Three new naraoiid species from the Burgess Shale,with a morphometric and phylogenetic reinvestigation of Naraoiidae

Naraoiids are non‐biomineralized euarthropods characterized by the complete fusion of post‐cephalic tergo‐pleurae into a single shield, as well as an extensively ramified digestive tract. Ranging from the early Cambrian to the late Silurian (Pridoli), these arthropods of simple appearance have traditionally been associated with the early diversification of trilobites and their close relatives, but the interrelationships and affinities of naraoiids within Artiopoda remain poorly characterized. Three new species from the Burgess Shale (middle Cambrian, Stage 5) of British Columbia, Canada, are described here: Misszhouia canadensis sp. nov., from Marble Canyon (Kootenay National Park), the first species belonging to the genus Misszhouia outside of China; Naraoia magna sp. nov., from Marble Canyon and also from the Raymond Quarry (Yoho National Park), the largest species of Naraoia described thus far, reaching up to 9 cm in length; and Naraoia arcana sp. nov., from two sublocalities on Mount Stephen (Yoho National Park), defined by its unusual combination of spines. This new material shows that gut morphology is no longer a reliable character to distinguish Misszhouia from Naraoia. We demonstrate that Naraoia and Misszhouia can instead be discriminated morphometrically, based on simple metrics of the dorsal exoskeleton. Our quantitative results also help with inter‐specific discrimination and illustrate possible cases of sexual dimorphism. Phylogenetically, the inclusion of morphometric data adds resolution to our cladogram, although parsimony and likelihood treatments provide somewhat different evolutionary scenarios. In all cases, liwiines are nested within Naraoiidae, resolved as the most derived clade of trilobitomorph arthropods.     

山东潍坊寒武系苗岭统乌溜阶馒头组上部的腕足动物

寒武系腕足动物属种多样性高、个体数量丰富、形态差异明显、地理分布广泛,具有辅助寒武系三叶虫生物地层划分和对比的潜力.华北板块寒武系苗岭统沉积和化石记录发育良好,是中国苗岭统的经典研究区之一.前人己针对华北寒武系苗岭统乌溜阶腕足动物的系统古生物学开展了一系列基础工作,但这些相关研究主要集中于辽宁地区,目前对华北其他地区苗...     

First decapod crustaceans in a Late Devonian continental ecosystem

The origin and early diversification of decapod crustaceans and their expansion from marine to continental environments are key events in arthropod evolution. Rare fossil decapods are known from the Palaeozoic, and the earliest eumalacostracans with undoubted decapod affinities are the Late Devonian Palaeopalaemon and Aciculopoda, found in offshore marine deposits. Here, we describe a new species of the shrimp Tealliocaris found in floodplain and temporary pond deposits from the Famennian (Late Devonian) of Belgium, together with a rare Palaeozoic assemblage of other crustaceans (conchostracans, notostracans and anostracans) and chelicerates (eurypterids). Tealliocaris walloniensis sp. nov. documents the earliest occurrence of continental decapod crustaceans and indicates that decapods have been part of continental ecosystems at least since the Late Devonian.     

Importance of metapopulation dynamics to explain fish persistence in a river system

1. Habitat modification and fragmentation are key factors responsible for fish population decline worldwide. Previous assessments documented a total of 72 species extinctions for the sole class of Actinopterygii. However, global extinctions are difficult to monitor or study based on fossil records. By contrast, local extinctions occurring at the population level are easier to study. Given this context, an important question relates to whether extinction dynamics studied at the local scale can provide useful information to understand extinctions occurring at larger scales. This would be the case if local extinctions were not balanced by recolonisation as in a classic metapopulation. Our aim is thus to explain the observed regional (per basin) persistence of 252 fish populations by testing contribution of local extinction rates and more generally metapopulation dynamics components.
2. To address this aim, we used the annual extinction probability of 252 regional populations of up to 14 species inhabiting 18 coastal rivers, which became isolated c. 8,500 years ago. We specifically compared extinction probabilities obtained by seven theoretical models to investigate whether regional extinction rates (i.e. loss from a river system) were correlated to local extinction rates (i.e. loss from an occupied site) and the role of metapopulation dynamics to explain regional persistence.
3. Using empirical data, we showed the importance of variables related to metapopulation dynamics to explain extinction rates across the 18 river systems. As expected, the regional extinction rate decreased with the colonisation rate, area, metapopulation size, and percentage of occupied localities. By contrast, an inconsistent relationship emerged between regional and local extinction rates, as species with high local extinction rates were not particularly prone to regional extinction.
4. Our results provide strong support for the contribution of colonisation rates to explain persistence. Overall, our results show that the equilibrium number of occupied localities could be a good predictor of the long-term persistence of metapopulations in rivers. Finally, our results suggest the importance of connectivity to maintain sustainable populations within the river system.

     

On the extinction of the Dune Shearwater (Puffinus holeae) from the Canary Islands

Insular ecosystems have been subjected to severe hardship during the last millennia. Large numbers of insular bird species have undergone local disappearances and full extinctions, and a high number of insular birds are currently categorised as endangered species. In most of these cases, extinction—or endangerment—is in direct relation to the arrival of ‘aboriginal’ and/or imperialist waves of human settlement. Insular bird extinction events have been documented to have occurred at times corresponding to aboriginal settlement at many archipelagos and isolated islands, such as the Hawaiian Islands, New Zealand, the West Indies or the tropical Pacific Islands. However, no bird extinctions could be attributed to the first settlers of the Canary Islands—until now. The first accelerator mass spectrometer radiocarbon (¹⁴C) dating of collagen from a bone of the Dune Shearwater Puffinus holeae (3395 ± 30 year BP), an extinct bird from the Canary Islands, indicates a late Holocene extinction event. This relatively recent date, together with some features of this bird (large body size, breeding areas situated at very accessible places) and the absence of its bones from the entire archaeological record suggests that the extinction occurred close to the time that the first human settlement occurred on the islands.     

Lithostratigraphy of the Lower Cambrian metaclastics and their age based on trace fossils in the Sand?kl? region, southwestern Turkey

In the Sand?kl? region of the Taurus Range of Turkey, greater than 3000 m in thickness metamorphosed siliciclastics and volcanics (Kocayayla Group) underlies the trilobite-and conodont-bearing Middle-Late Cambrian Hudai Quartzite and Çaltepe Formation.The Kocayayla Group, previously regarded as Infracambrian or Precambrian, is dated for the first time as Early Cambrian on the basis of trace fossils. Cruziana ?fasciculata, C. ?salomonis, ?Cruziana isp., ?Diplichnites isp., Monomorphichnus isp., Petalichnus isp., Rusophycus ?avalonensis, R. ?latus, Arenicolites isp., cf. Altichnus foeyni, Planolites isp., Skolithos isp., and ?Treptichnus isp. have been recognised. These trace fossils are considered Tommotian or younger in age but older than the overlying, trilobite and conodont bearing Middle Cambrian limestones of the Çaltepe Formation. The trace fossils were likely produced by trilobites, suspension feeding annelids and deposit feeding “worms”, probably polychaetes. Sections bearing abundant Skolithos represent the Skolithos ichnofacies, which is typical of high energy environments with loose sandy, well sorted to slightly muddy substrates in intertidal to shallow subtidal zones. The other trace fossils represent the Cruziana ichnofacies, which is typical of subtidal, poorly sorted and soft substrates, from moderate energy to low energy environments between the fairweather and storm wave base.The Kocayayla Group was deposited at an early stage in a shallow marine stable shelf condition. The shelf subsided in a later stage and was affected by normal faults along which mafic and felsic volcanic rocks erupted. The volcanic activity had ceased and a shallow marine clastic sedimentation took place in the final stage of the shelf development. The Kocayayla Group was deformed and metamorphosed before the deposition of the trilobite-bearing Middle-Upper Cambrian succession.     

山东寒武系苗岭统三叶虫消化系统的化石证据

三叶虫是寒武纪演化动物群中最引人注目的成员之一,其内部解剖结构一直以来受到广泛关注.与其他非生物矿化软体结构相比,三叶虫的消化系统更容易留下化石记录,为探索其内部结构提供了难得的机会.本文描述了来自山东省潍坊市寒武系馒头组的Proasaphiscus,Lioparia,Deiradonyx和Iranoleesia,以及...     

Biotic effects of the Chicxulub impact,K–T catastrophe and sea level change in Texas

Biotic effects of the Chicxulub impact, the K–T event and sea level change upon planktic foraminifera were evaluated in a new core and outcrops along the Brazos River, Texas, about 1000 km from the Chicxulub impact crater on Yucatan, Mexico. Sediment deposition occurred in a middle neritic environment that shallowed to inner neritic depths near the end of the Maastrichtian. The sea level fall scoured submarine channels, which were infilled by a sandstone complex with reworked Chicxulub impact spherules and clasts with spherules near the base. The original Chicxulub impact ejecta layer was discovered 45–60 cm below the sandstone complex, and predates the K–T mass extinction by about 300,000 years.Results show that the Chicxulub impact caused no species extinctions or any other significant biotic effects. The subsequent sea level fall to inner neritic depth resulted in the disappearance of all larger (> 150 μm) deeper dwelling species creating a pseudo-mass extinction and a survivor assemblage of small surface dwellers and low oxygen tolerant taxa. The K–T boundary and mass extinction was identified 40–80 cm above the sandstone complex where all but some heterohelicids, hedbergellids and the disaster opportunistic guembelitrids went extinct, coincident with the evolution of first Danian species and the global δ¹³C shift. These data reveal that sea level changes profoundly influenced marine assemblages in near shore environments, that the Chicxulub impact and K–T mass extinction are two separate and unrelated events, and that the biotic effects of this impact have been vastly overestimated.     

Planktonic foraminiferal turnover, diversity fluctuations and geochemical signals across the Eocene/Oligocene boundary in Tanzania

A major turnover in planktonic foraminifera occurred across the Eocene/Oligocene (E/O) boundary. New drill holes through the E/O boundary in southern Tanzania contain extremely well-preserved and diverse assemblages of planktonic foraminifera. Here we document a 1.2 million year record of assemblages, diversity and stable isotope fluctuations through this critical interval, which is often dissolved and/or recrystallised in carbonate-rich facies. The E/O boundary is marked by the abrupt extinction of all five remaining species of the family Hantkeninidae and a distinct size reduction in the genus Pseudohastigerina. The boundary is preceded over a short stratigraphic interval by the extinction of Turborotalia cerroazulensis, Turborotalia cocoaensis and Turborotalia cunialensis. Quantitative analysis of planktonic foraminiferal assemblages reveals significant changes in the abundance of certain species and the composition of the assemblages. We compare diversity fluctuations to the stable isotope record of Pseudohastigerina naguewichiensis and use multispecies stable isotope analyses to determine the life habitats of the most important species. A major shift in the evenness occurs at ~ 33.8 Ma associated with the extinction of the T cerroazulensis group suggesting acute ecological disturbance. We propose that the extinction of the T. cerroazulensis group at ~ 33.8 Ma was directly related to cooling of sea surface temperatures, while the extinction of Hantkeninidae was due to modifications in the thermal structure of the oceans and associated productivity changes. After the extinctions, renewed origination and diversification occurred, leading to a characteristic Oligocene planktonic foraminifer assemblage.     

Innovation not recovery: dynamic redox promotes metazoan radiations

Environmental fluctuations in redox may reinforce rather than hinder evolutionary transitions, such that variability in near‐surface oceanic oxygenation can promote morphological evolution and novelty. Modern, low‐oxygen regions are heterogeneous and dynamic habitats that support low diversity and are inhabited by opportunistic and non‐skeletal metazoans. We note that several major radiation episodes follow protracted or repeating intervals (>1 million years) of persistent and dynamic shallow marine redox (oceanic anoxic events). These are also often associated with short‐lived mass‐extinction events (<0.5 million years) where skeletal benthic incumbents are removed, and surviving or newly evolved benthos initially inhabit transient oxic habitats. We argue that such intervals create critical opportunities for the generation of evolutionary novelty, followed by innovation and diversification. We develop a general model for redox controls on the distribution and structure of the shallow marine benthos in a dominantly anoxic world, and compile data from the terminal Ediacaran–mid‐Cambrian (∼560–509 Ma), late Cambrian–Ordovician (∼500–445 Ma), and Permo‐Triassic (∼255–205 Ma) to test these predictions. Assembly of phylogenetic data shows that prolonged and widespread anoxic intervals indeed promoted morphological novelty in soft‐bodied benthos, providing the ancestral stock for subsequently skeletonized lineages to appear as innovations once oxic conditions became widespread and stable, in turn promoting major evolutionary diversification. As a result, we propose that so‐called ‘recovery’ intervals after mass extinctions might be better considered as ‘innovation’ intervals.     

Re-assessing current extinction rates

There is a widespread belief that we are experiencing a mass extinction event similar in severity to previous mass extinction events in the last 600 million years where up to 95% of species disappeared. This paper reviews evidence for current extinctions and different methods of assessing extinction rates including species–area relationships and loss of tropical forests, changing threat status of species, co-extinction rates and modelling the impact of climate change. For 30 years some have suggested that extinctions through tropical forest loss are occurring at a rate of up to 100 species a day and yet less than 1,200 extinctions have been recorded in the last 400 years. Reasons for low number of identified global extinctions are suggested here and include success in protecting many endangered species, poor monitoring of most of the rest of species and their level of threat, extinction debt where forests have been lost but species still survive, that regrowth forests may be important in retaining ‘old growth’ species, fewer co-extinctions of species than expected, and large differences in the vulnerability of different taxa to extinction threats. More recently, others have suggested similar rates of extinction to earlier estimates but with the key cause of extinction being climate change, and in particular rising temperatures, rather than deforestation alone. Here I suggest that climate change, rather than deforestation is likely to bring about such high levels of extinction since the impacts of climate change are local to global and that climate change is acting synergistically with a range of other threats to biodiversity including deforestation.     

Local extinctions and recolonisations of passerine bird populations in small woods

This paper considers, for eight species of woodland bird, the factors that influenced both local extinctions and recolonisations in 145 woods over 3 years. In all species, probability of local extinction was inversely related to population size; most local extinctions occurred in woods containing one to three breeding pairs. However, considerable variation in extinction probabilities occurred between species and between years. In addition, the suitability of habitat within a wood (more extinctions in less suitable woods) was important for wren Troglodytes troglodytes, song thrush Turdus philomelos and blue tit Parus caeruleus; also, the structure of the surrounding landscape was important for blue tit, great tit Parus major, and chaffinch Fringilla coelebs (more extinctions in localities with less woodland). In only two species was the probability of recolonisation related to any of the measured variables. Wrens were more likely to recolonise larger woods, whereas song thrushes were more likely to recolonise woods with a high habitat suitability rating and those which are more isolated from other woodland     

A theoretical quantitative genetic study of negative ecological interactions and extinction times in changing environments

Background  

Rapid human-induced changes in the environment at local, regional and global scales appear to be contributing to population declines and extinctions, resulting in an unprecedented biodiversity crisis. Although in the short term populations can respond ecologically to environmental alterations, in the face of persistent change populations must evolve or become extinct. Existing models of evolution and extinction in changing environments focus only on single species, even though the dynamics of extinction almost certainly depend upon the nature of species interactions.     

Mitogenomic phylogeny of Nassarius (Gastropoda: Neogastropoda)

Nassariids (Family Nassariidae) are a group of marine snails that are distributed worldwide, with their maximum species diversity in tropical regions, particularly the Indo‐Pacific. However, the traditional taxonomy of Nassariidae defined by shell or radula characters is usually inconsistent with little phylogenetic signal. In the present study, the complete mitochondrial (mt) genomes of nine Nassarius species were sequenced and compared with other eight nassariid species previously reported. All nassariid mt genomes showed the same gene order as in most caenogastropods and shared a very similar pattern with respect to genome size, nucleotide composition and AT contents. A deletion of three nucleotides in nad6 gene was detected in Nassarius jacksonianus and Nassarius acuticostus, and this feature also provided implications for nassariid phylogeny. The genetic distance analysis and reconstructed phylogeny revealed a distant relationship between N. jacksonianus or N. acuticostus and other members in Nassarius. The mitogenomic phylogeny recovered the evolutionary relationships within Nassarius with high statistical support. In addition, a chronogram was reconstructed under an uncorrelated relaxed molecular clock, which dated the divergence among main lineages of Nassarius during ~31 MYA.     

Stepwise mass extinctions and impact events: Late Eocene to early Oligocene

Species ranges and relative abundances of dominant planktonic foraminifers of eight late Eocene to early Oligocene deep-sea sections are discussed to determine the nature and magnitude of extinctions and to investigate a possible cause-effect relationship between impact events and mass extinctions.Late Eocene extinctions are neither catastrophic nor mass extinctions, but occur stepwise over a period of about 1–2 million years. Four stepwise extinctions are identified at the middle/late Eocene boundary, the upperGlobigerapsis semiinvoluta zone, theG. semiinvoluta/Globorotalia cerroazulensis zone boundary and at the Eocene/Oligocene boundary. Each stepwise extinction event represents a time of accelerated faunal turnover characterized by generally less than 15% species extinct and in itself is not a significant extinction event. Relative species abundance changes at each stepwise extinction event, however, indicate a turnover involving > 60% of the population implying major environmental changes.There microtektite horizons are present in late Eocene sediments; one in the upperG. semiinvoluta zone (38.2 Ma) and two closely spaced layers only a few thousand years apart in the lower part of theGloborotalia cerroazulensis zone (37.2 Ma). Each of the three impact events appears to have had some effect on microplankton communities. However, the overriding factor that led to the stepwise mass extinctions may have been the result of multiple causes as there is no evidence of impacts associated with the step preceding, or the step following the deposition of the presently known microtektite horizons.     

Length–weight and length–length relationships of 11 fish species from the Sea of Okhotsk

Estimated length–weight relationships are presented for 11 marine fish species representing six families, found above the continental shelf and in the pelagial of the Okhotsk Sea. A total of 13,841 specimens were caught by trawls that were equipped with a 1.0 by 1.2 cm mesh webbing inset. The period between 1974 and 2015 comprised mostly spring and autumn months. All length–weight relationships were highly significant (r² ≥ .95) on a log scale. None of the species had previous length–weight estimates, and two species had no previous length–length estimates in the FishBase.     

Body length of bony fishes was not a selective factor during the biggest mass extinction of all time

The Permo‐Triassic mass extinction devastated life on land and in the sea, but it is not clear why some species survived and others went extinct. One explanation is that lineage loss during mass extinctions is a random process in which luck determines which species survive. Alternatively, a phylogenetic signal in extinction may indicate a selection process operating on phenotypic traits. Large body size has often emerged as an extinction risk factor in studies of modern extinction risk, but this is not so commonly the case for mass extinctions in deep time. Here, we explore the evolution of non‐teleostean Actinopterygii (bony fishes) from the Devonian to the present day, and we concentrate on the Permo‐Triassic mass extinction. We apply a variety of time‐scaling metrics to date the phylogeny, and show that diversity peaked in the latest Permian and declined severely during the Early Triassic. In line with previous evidence, we find the phylogenetic signal of extinction increases across the mass extinction boundary: extinction of species in the earliest Triassic is more clustered across phylogeny compared to the more randomly distributed extinction signal in the late Permian. However, body length plays no role in differential survival or extinction of taxa across the boundary. In the case of fishes, size did not determine which species survived and which went extinct, but phylogenetic signal indicates that the mass extinction was not a random field of bullets.     

埃迪卡拉纪至寒武纪苗岭世刺细胞动物化石研究现状与展望

刺细胞动物是一类具有刺细胞的水生无脊椎动物,分布在世界各地的海洋和淡水中.作为后生动物最早分化出的一支,刺细胞动物对研究后生动物的起源和早期演化具有极其重要的意义,也为研究后生动物系统发育、地层对比和古地理恢复等方面提供了重要的科研线索.本文简要介绍了刺细胞动物早期(埃迪卡拉纪至寒武纪苗岭世)的化石记录和研究现状,将刺...     

Human‐mediated extirpation of the unique Chatham Islands sea lion and implications for the conservation management of remaining New Zealand sea lion populations

While terrestrial megafaunal extinctions have been well characterized worldwide, our understanding of declines in marine megafauna remains limited. Here, we use ancient DNA analyses of prehistoric (<1450–1650 AD) sea lion specimens from New Zealand's isolated Chatham Islands to assess the demographic impacts of human settlement. These data suggest there was a large population of sea lions, unique to the Chatham Islands, at the time of Polynesian settlement. This distinct mitochondrial lineage became rapidly extinct within 200 years due to overhunting, paralleling the extirpation of a similarly large endemic mainland population. Whole mitogenomic analyses confirm substantial intraspecific diversity among prehistoric lineages. Demographic models suggest that even low harvest rates would likely have driven rapid extinction of these lineages. This study indicates that surviving Phocarctos populations are remnants of a once diverse and widespread sea lion assemblage, highlighting dramatic human impacts on endemic marine biodiversity. Our findings also suggest that Phocarctos bycatch in commercial fisheries may contribute to the ongoing population decline.