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Mass Extinction (mass + extinction)
Kinds of Mass Extinction Terms modified by Mass Extinction Selected AbstractsTHE END-PERMIAN MASS EXTINCTION WAS SYNCHRONOUS COINCIDED WITH THE EVOLUTION OF TOXIC ALGAEJOURNAL OF PHYCOLOGY, Issue 2001Article first published online: 24 SEP 200 Lee, R. E.1 & Kugrens, P.2 1Department of Biomedical Sciences, College of Veterinary Medicine, Colorado State University, Fort Collins, CO 80523; 2Department of Biology, Colorado State University, Fort Collins, Co 80523 USA The cause of the end-Permian mass extinction, the greatest of all mass extinctions, is one of the most intriguing mysteries in the history of life. The end-Permian mass extinction was primarily a marine event, resulting principally in the elimination of sessile filter-feeding organisms. Based on two methods, molecular clocks and correlation with ancient atmospheric CO2, the algae derived from secondary endosymbioses are believed to have originated in the middle to late Permian. All of the toxic marine algae in today's oceans are derived from secondary endosymbioses. Therefore it appears likely that the end-Permian extinction was due to the evolution of toxic algae in the phytoplankton of late-Permian seas. Sieving of the toxic algae in the phytoplankton likely resulted in the decline and eventual elimination of a large portion of the Paleozoic fauna during the end-Permian mass extinction. [source] The Father of All Mass ExtinctionsCONSERVATION, Issue 3 2004There is a good possibility that losses in diversity in the present will surpass anything in the geological past. First page of article [source] History of marine biodiversityGEOLOGICAL JOURNAL, Issue 3-4 2001Peter M. Sheehan Abstract During the Phanerozoic, three steps of increasing diversity each had a unique Evolutionary Fauna (EF). During each EF, there were geologically long intervals of community stasis referred to as Ecological Evolutionary Units (EEUs). These intervals were characterized by communities composed of incumbent faunas that dominated particular habitats. Niches that were already occupied by incumbents were seldom invaded by new taxa, and the resilience of the incumbents to new competitors resulted in the long interval stasis. Most EEUs were terminated by extinction events that were caused by severe disruptions of the physical environment such as glaciations and extraterrestrial impacts. During mass extinctions many niches were vacated when incumbents were eliminated. Mass extinctions were followed by recovery intervals lasting on the order of 5 million years during which many surviving clades evolved adaptations which allowed them to move into vacated niches. New incumbents were established during these recovery intervals, and the next EEU began. In many ways, the recovery intervals resemble times when organisms invaded previously unoccupied ecospace, such as the emergence of life on land or the progressive filling of previously unoccupied habitats such as deep-burrowing and high epifaunal tiers that were colonized during the Palaeozoic. The recognition of long intervals of ecological stasis and the importance of physical disruptions in clearing incumbents is forcing revision of the traditional evolutionary viewpoint. The idea that most evolutionary change was accomplished very gradually by competition between organisms and by becoming better adapted to a relatively stable environment is being replaced by a recognition that major morphological and synecological changes tend to occur very rapidly and at times when there are few established competitors. Copyright © 2001 John Wiley & Sons, Ltd. [source] Metapopulation Extinction Risk under Spatially Autocorrelated DisturbanceCONSERVATION BIOLOGY, Issue 2 2005A. S. KALLIMANIS patrón espacial de perturbación; simulaciones espacialmente explícitas; SLOSS; umbral de extinción Abstract:,Recent extinction models generally show that spatial aggregation of habitat reduces overall extinction risk because sites emptied by local extinction are more rapidly recolonized. We extended such an investigation to include spatial structure in the disturbance regime. A spatially explicit metapopulation model was developed with a wide range of dispersal distances. The degree of aggregation of both habitat and disturbance pattern could be varied from a random distribution, through the intermediate case of a fractal distribution, all the way to complete aggregation (single block). Increasing spatial aggregation of disturbance generally increased extinction risk. The relative risk faced by populations in different landscapes varied greatly, depending on the disturbance regime. With random disturbance, the spatial aggregation of habitat reduced extinction risk, as in earlier studies. Where disturbance was spatially autocorrelated, however, this advantage was eliminated or reversed because populations in aggregated habitats are at risk of mass extinction from coarse-scale disturbance events. The effects of spatial patterns on extinction risk tended to be reduced by long-distance dispersal. Given the high levels of spatial correlation in natural and anthropogenic disturbance processes, population vulnerability may be greatly underestimated both by classical (nonspatial) models and by those that consider spatial structure in habitat alone. Resumen:,Los modelos recientes de extinción generalmente muestran que la agregación espacial de hábitat reduce el riesgo de extinción debido a una recolonización más rápida de sitios vacíos por extinción local. Extendimos la investigación para incluir la estructura espacial en el régimen de perturbación. Desarrollamos un modelo metapoblacional espacialmente explícito en el que el patrón espacial tanto del hábitat como de los regímenes de perturbación podía variar aleatoriamente de fractal a completamente agregado (bloque) y con una amplia gama de distancias de dispersión. El incremento de la agregación espacial de la perturbación generalmente incrementó el riesgo de extinción. El riesgo relativo que enfrentan poblaciones en paisajes diferentes fue muy variable, dependiendo del régimen de perturbación. Con perturbación aleatoria, la agregación espacial de hábitat redujo el riesgo de extinción, como en estudios anteriores. Sin embargo, cuando la perturbación estaba autocorrelacionada espacialmente, esta ventaja se eliminaba o invertía debido a que las poblaciones en hábitats agregados están en riesgo de extinción masiva por eventos perturbadores a escala gruesa. Los efectos de patrones espaciales sobre el riesgo de extinción tendieron a reducirse por la dispersión de larga distancia. Debido a los altos niveles de correlación espacial en los procesos naturales y humanos de perturbación, la vulnerabilidad puede estar enormemente subestimada tanto por modelos clásicos (no espaciales) como por los que sólo consideran la estructura espacial del habitat. Los modelos que consideran la estructura espacial del hábitat solo subestiman el riesgo en comparación con modelos que consideran la estructura especial de la perturbación. [source] The fate of the homoctenids (Tentaculitoidea) during the Frasnian,Famennian mass extinction (Late Devonian)GEOBIOLOGY, Issue 3 2006DAVID BONDArticle first published online: 18 AUG 200 ABSTRACT The homoctenids (Tentaculitoidea) are small, conical-shelled marine animals that are among the most abundant and widespread of all Late Devonian fossils. They were a principal casualty of the Frasnian,Famennian (F-F, Late Devonian) mass extinction, and thus provide an insight into the extinction dynamics. Despite their abundance during the Late Devonian, they have been largely neglected by extinction studies. A number of Frasnian,Famennian boundary sections have been studied, in Poland, Germany, France, and the USA. These sections have yielded homoctenids, which allow precise recognition of the timing of the mass extinction. It is clear that the homoctenids almost disappear from the fossil record during the latest Frasnian ,Upper Kellwasser Event'. The coincident extinction of this pelagic group, and the widespread development of intense marine anoxia within the water column, provides a causal link between anoxia and the F-F extinction. Most notable is the sudden demise of a group, which had been present in rock-forming densities, during this anoxic event. One new species, belonging to Homoctenus is described, but is not formally named here. [source] Body size evolution in Mesozoic birds: little evidence for Cope's ruleJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2008R. J. BUTLER Abstract Cope's rule, the tendency towards evolutionary increases in body size, is a long-standing macroevolutionary generalization that has the potential to provide insights into directionality in evolution; however, both the definition and identification of Cope's rule are controversial and problematic. A recent study [J. Evol. Biol. 21 (2008) 618] examined body size evolution in Mesozoic birds, and claimed to have identified evidence of Cope's rule occurring as a result of among-lineage species sorting. We here reassess the results of this study, and additionally carry out novel analyses testing for within-lineage patterns in body size evolution in Mesozoic birds. We demonstrate that the nonphylogenetic methods used by this previous study cannot distinguish between among- and within-lineage processes, and that statistical support for their results and conclusions is extremely weak. Our ancestor,descendant within-lineage analyses explicitly incorporate recent phylogenetic hypotheses and find little compelling evidence for Cope's rule. Cope's rule is not supported in Mesozoic birds by the available data, and body size evolution currently provides no insights into avian survivorship through the Cretaceous,Paleogene mass extinction. [source] THE END-PERMIAN MASS EXTINCTION WAS SYNCHRONOUS COINCIDED WITH THE EVOLUTION OF TOXIC ALGAEJOURNAL OF PHYCOLOGY, Issue 2001Article first published online: 24 SEP 200 Lee, R. E.1 & Kugrens, P.2 1Department of Biomedical Sciences, College of Veterinary Medicine, Colorado State University, Fort Collins, CO 80523; 2Department of Biology, Colorado State University, Fort Collins, Co 80523 USA The cause of the end-Permian mass extinction, the greatest of all mass extinctions, is one of the most intriguing mysteries in the history of life. The end-Permian mass extinction was primarily a marine event, resulting principally in the elimination of sessile filter-feeding organisms. Based on two methods, molecular clocks and correlation with ancient atmospheric CO2, the algae derived from secondary endosymbioses are believed to have originated in the middle to late Permian. All of the toxic marine algae in today's oceans are derived from secondary endosymbioses. Therefore it appears likely that the end-Permian extinction was due to the evolution of toxic algae in the phytoplankton of late-Permian seas. Sieving of the toxic algae in the phytoplankton likely resulted in the decline and eventual elimination of a large portion of the Paleozoic fauna during the end-Permian mass extinction. [source] Complex behavioural pattern as an aid to identify the producer of Zoophycos from the Middle Permian of OmanLETHAIA, Issue 2 2009DIRK KNAUST The trace fossil Zoophycos is abundant in transgressive, shallow marine carbonates in the Middle Permian (Wordian) Khuff Formation of the Huqf-Haushi Uplift of Interior Oman. It often occurs as part of a complex (compound) trace fossil that comprises two integrated elements: (i) irregular galleries with straight to gently curved tunnels and interconnected shafts, and (ii) simple planar to complex spreiten structures with a marginal tube (Zoophycos). The galleries are characterized by irregularly winding, dichotomous branching, large variation in shape and size and circular to elliptical vertical cross-sections. Zoophycos consists of spreiten with a marginal tube, either originating as a simple lobe from the convex segment of a curved tunnel, or forming more complex, subcircular, spreiten systems parallel to bedding. The spreiten were formed by simple strip mining, where the animal defecated without producing faecal pellets. U-shaped marginal tubes indicate that the burrows were well aerated. The complex trace fossil points to combined dwelling and deposit-feeding behaviour, with irregular galleries in the firm substrate and Zoophycos spreiten in the softground below it. It can be assumed that the animal used the open tunnel system mainly for dwelling (domichnion) and possibly suspension feeding, but occasionally changed to deposit feeding while creating the spreiten (fodinichnion). The integration of the irregular galleries (tunnels and interconnected shafts) with the marginal tubes of Zoophycos suggests the same producer for this compound trace fossil. Many modern polychaetes produce very similar galleries within firm and soft substrates, and polychaetes are therefore interpreted as the most likely producers. Similarities between Permian and Triassic Zoophycos suggest comparable trace making behaviour before and after the end-Permian mass extinction. [source] Lystrosaurus species composition across the Permo,Triassic boundary in the Karoo Basin of South AfricaLETHAIA, Issue 2 2007JENNIFER BOTHA Lystrosaurus is one of the few therapsid genera that survived the end-Permian mass extinction, and the only genus to have done so in abundance. This study identifies which species of Lystrosaurus have been recovered from Permian and Triassic strata to determine changes in the species composition across the Permo,Triassic (P,T) boundary in the Karoo Basin of South Africa. Data generated from museum collections and recent fieldwork were used to stratigraphically arrange a total of 189 Lystrosaurus specimens to determine which species survived the extinction event. Results reveal that L. curvatus and L. maccaigi lived together on the Karoo floodplains immediately before the extinction event. L. maccaigi did not survive into the Triassic in South Africa. L. curvatus survived, but did not flourish and soon became extinct. Two new species of Lystrosaurus, L. murrayi and L. declivis, appeared in the Early Triassic. It is possible that L. murrayi and L. declivis occupied different niches to L. maccaigi and L. curvatus, and had special adaptations that were advantageous in an Early Triassic environment. We suggest that L. maccaigi may be used as a biostratigraphic marker to indicate latest Permian strata in South Africa and that, in support of previous proposals, the genus Lystrosaurus should not be used as a sole indicator of Triassic-aged strata. Our field data also show that L. curvatus may be regarded as a biostratigraphic indicator of the P,T boundary interval. [source] End-Permian mass extinction: oceanographic consequences of double catastrophic volcanismLETHAIA, Issue 3 2003GRZEGORZ RACKI No abstract is available for this article. [source] MACROEVOLUTION AND MACROECOLOGY THROUGH DEEP TIMEPALAEONTOLOGY, Issue 1 2007NICHOLAS J. BUTTERFIELD Abstract:, The fossil record documents two mutually exclusive macroevolutionary modes separated by the transitional Ediacaran Period. Despite the early appearance of crown eukaryotes and an at least partially oxygenated atmosphere, the pre-Ediacaran biosphere was populated almost exclusively by microscopic organisms exhibiting low diversity, no biogeographical partitioning and profound morphological/evolutionary stasis. By contrast, the post-Ediacaran biosphere is characterized by large diverse organisms, bioprovinciality and conspicuously dynamic macroevolution. The difference can be understood in terms of the unique escalatory coevolution accompanying the early Ediacaran introduction of eumetazoans, followed by their early Cambrian (Tommotian) expansion into the pelagic realm. Eumetazoans reinvented the rules of macroecology through their invention of multitrophic food webs, large body size, life-history trade-offs, ecological succession, biogeography, major increases in standing biomass, eukaryote-dominated phytoplankton and the potential for mass extinction. Both the pre-Ediacaran and the post-Ediacaran biospheres were inherently stable, but the former derived from the simplicity of superabundant microbes exposed to essentially static, physical environments, whereas the latter is based on eumetazoan-induced diversity and dynamic, biological environments. The c. 100-myr Ediacaran transition (extending to the base of the Tommotian) can be defined on evolutionary criteria, and might usefully be incorporated into the Phanerozoic. [source] First Late Triassic Record of a Paleoentomofauna from South America (Malargüe Basin, Mendoza Province, Argentina)ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 4 2010Carsten BRAUCKMANN Abstract: Late Middle Triassic to early Late Triassic insects from Argentina have been previously described from the Bermejo and Cuyana Basins where they have been recovered from the Ischichuca-Los Rastros and Potrerillos-Cacheuta Formations, respectively. The insect fauna discussed herein was collected during field studies in 1986/1987 from the Llantenes section (Norian to Rhaetian? Late Triassic), which is situated in the Malargüe Basin in southern Mendoza province. The insect remains were found in the upper part of the Llantenes section (Llantenes Formation), which is built up of two coarsening-upwards cycles reflecting a deltaic progradation of a fluvial into a lacustrine environment (lower part), succeeded by repeated progradations into a floodplain-dominated environment (upper part; with finds of insects, conchostracans, fish remains, plant fragments, and drifted logs). The new finds represent the youngest Triassic insect records described from Argentina and even from South America in its entirety. There is only one contemporaneous fossil assemblage in Gondwana: in the Clarence/Moreton Basin (Aberdare Conglomerate; Late Norian) in Australia. The new Triassic insects include an impression of an isolated Mecopterida-like wing (Mendozachorista volkheimeri gen. et sp. nov.; Mendozachoristidae fam. nov.), coleopteran elytra of the Permosynidae (Ademosyne rosenfeldi sp. nov. and Ademosyne llantenesensis sp. nov.) and other isolated body fragments. This new Late Triassic entomofauna from Argentina is of considerable importance in the reconstruction of the biotic recovery of continental environments in Gondwana after the catastrophic mass extinction at the P/T boundary. [source] Biodiversity and Sequence of the Middle Triassic Panxian Marine Reptile Fauna, Guizhou Province, ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2009Dayong JIANG Abstract: The Middle Triassic Panxian fauna is a physical marker and representative record of the rapid recovery of the Triassic marine ecosystem following the Early Triassic stagnant stage after the end-Permian mass extinction. Ten marine reptile taxa have been found from the 1.82,2.10 m-thick fossiliferous level in the Upper Member of the Guanling Formation, which can be subdivided into three marine reptile beds through the analysis on the stratigraphic distributions of fossil reptiles. The Lower Reptile Bed yields the sauropterygians Placodus inexpectatus Jiang et al., 2008 and Lariosaurus hongguoensis Jiang et al., 2006, the ichthyopterygians Xinminosaurus catactes Jiang et al., 2008 and Phalarodon cf. Phalarodon fraasi Merriam, 1910, associated with Mixosaurus panxianensis Jiang et al., 2006, representing a stage of predominance of durophagous taxa. In this bed, the large complete skeletons may reach up to 2.3 m in length, and lithofacies and chemostratigraphic analyses indicate a relatively deep carbonate platform with an oxic water environment near the bottom, as well as a rising sea level. The Middle Reptile Bed yields the sauropterygian Nothosaurus yangjuanensis Jiang et al., 2006 and the archosaur Qianosuchus mixtus Li et al., 2006, associated with Mixosaurus panxianensis Jiang et al., 2006. The fossils in this bed are characterized by its pincering dentition and large overall body size, with the largest possibly exceeding 3 m in length. This bed might represent a time of deepest basin with relatively anoxic condition near the bottom. The Upper Reptile Bed yields the sauropterygians Wumengosaurus delicatomandibularis Jiang et al., 2008, Keichousaurus sp., the protorosaur Dinocephalosaurus orientalis Li, 2003, and the ichthyopterygian Mixosaurus panxianensis Jiang et al., 2006. In this bed, reptilian taxa characterized by suction feeding appeared, and most are less than 1 m long. This bed corresponds to a period of decreasing water depth. [source] Habitat Loss and Extinction in the Hotspots of BiodiversityCONSERVATION BIOLOGY, Issue 4 2002Thomas M. Brooks None of these hotspots have more than one-third of their pristine habitat remaining. Historically, they covered 12% of the land's surface, but today their intact habitat covers only 1.4% of the land. As a result of this habitat loss, we expect many of the hotspot endemics to have either become extinct or,because much of the habitat loss is recent,to be threatened with extinction. We used World Conservation Union [ IUCN ] Red Lists to test this expectation. Overall, between one-half and two-thirds of all threatened plants and 57% of all threatened terrestrial vertebrates are hotspot endemics. For birds and mammals, in general, predictions of extinction in the hotspots based on habitat loss match numbers of species independently judged extinct or threatened. In two classes of hotspots the match is not as close. On oceanic islands, habitat loss underestimates extinction because introduced species have driven extinctions beyond those caused by habitat loss on these islands. In large hotspots, conversely, habitat loss overestimates extinction, suggesting scale dependence (this effect is also apparent for plants). For reptiles, amphibians, and plants, many fewer hotspot endemics are considered threatened or extinct than we would expect based on habitat loss. This mismatch is small in temperate hotspots, however, suggesting that many threatened endemic species in the poorly known tropical hotspots have yet to be included on the IUCN Red Lists. We then asked in which hotspots the consequences of further habitat loss (either absolute or given current rates of deforestation) would be most serious. Our results suggest that the Eastern Arc and Coastal Forests of Tanzania-Kenya, Philippines, and Polynesia-Micronesia can least afford to lose more habitat and that, if current deforestation rates continue, the Caribbean, Tropical Andes, Philippines, Mesoamerica, Sundaland, Indo-Burma, Madagascar, and Chocó,Darién,Western Ecuador will lose the most species in the near future. Without urgent conservation intervention, we face mass extinctions in the hotspots. Resumen: Casi la mitad del total de plantas vasculares del mundo y un tercio de los vertebrados terrestres son endémicos en 25 "áreas críticas" para la biodiversidad, cada una de las cuales tiene por lo menos 1500 especies de plantas endémicas. En ninguno de estos sitios permanece más de un tercio de su hábitat prístino. Históricamente, cubrían 12% de la superficie terrestre, pero en la actualidad su hábitat intacto cubre solo 1.4% del terreno. Como resultado de esta pérdida de hábitat esperamos que muchas de las especies endémicas a estos sitios estén extintas o , porque la pérdida de hábitat es reciente , se encuentren amenazadas de extinción. Utilizamos Listas Rojas de UICN para comprobar esta predicción. En general, entre la mitad y dos tercios de las plantas amenazadas y el 57% de los vertebrados terrestres amenazados son endémicos de áreas críticas para la biodiversidad. Para aves y mamíferos en general, las predicciones de extinción en las áreas críticas para la biodiversidad, basadas en la pérdida de hábitat, coinciden con el número de especies consideradas extintas o amenazadas independientemente. En dos clases de áreas críticas para la biodiversidad la coincidencia no es muy grande. En islas oceánicas, la pérdida de hábitat subestima la extinción porque las especies introducidas han causado más extinciones que las producidas por la reducción del hábitat. Por lo contrario, la pérdida de hábitat sobrestima la extinción en áreas críticas para la biodiversidad extensas, lo que sugiere una dependencia de escala (este efecto también es aparente para plantas). Para reptiles, anfibios y plantas mucho menos especies endémicas son consideradas amenazadas o extintas por pérdida de hábitat. Sin embargo, esta discordancia es pequeña en áreas críticas para la biodiversidad en zonas templadas templadas, lo que sugiere que muchas especies endémicas amenazadas en las poco conocidas áreas críticas para la biodiversidad en zonas tropicales aun están por incluirse en las Listas Rojas. Posteriormente nos preguntamos en que áreas críticas para la biodiversidad serían más serias las consecuencias de una mayor pérdida de hábitat (absoluta o con las tasas actuales de deforestación). Nuestros resultados sugieren que el Arco Oriental y los Bosques Costeros de Tanzania/Kenia, Filipinas, Polinesia/Micronesia no pueden soportar mayores pérdidas y que, si continúan las tasas de deforestación actuales, el Caribe, Andes Tropicales, Filipinas, Mesoamérica, Sundaland, Indo-Burma, Madagascar y Chocó/Darién/Ecuador Occidental perderán más especies en el futuro. Sin acciones urgentes de conservación, habrá extinciones masivas en las áreas críticas para la biodiversidad. [source] RESISTANCE OF SPIDERS TO CRETACEOUS-TERTIARY EXTINCTION EVENTSEVOLUTION, Issue 11 2003David Penney Abstract Throughout Earth history a small number of global catastrophic events leading to biotic crises have caused mass extinctions. Here, using a technique that combines taxonomic and numerical data, we consider the effects of the Cenomanian,Turonian and Cretaceous,Tertiary mass extinctions on the terrestrial spider fauna in the light of new fossil data. We provide the first evidence that spiders suffered no decline at the family level during these mass extinction events. On the contrary, we show that they increased in relative numbers through the Cretaceous and beyond the Cretaceous,Tertiary extinction event. [source] High-resolution Lopingian (Late Permian) timescale of South ChinaGEOLOGICAL JOURNAL, Issue 2-3 2010Shu-Zhong Shen Abstract The Lopingian represents the last epoch of the Palaeozoic Era and is bracketed by two severe biotic mass extinctions associated with dramatic environmental changes. The Lopingian Epoch lasted about 7 millions years and was also bracketed by large volcanic eruptions with the Emeishan volcanics at the base and the Siberian traps at the top. Considerable data have accumulated recently and in this paper we attempt to summarize these findings in a high-resolution Lopingian (Late Permian) timescale that integrates currently available multiple biostratigraphic, isotope chemostratigraphic, geochronologic and magnetostratigraphic data. In South China at least 13 conodont zones, multiple polarity zones and large carbon isotope fluctuations in the Lopingian are recognized and provide the high-resolution calibration that is essential to study this Late Permian interval characterized by Earth's largest biotic extinction. We also present a global correlation chart for the marine Lopingian Series. Copyright © 2010 John Wiley & Sons, Ltd. [source] THE END-PERMIAN MASS EXTINCTION WAS SYNCHRONOUS COINCIDED WITH THE EVOLUTION OF TOXIC ALGAEJOURNAL OF PHYCOLOGY, Issue 2001Article first published online: 24 SEP 200 Lee, R. E.1 & Kugrens, P.2 1Department of Biomedical Sciences, College of Veterinary Medicine, Colorado State University, Fort Collins, CO 80523; 2Department of Biology, Colorado State University, Fort Collins, Co 80523 USA The cause of the end-Permian mass extinction, the greatest of all mass extinctions, is one of the most intriguing mysteries in the history of life. The end-Permian mass extinction was primarily a marine event, resulting principally in the elimination of sessile filter-feeding organisms. Based on two methods, molecular clocks and correlation with ancient atmospheric CO2, the algae derived from secondary endosymbioses are believed to have originated in the middle to late Permian. All of the toxic marine algae in today's oceans are derived from secondary endosymbioses. Therefore it appears likely that the end-Permian extinction was due to the evolution of toxic algae in the phytoplankton of late-Permian seas. Sieving of the toxic algae in the phytoplankton likely resulted in the decline and eventual elimination of a large portion of the Paleozoic fauna during the end-Permian mass extinction. [source] The two Early Toarcian (Early Jurassic) extinction events in ammonoidsLETHAIA, Issue 1 2004FABRIZIO CECCA The Early Toarcian (Early Jurassic) biological crisis was one of the ,minor' mass extinctions. It is linked with an oceanic anoxic event. Fossil data from sections located in northwestern European (epicontinental platforms and basins) and Tethyan (distal, epioceanic) areas indicate that Late Pliensbachian,Early Toarcian ammonoids experienced two extinction events during the Early Toarcian. The older one is linked with disruption of the Tethyan,Boreal provinciality, whereas the younger event correlates with the onset of anoxia and corresponds with the Early Toarcian mass-extinction event. These two extinctions cannot be interpreted as episodes of a single, stepwise, event. Values of the net diversification, more than the number of extinctions, allow the two extinction events to be clearly recognized and distinguished. Values of regional net diversification for northwestern European and Tethyan faunas point to greater evolutionary dynamics in the epioceanic areas. The inclusion of Mediterranean faunas in the database proves that the ammonite turnover at the Early Toarcian mass-extinction event was more important than previously thought. Progenitor (evolute Neolioceratoides), survivor (Dactylioceras, Polyplectus pluricostatus) and Lazarus (Procliviceras) taxa have been recognized. Different selectivity patterns are shown for the two events. The first one, linked to the disruption of the Tethyan,Boreal provinciality, has mainly affected ammonites adapted to epicontinental platforms. In the mass-extinction event, no selectivity is recognized, because also Phylloceratina and Lytoceratina were deeply affected at species level, although their wide biogeographical distribution at clade level was a significant buffer against extinction. In contrast to Palaeozoic mass extinctions, ammonoid survivors and Lazarus taxa are characterized by complex sutures: Phylloceratina (long-ranging ammonoids) and Polyplectus (relatively long-ranging compared to other Ammonitina). [source] Causes of mass extinctionsLETHAIA, Issue 3 2001GRZEGORZ RACKI No abstract is available for this article. [source] Catastrophic events and mass extinctions: Impacts and beyond Vienna, Austria 2000 July 9,12METEORITICS & PLANETARY SCIENCE, Issue 6 2000Graham Ryder [source] Phylogeography of lions (Panthera leo ssp.) reveals three distinct taxa and a late Pleistocene reduction in genetic diversityMOLECULAR ECOLOGY, Issue 8 2009ROSS BARNETT Abstract Lions were the most widespread carnivores in the late Pleistocene, ranging from southern Africa to the southern USA, but little is known about the evolutionary relationships among these Pleistocene populations or the dynamics that led to their extinction. Using ancient DNA techniques, we obtained mitochondrial sequences from 52 individuals sampled across the present and former range of lions. Phylogenetic analysis revealed three distinct clusters: (i) modern lions, Panthera leo; (ii) extinct Pleistocene cave lions, which formed a homogeneous population extending from Europe across Beringia (Siberia, Alaska and western Canada); and (iii) extinct American lions, which formed a separate population south of the Pleistocene ice sheets. The American lion appears to have become genetically isolated around 340 000 years ago, despite the apparent lack of significant barriers to gene flow with Beringian populations through much of the late Pleistocene. We found potential evidence of a severe population bottleneck in the cave lion during the previous interstadial, sometime after 48 000 years, adding to evidence from bison, mammoths, horses and brown bears that megafaunal populations underwent major genetic alterations throughout the last interstadial, potentially presaging the processes involved in the subsequent end-Pleistocene mass extinctions. [source] The Wildlife Picture Index: monitoring top trophic levelsANIMAL CONSERVATION, Issue 4 2010T. G. O'Brien Abstract Although recent biodiversity loss has been compared with cataclysmic mass extinctions, we still possess few indicators that can assess the extent or location of biodiversity loss on a global scale. The Convention on Biological Diversity (CBD) has mandated development of indicators that can meet the needs of monitoring biodiversity by 2010. To date, many indicators rely on unwarranted assumptions, secondary data, expert opinion and retrospective time series. We present a new biodiversity indicator, the Wildlife Picture Index (WPI) that targets medium and large-sized terrestrial birds and mammals in forested and savannah ecosystems that. The WPI is a composite indicator based on the geometric mean of relative occupancy estimates derived from camera trap sampling at a landscape scale. It has been designed to meet the needs of a CBD indicator while avoiding many of the pitfalls that characterize some CBD indicators. We present an example using 8 years of camera trap data from Bukit Barisan Selatan National Park, Indonesia to show that the WPI is capable of detecting changes in the rate of loss of biodiversity, a key requirement of a CBD indicator. We conclude that the WPI should be effective at monitoring top trophic levels in forest and savannah ecosystems using primary data and can fill the gap in knowledge about trends in tropical biodiversity. [source] Nearby stars of the Galactic disk and halo.ASTRONOMISCHE NACHRICHTEN, Issue 1 2004Abstract High-resolution spectroscopic observations of about 150 nearby stars or star systems are presented and discussed. The study of these and another 100 objects of the previous papers of this series implies that the Galaxy became reality 13 or 14 Gyr ago with the implementation of a massive, rotationally-supported population of thick-disk stars. The very high star formation rate in that phase gave rise to a rapid metal enrichment and an expulsion of gas in supernovae-driven Galactic winds, but was followed by a star formation gap for no less than three billion years at the Sun's galactocentric distance. In a second phase, then, the thin disk , our "familiar Milky Way" , came on stage. Nowadays it traces the bright side of the Galaxy, but it is also embedded in a huge coffin of dead thick-disk stars that account for a large amount of baryonic dark matter. As opposed to this, cold-dark-matter-dominated cosmologies that suggest a more gradual hierarchical buildup through mergers of minor structures, though popular, are a poor description for the Milky Way Galaxy , and by inference many other spirals as well , if, as the sample implies, the fossil records of its long-lived stars do not stick to this paradigm. Apart from this general picture that emerges with reference to the entire sample stars, a good deal of the present work is however also concerned with detailed discussions of many individual objects. Among the most interesting we mention the blue straggler or merger candidates HD 165401 and HD 137763/HD 137778, the likely accretion of a giant planet or brown dwarf on 59 Vir in its recent history, and HD 63433 that proves to be a young solar analog at , , 200 Myr. Likewise, the secondary to HR 4867, formerly suspected non-single from the Hipparcos astrometry, is directly detectable in the highresolution spectroscopic tracings, whereas the visual binary , Cet is instead at least triple, and presumably even quadruple. With respect to the nearby young stars a complete account of the UrsaMajor Association is presented, and we provide as well plain evidence for another, the "Hercules-Lyra Association", the likely existence of which was only realized in recent years. On account of its rotation, chemistry, and age we do confirm that the Sun is very typical among its G-type neighbors; as to its kinematics, it appears however not unlikely that the Sun's known low peculiar space velocity could indeed be the cause for the weak paleontological record of mass extinctions and major impact events on our parent planet during the most recent Galactic plane passage of the solar system. Although the significance of this correlation certainly remains a matter of debate for years to come, we point in this context to the principal importance of the thick disk for a complete census with respect to the local surface and volume densities. Other important effects that can be ascribed to this dark stellar population comprise (i) the observed plateau in the shape of the luminosity function of the local FGK stars, (ii) a small though systematic effect on the basic solar motion, (iii) a reassessment of the term "asymmetrical drift velocity" for the remainder (i.e. the thin disk) of the stellar objects, (iv) its ability to account for the bulk of the recently discovered high-velocity blue white dwarfs, (v) its major contribution to the Sun's ,220 km s,1 rotational velocity around the Galactic center, and (vi) the significant flattening that it imposes on the Milky Way's rotation curve. Finally we note a high multiplicity fraction in the small but volume-complete local sample of stars of this ancient population. This in turn is highly suggestive for a star formation scenario wherein the few existing single stellar objects might only arise from either late mergers or the dynamical ejection of former triple or higher level star systems. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||