inform us about past speciation processes, morphological trait evolution, and their potential intrinsic and extrinsic drivers in pre-eminent detail.
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