Página 1 dos resultados de 306 itens digitais encontrados em 0.008 segundos

Cladistics and mass extinctions: the example of conulariids (Scyphozoa, Cnidaria) and the End Ordovician Extinction Event

Van Iten, Heyo; Burkey, Matthew; Basso, Juliana de Moraes Leme; Marques, Antonio Carlos
Fonte: Oxford Publicador: Oxford
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.41836%
The End Ordovician Extinction Event (EOEE) had little impact on supra-specific diversity and disparity within the order Conulariida (Scyphozoa, Cnidaria). With two possible exceptions (Exoconularia and Glyptoconularia), all eight genera currently known from strata of middle or late Katian age survived the crisis, and nearly all of the discontinuous gross morphological features present in Ordovician and older genera are present in at least one of the surviving genera.Acladistic parsimony analysis of 17 genera, 12 of which occur in Ordovician strata, produced 3 major subclades and 7 less inclusive subclades within Conulariida. With one possible exception, the clade Anaconularia þ Baccaconularia, all other monophyletic groups within Conulariida survived the EOEE. Moreover, additional, ghost lineages in the clade Climacoconus þ Holoconularia þ Notoconularia þ Paraconularia þ Reticulaconularia must have crossed the Ordovician–Silurian boundary. The minor impact of the EOEE on diversity and disparity within Conulariida probably reflects the eurytopic character and simple but efficient metabolism (possibly glycolysis-based) of this group.; Research Center of Marine Biodiversity of the University of São Paulo; CAPES; CNPq; FAPESP

Mass extinctions, galactic orbits in the solar neighborhood and the Sun: a connection?

Mello, G. F. Porto de; Dias, W. S.; Lepine, Jacques Raymond Daniel; Lorenzo-Oliveira, D.; Siqueira, R. K.
Fonte: International Astronomical Union; Florianópolis Publicador: International Astronomical Union; Florianópolis
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
47.97644%
The orbits of the stars in the disk of the Galaxy, and their passages through the Galactic spiral arms, are a rarely mentioned factor of biosphere stability which might be important for long-term planetary climate evolution, with a possible bearing on mass extinctions. The Sun lies very near the co-rotation radius, where stars revolve around the Galaxy in the same period as the density wave perturbations of the spiral arms. Conventional wisdom generally considers that this status makes for few passages through the spiral arms. Controversy still surrounds whether time spent inside or around spiral arms is dangerous to biospheres and conducive to mass extinctions. Possible threats include giant molecular clouds disturbing the Oort comet cloud and provoking heavy bombardment; a higher exposure to cosmic rays near star forming regions triggering increased cloudiness in Earth’s atmosphere and ice ages; and the destruction of Earth’s ozone layer posed by supernova explosions. We present detailed calculations of the history of spiral arm passages for all 212 solar-type stars nearer than 20 parsecs, including the total time spent inside the spiral arms in the last 500 Myr, when the spiral arm position can be traced with good accuracy. We found that there is a large diversity of stellar orbits in the solar neighborhood...

Lessons from the past: Evolutionary impacts of mass extinctions

Jablonski, David
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 08/05/2001 Português
Relevância na Pesquisa
48.079214%
Mass extinctions have played many evolutionary roles, involving differential survivorship or selectivity of taxa and traits, the disruption or preservation of evolutionary trends and ecosystem organization, and the promotion of taxonomic and morphological diversifications—often along unexpected trajectories—after the destruction or marginalization of once-dominant clades. The fossil record suggests that survivorship during mass extinctions is not strictly random, but it often fails to coincide with factors promoting survival during times of low extinction intensity. Although of very serious concern, present-day extinctions have not yet achieved the intensities seen in the Big Five mass extinctions of the geologic past, which each removed ≥50% of the subset of relatively abundant marine invertebrate genera. The best comparisons for predictive purposes therefore will involve factors such as differential extinction intensities among regions, clades, and functional groups, rules governing postextinction biotic interchanges and evolutionary dynamics, and analyses of the factors that cause taxa and evolutionary trends to continue unabated, to suffer setbacks but resume along the same trajectory, to survive only to fall into a marginal role or disappear (“dead clade walking”)...

Lessons from the past: Biotic recoveries from mass extinctions

Erwin, Douglas H.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 08/05/2001 Português
Relevância na Pesquisa
47.824727%
Although mass extinctions probably account for the disappearance of less than 5% of all extinct species, the evolutionary opportunities they have created have had a disproportionate effect on the history of life. Theoretical considerations and simulations have suggested that the empty niches created by a mass extinction should refill rapidly after extinction ameliorates. Under logistic models, this biotic rebound should be exponential, slowing as the environmental carrying capacity is approached. Empirical studies reveal a more complex dynamic, including positive feedback and an exponential growth phase during recoveries. Far from a model of refilling ecospace, mass extinctions appear to cause a collapse of ecospace, which must be rebuilt during recovery. Other generalities include the absence of a clear correlation between the magnitude of extinction and the pace of recovery or the resulting ecological and evolutionary disruption the presence of a survival interval, with few originations, immediately after an extinction and preceding the recovery phase, and the presence of many lineages that persist through an extinction event only to disappear during the subsequent recovery. Several recoveries include numerous missing lineages...

Survival without recovery after mass extinctions

Jablonski, David
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 11/06/2002 Português
Relevância na Pesquisa
48.224478%
Because many survivors of mass extinctions do not participate in postrecovery diversifications, and therefore fall into a pattern that can be termed “Dead Clade Walking” (DCW), the effects of mass extinctions extend beyond the losses observed during the event itself. Analyses at two taxonomic levels provide a first-order test of the prevalence of DCWs by using simple and very conservative operational criteria. For four of the Big Five mass extinctions of the Phanerozoic, the marine genera that survived the extinction suffered ≈10–20% attrition in the immediately following geologic stage that was significantly greater than the losses sustained in preextinction stages. The stages immediately following the three Paleozoic mass extinctions also account for 17% of all order-level losses in marine invertebrates over that interval, which is, again, significantly greater than that seen for the other stratigraphic stages (no orders are lost immediately after the end-Triassic or end-Cretaceous mass extinctions). DCWs are not evenly distributed among four regional molluscan time-series following the end-Cretaceous extinction, demonstrating the importance of spatial patterns in recovery dynamics. Although biotic interactions have been invoked to explain the differential postextinction success of clades...

A scale of greatness and causal classification of mass extinctions: Implications for mechanisms

Şengör, A. M. Celâl; Atayman, Saniye; Özeren, Sinan
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.816606%
A quantitative scale for measuring greatness, G, of mass extinctions is proposed on the basis of rate of biodiversity diminution expressed as the product of the loss of biodiversity, called magnitude (M), and the inverse of time in which that loss occurs, designated as intensity (I). On this scale, the catastrophic Cretaceous–Tertiary (K-T) extinction appears as the greatest since the Ordovician and the only one with a probable extraterrestrial cause. The end-Permian extinction was less great but with a large magnitude (M) and smaller intensity (I); only some of its individual episodes involved some semblance of catastrophe. Other extinctions during the Phanerozoic, with the possible exception of the end-Silurian diversity plunge, were parts of a forced oscillatory phenomenon and seem caused by marine- and land-habitat destruction during continental assemblies that led to elimination of shelves and (after the Devonian) rain forests and enlargement of deserts. Glaciations and orogenies that shortened and thickened the continental crust only exacerbated these effects. During the Mesozoic and Cainozoic, the evolution of life was linearly progressive, interrupted catastrophically only at the K-T boundary. The end-Triassic extinction was more like the Paleozoic extinctions in nature and probably also in its cause. By contrast...

Evidence from ammonoids and conodonts for multiple Early Triassic mass extinctions

Stanley, Steven M.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.97644%
Ammonoids and conodonts, being characterized by exceptionally high background rates of origination and extinction, were vulnerable to global environmental crises, which characteristically intensified background rates of extinction. Thus, it is not surprising that these taxa suffered conspicuous mass extinctions at the times of three negative Early Triassic global carbon isotopic excursions that resembled those associated with the two preceding Permian mass extinctions. In keeping with their high rates of origination, both the ammonoids and conodonts rediversified dramatically between the Early Triassic crises. Other marine taxa, characterized by much lower intrinsic rates of origination, were held at low levels of diversity by the Early Triassic crises; because global mass extinctions affect all marine life, these taxa must have experienced relatively modest expansions and contractions that have yet to be discovered, because they do not stand out in the fossil record and because the stratigraphic ranges of these taxa, being of little value for temporal correlation, have not been thoroughly studied.

A Comparison of the Effects of Random and Selective Mass Extinctions on Erosion of Evolutionary History in Communities of Digital Organisms

Yedid, Gabriel; Stredwick, Jason; Ofria, Charles A.; Agapow, Paul-Michael
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 31/05/2012 Português
Relevância na Pesquisa
47.816606%
The effect of mass extinctions on phylogenetic diversity and branching history of clades remains poorly understood in paleobiology. We examined the phylogenies of communities of digital organisms undergoing open-ended evolution as we subjected them to instantaneous “pulse” extinctions, choosing survivors at random, and to prolonged “press” extinctions involving a period of low resource availability. We measured age of the phylogenetic root and tree stemminess, and evaluated how branching history of the phylogenetic trees was affected by the extinction treatments. We found that strong random (pulse) and strong selective extinction (press) both left clear long-term signatures in root age distribution and tree stemminess, and eroded deep branching history to a greater degree than did weak extinction and control treatments. The widely-used Pybus-Harvey gamma statistic showed a clear short-term response to extinction and recovery, but differences between treatments diminished over time and did not show a long-term signature. The characteristics of post-extinction phylogenies were often affected as much by the recovery interval as by the extinction episode itself.

Evolutionary legacy response observed in algae and bryophytes following hydrogen sulfide administration

Gupta, E.; Dooley, F.D.; Ward, P.D.
Fonte: Taylor & Francis Publicador: Taylor & Francis
Tipo: Artigo de Revista Científica
Publicado em //2014 Português
Relevância na Pesquisa
47.824727%
The study presented here examined the effects of administering hydrogen sulfide(H2S) to several ancient extant plant species to determine the organisms’ response to stress. Even though sulfur is an essential macronutrient required for growth and productivity, there are toxic compounds of this element that exert detrimental effects and produce physiological stress. It is speculated that the accumulation of H2S,a lethal gas, may have been a major contributing factor in past mass extinction events, where the environment was fairly anoxic with fluctuating temperatures. The potential of this toxic compound to exist as an environmental stressor suggests that certain organisms may have adapted to survive these periods of mass extinctions. It is hypothesized that due to the abundant presence of H2S in the past, ancient land plants may have an adaptive advantage that allowed them to survive and thrive. In this study, species of bryophytes and algae were exposed to specific concentrations of aqueous H2S over a seven-day period and measured their photosynthetic capacity at timed intervals using a FluorCam. Studying the effects of this toxic gas on ancient plants is imperative to our understanding of sulfur’s varying biological roles, and provides insight on the evolutionary phenotypic variations amongst plants and stress responses in order to survive mass extinctions. Results indicate that Hypnum...

Mass extinctions, galactic orbits in the solar neighborhood and the Sun: a connection?

Mello, Gustavo F. Porto de; Dias, Wilson S.; Lepine, Jacques Raymond Daniel
Fonte: Guarujá Publicador: Guarujá
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
47.97644%
The orbits of the stars in the disk of the Galaxy, and their passages through the Galactic spiral arms, are a rarely mentioned factor of biosphere stability which might be important for long-term planetary climate evolution, with a possible bearing on mass extinctions. The Sun lies very near the co-rotation radius, where stars revolve around the Galaxy in the same period as the density wave perturbations of the spiral arms. conventional wisdom generally considers that this status makes for few passages through the spiral arms. Controversy still surrounds whether time spent inside or around spiral arms is dangerous to biospheres and conductive to mass extinctions. Possible threats include giant molecular clouds disturbing the Oort comet cloud and provoking heavy bombardment: a higher exposure to cosmic rays near star forming regions triggering increased cloudiness in Earth atmosphere and ice ages; and the desctruction of Earth's ozone layer posed by supernova explosiosn. We present detailed calculations of the history of spiral arm passages for all 212 solar-type stars nearer than 20 parsecs, including the total time spent inside armsin the last 500 Myr, when the spiral arm position can be traced with good accuracy. We found that there is a large diversity of stellar orbits in the solar neighborhood...

Mass extinctions: an alternative to the Allee effect

Schinazi, Rinaldo B.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/03/2005 Português
Relevância na Pesquisa
47.41836%
We introduce a spatial stochastic process on the lattice Z^d to model mass extinctions. Each site of the lattice may host a flock of up to N individuals. Each individual may give birth to a new individual at the same site at rate \phi until the maximum of N individuals has been reached at the site. Once the flock reaches N individuals, then, and only then, it starts giving birth on each of the 2d neighboring sites at rate \lambda(N). Finally, disaster strikes at rate 1, that is, the whole flock disappears. Our model shows that, at least in theory, there is a critical maximum flock size above which a species is certain to disappear and below which it may survive.; Comment: Published at http://dx.doi.org/10.1214/105051604000000819 in the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org)

The tectonic cause of mass extinctions and the genomic contribution to biodiversification

Li, Dirson Jian
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/12/2012 Português
Relevância na Pesquisa
48.017686%
Despite numerous mass extinctions in the Phanerozoic eon, the overall trend in biodiversity evolution was not blocked and the life has never been wiped out. Almost all possible catastrophic events (large igneous province, asteroid impact, climate change, regression and transgression, anoxia, acidification, sudden release of methane clathrate, multi-cause etc.) have been proposed to explain the mass extinctions. However, we should, above all, clarify at what timescale and at what possible levels should we explain the mass extinction? Even though the mass extinctions occurred at short-timescale and at the species level, we reveal that their cause should be explained in a broader context at tectonic timescale and at both the molecular level and the species level. The main result in this paper is that the Phanerozoic biodiversity evolution has been explained by reconstructing the Sepkoski curve based on climatic, eustatic and genomic data. Consequently, we point out that the P-Tr extinction was caused by the tectonically originated climate instability. We also clarify that the overall trend of biodiversification originated from the underlying genome size evolution, and that the fluctuation of biodiversity originated from the interactions among the earth's spheres. The evolution at molecular level had played a significant role for the survival of life from environmental disasters.; Comment: 64 pages...

Mass Extinctions vs. Uniformitarianism in Biological Evolution

Bak, Per; Paczuski, Maya
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/02/1996 Português
Relevância na Pesquisa
47.76384%
It is usually believed that Darwin's theory leads to a smooth gradual evolution, so that mass extinctions must be caused by external shocks. However, it has recently been argued that mass extinctions arise from the intrinsic dynamics of Darwinian evolution. Species become extinct when swept by intermittent avalanches propagating through the global ecology. These ideas are made concrete through studies of simple mathematical models of coevolving species. The models exhibit self-organized criticality and describe some general features of the extinction pattern in the fossil record.; Comment: 17 pages uuencoded with style file lamuphys.sty. 9 figures not included but can be obtained via bak@cmth.phy.bnl.gov. to appear in ``Physics of Biological Systems'' Lecture Notes in Physics (Springer-Verlag, Heidelberg , 1996)

Detecting patterns of species diversification in the presence of both rate shifts and mass extinctions

Laurent, Sacha; Robinson-Rechavi, Marc; Salamin, Nicolas
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.97644%
Recent methodological advances are enabling better examination of speciation and extinction processes and patterns. A major open question is the origin of large discrepancies in species number between groups of the same age. Existing frameworks to model this diversity either focus on changes between lineages, neglecting global effects such as mass extinctions, or focus on changes over time which would affect all lineages. Yet it seems probable that both lineages differences and mass extinctions affect the same groups. Here we used simulations to test the performance of two widely used methods, under complex scenarios. We report good performances, although with a tendency to over-predict events when increasing the complexity of the scenario. Overall, we find that lineage shifts are better detected than mass extinctions. This work has significance for assessing the methods currently used for estimating changes in diversification using phylogenies and developing new tests.; Comment: 34 pages, 11 figures

Long-term evolution of an ecosystem with spontaneous periodicity of mass extinctions

Lipowski, Adam; Lipowska, Dorota
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
47.76384%
Twenty years ago, after analysing palaeontological data, Raup and Sepkoski suggested that mass extinctions on Earth appear cyclically in time with a period of approximately 26 million years (My). To explain the 26My period, a number of proposals were made involving, e.g., astronomical effects, increased volcanic activity, or the Earth's magnetic field reversal, none of which, however, has been confirmed. Here we study a spatially extended discrete model of an ecosystem and show that the periodicity of mass extinctions might be a natural feature of the ecosystem's dynamics and not the result of a periodic external perturbation. In our model, periodic changes of the diversity of an ecosystem and some of its other characteristics are induced by the coevolution of species. In agreement with some palaeontological data, our results show that the longevity of a species depends on the evolutionary stage at which the species is created. Possible further tests of our model are also discussed.; Comment: 10 pages, Theory in Biosciences (in press). For associated Java applet see http://spin.amu.edu.pl/~lipowski/prey_pred.html

Volcanogenic Dark Matter and Mass Extinctions

Abbas, Samar; Abbas, Afsar
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/12/1996 Português
Relevância na Pesquisa
47.76384%
The passage of the Earth through dense clumps of dark matter, the presence of which are predicted by certain cosmologies, would produce large quantities of heat in the interior of this planet through the capture and subsequent annihilation of dark matter particles. This heat can cause large-scale volcanism which could in turn have caused the extinction of the dinosaurs and other mass extinctions. The periodicity of such volcanic outbursts agrees with the frequency of palaeontological mass extinctions as well as the observed periodicity in the occurrence of the largest flood basalt provinces on the globe.; Comment: 6 pages in Latex file

Mass Extinctions and The Sun's Encounters with Spiral Arms

Leitch, Erik M.; Vasisht, Gautam
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/02/1998 Português
Relevância na Pesquisa
47.816606%
The terrestrial fossil record shows that the exponential rise in biodiversity since the Precambrian period has been punctuated by large extinctions, at intervals of 40 to 140 Myr. These mass extinctions represent extremes over a background of smaller events and the natural process of species extinction. We point out that the non-terrestrial phenomena proposed to explain these events, such as boloidal impacts (a candidate for the end-Cretaceous extinction), and nearby supernovae, are collectively far more effective during the solar system's traversal of spiral arms. Using the best available data on the location and kinematics of the Galactic spiral structure (including distance scale and kinematic uncertainties), we present evidence that arm crossings provide a viable explanation for the timing of the large extinctions.; Comment: Latex, aaspp4.sty, 8 pages, 2 Postscript figures, to appear in New Astronomy 3 (1998) 51-56

Tidal Effects of Passing Planets and Mass Extinctions

Fargion, Daniele; Dar, Arnon
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/02/1998 Português
Relevância na Pesquisa
47.517305%
Recent observations suggest that many planetary-mass objects may be present in the outer solar system between the Kuiper belt and the Oort cloud. Gravitational perturbations may occasionally bring them into the inner solar system. Their passage near Earth could have generated gigantic tidal waves, large volcanic eruptions, sea regressions, large meteoritic impacts and drastic changes in global climate. They could have caused the major biological mass extinctions in the past 600 My as documented in the geological records.

Double Mass Extinctions and the Volcanogenic Dark Matter Scenario

Abbas, Samar; Abbas, Afsar; Mohanty, Shukadev
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/05/1998 Português
Relevância na Pesquisa
47.91555%
A few of the major mass extinctions of paleontology have recently been found to consist of two distinct extinction peaks at higher resolution. A viable explanation for this remains elusive. In this paper it is shown that the recently proposed volcanogenic dark matter model can explain this puzzling characteristic of these extinctions. The accumulation and annihilation of dark matter in the center of the Earth due to the passage of a clump leads to excess heat generation with the consequent ejection of superplumes, followed by massive volcanism and attendant mass extinctions. This is preceded by an extinction pulse due to carcinogenesis arising from the direct interaction of the clumped dark matter with living organisms.; Comment: 11 pages, RevTeX, no figures

Asteroid/comet impact clusters, flood basalts and mass extinctions: Significance of isotopic age overlaps

Glikson, Andrew
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
57.89576%
Morgan et al. [J. Phipps Morgan, T.J. Reston, C.R. Ranero. Earth Planet. Sci. Lett. 217 (2004) 263-284.], referring to an overlap between the isotopic ages of volcanic events and four epoch/stage extinction boundaries, suggest a dominant role of Continental Flood Basalts (CFB) and of explosive CO2-rich volcanic pipes ("Verneshots") as mass extinction triggers. Here I point out that Morgan et al. overlook 3 overlaps between the ages of extraterrestrial impacts, volcanic and mass extinction events, and 3 overlaps between the ages of extraterrestrial impact and volcanic events. These overlaps suggest that both extraterrestrial impacts and volcanism served as extinction triggers separately or in combination. A protracted impact cluster overlaps extinctions at the end-Devonian (∼374-359 Ma) and impact-extinction age overlaps occur in the end-Jurassic (∼145-142 Ma), Aptian (∼125-112 Ma); Cenomanian-Turonian (∼95-94 Ma); K-T boundary (∼65.5 Ma) and mid-Miocene (∼16 Ma) (Table 1). Morgan et al. appear to question the uniqueness of shock metamorphic and geochemical criteria used to identify asteroid/comet impacts. However, shock pressures at 8-35 GPa, indicated by intra-crystalline planar deformation features (PDF), exceed lithospheric and volcanic explosion pressures by an order of magnitude and are not known to be associated with explosive volcanic diatremes...