نتایج جستجو برای: permian
تعداد نتایج: 3143 فیلتر نتایج به سال:
The Bedout High, located on the northwestern continental margin of Australia, has emerged as a prime candidate for an end-Permian impact structure. Seismic imaging, gravity data, and the identification of melt rocks and impact breccias from drill cores located on top of Bedout are consistent with the presence of a buried impact crater. The impact breccias contain nearly pure silica glass (SiO2)...
Global fossil data show that profound biodiversity loss preceded the final catastrophe that killed nearly 90% marine species on a global scale at the end of the Permian. Many hypotheses have been proposed to explain this extinction and yet still remain greatly debated. Here, we report analyses of all four sulphur isotopes ((32)S, (33)S, (34)S and (36)S) for pyrites in sedimentary rocks from the...
M. J. S. Rudwick and others postulate ‘rhythmic-flow’ feeding for the Permian richthofeniacean bi-achiopods, whereas R. E. Grant claims that they fed by normal ciliary action. Suspension-feeding has two components, current generation and food capture; normal brachiopod lophophores d o both, but this is neither universal nor compulsory among animals. Opening and closing the richthofeniid shell g...
The Karoo Basin has long been considered to contain the type stratigraphic succession for the terrestrial expression of the end-Permian mass extinction. A detailed extinction model, based on biostratigraphic and geologic data, has proposed rapid environmental change that coincides with a vertebrate biozone boundary, which was postulated to have been caused by increased aridity. Our sedimentolog...
In response to predation pressure, some insects have developed spectacular plant mimicry strategies (homomorphy), involving important changes in their morphology. The fossil record of plant mimicry provides clues to the importance of predation pressure in the deep past. Surprisingly, to date, the oldest confirmed records of insect leaf mimicry are Mesozoic. Here we document a crucial step in th...
Burial and exhumation historyof Pennsylvanian strata, central Appalachian basin: an integrated study
An inferred burial and exhumation history of Pennsylvanian strata in the central Appalachian foreland basin is constrained by integrating palaeothermometers, geochronometers and estimated palaeogeothermal gradients.Vitrinite re£ectance data and £uid inclusion homogenization temperatures indicate that burial ofLower andUpperPennsylvanian strata of theAppalachianPlateau inWest Virginia exceeded 4...
It has been argued that increases in predation over geological time should result in increases in defensive adaptations in prey taxa. Recent in situ and laboratory observations indicate that cidaroid sea urchins feed on live stalked crinoids, leaving distinct bite marks on their skeletal elements. Similar bite marks on fossil crinoids from Poland strongly suggest that these animals have been su...
The terminal Paleozoic fungal event: evidence of terrestrial ecosystem destabilization and collapse.
Because of its prominent role in global biomass storage, land vegetation is the most obvious biota to be investigated for records of dramatic ecologic crisis in Earth history. There is accumulating evidence that, throughout the world, sedimentary organic matter preserved in latest Permian deposits is characterized by unparalleled abundances of fungal remains, irrespective of depositional enviro...
Fungi today occur on virtually every plant part, living and dead, and represent a significant proportion of fungal diversity. Arborescent seed ferns characterized by large, tongue-shaped leaves with reticulate venation (Glossopteris) represent the dominant floral element in the Permian of Gondwana. However, documented evidence of fungi associated with the leaves of these plants is exceedingly r...
Today, cycads are a small group of gymnospermous plants with a limited distribution in the (sub)tropics, but they were major constituents of Mesozoic floras. Fossil leaves sporadically found in latest Carboniferous and Permian floras have putatively been ascribed to cycads. However, their true affinity remains unclear due to the lack of anatomical evidence. Virtually all modern cycads have pinn...
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