Mass extinction: evolution and the effects of external influences on unfit species
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We present a new model for extinction in which species evolve in bursts or ‘avalanches’, during which they become on average more susceptible to environmental stresses such as harsh climates and so are more easily rendered extinct. Results of simulations and analytic calculations using our model show a powerlaw distribution of extinction sizes which is in reasonable agreement with fossil data. We also see several features qualitatively similar to those seen in the fossil record. For example, we see frequent smaller extinctions in the wake of a large mass extinction which arise because there is reduced competition for resources in the aftermath of a large extinction event, so species which would not normally be able to compete can get a foothold, but only until the next cold winter or bad attack of influenza comes along to wipe them out.Keywords:
Extinction (optical mineralogy)
Fossil Record
Abstract The Capitanian (Middle Permian) mass extinction event, prior to and separate from the end-Permian mass extinction, has been suggested as a severe biotic crisis comparable to the big five mass extinctions of the Phanerozoic. However, there is still controversy about its global significance. In particular, this purportedly disastrous event in the Capitanian was mostly documented in the eastern Tethys, especially South China and Japan, whereas its extent in higher latitudinal regions remains unclear. A few recent studies have reported biostratigraphic and chemostratigraphic evidence for the Capitanian extinction at the northwestern marginal shelf of Pangea, including in the Kapp Starostin Formation in Spitsbergen. However, we here report a different result from these previous studies based on a study of abundant brachiopod fossils collected from eight geological sections that represent the same formation in western and central Spitsbergen, Arctic Norway. Our biostratigraphic investigation recognizes a total of five brachiopod assemblages from the type section of the Kapp Starostin Formation at Festningen in Spitsbergen. The most striking biotic change in species composition is observed at the interval between the lowermost Vøringen Member (late Artinskian) and its overlying member (Kungurian) of the Kapp Starostin Formation in Spitsbergen, which makes it much earlier than the Capitanian. A similar faunal shift at the same stratigraphic interval is also observed from bryozoan-based biostratigraphic data. This faunal turnover could be linked to a significant climatic shift (cooling) along the northwestern margin of Pangea during the Artinskian−Kungurian. Specifically, it is inferred that a climatic perturbation (cooling) likely drove the extirpation (emigration) of marine faunas out of Spitsbergen and dispersal eastward into some lower latitudinal and climatically more habitable areas. Our result indicates that the Capitanian interval in Spitsbergen does not record a catastrophic event that corresponds to the Capitanian mass extinction in Tethyan regions but rather marks gradual faunal transitions throughout the Middle to Late Permian. This faunal transition, driven by continuous cooling, was accompanied by major changes in regional lithology, which suggest a degree of local environmental control, especially in the changes of substrate and water depth, on the composition of the benthic faunas. The Wegener Halvø and Schuchert Dal Formations (Lopingian) in central East Greenland contain a diverse brachiopod fauna that is comparable to that of the post-Vøringen Member in Spitsbergen. This implies that the brachiopods in the northwestern marginal shelf of Pangea did not suffer a severe mass extinction in the Capitanian; instead, many of them migrated southward with the development of the Zechstein seaway.
Extinction (optical mineralogy)
Permian–Triassic extinction event
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Abstract Based on fossil mammals from North America, extinction rates since the last mass extinction, but before human influences, are estimated at 0.4 species/species/million years, which implies a species typically persisted for about 2.5 million years. The background extinction rate has been punctuated by mass extinctions, which are defined as more than 75% of species in the fossil record going extinct over a relatively short period of time, the last of which was 66 million years ago. Over the past 50,000 years humans have caused extinctions of at least 30% of large mammals, and at least 30% of Pacific island bird species. Over the past 500 years, between 1% and 5% of all remaining vertebrates on continents have been lost, which is 50 to 250 times faster than the estimated background rate of fossil mammals and implies that we will reach mass extinction levels within a few thousand years. This time will be shorter if current extinction rates are underestimated, or rates increase in the future.
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Fossil Record
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The Late Devonian envelops one of Earth’s big five mass extinction events at the Frasnian–Famennian boundary (374 Ma). Environmental change across the extinction severely affected Devonian reef-builders, besides many other forms of marine life. Yet, cause-and-effect chains leading to the extinction remain poorly constrained as Late Devonian stratigraphy is poorly resolved, compared to younger cataclysmic intervals. In this study we present a global orbitally calibrated chronology across this momentous interval, applying cyclostratigraphic techniques. Our timescale stipulates that 600 kyr separate the lower and upper Kellwasser positive δ13C excursions. The latter excursion is paced by obliquity and is therein similar to Mesozoic intervals of environmental upheaval, like the Cretaceous Ocean-Anoxic-Event-2 (OAE-2). This obliquity signature implies coincidence with a minimum of the 2.4 Myr eccentricity cycle, during which obliquity prevails over precession, and highlights the decisive role of astronomically forced “Milankovitch” climate change in timing and pacing the Late Devonian mass extinction.
Milankovitch cycles
Late Devonian extinction
Devonian
Cyclostratigraphy
Extinction (optical mineralogy)
Precession
Eccentricity (behavior)
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Extinction (optical mineralogy)
Extinction debt
Fossil Record
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The diversity of the brachiopods in the Northern Caucasus significantly fluctuated throughout the Paleozoic-Mesozoic. Weak diversifications occurred in the Middle Cambrian, Late Silurian - Early Devonian, and Late Devonian - Early Carboniferous. Since the Late Permian brachiopod assemblages became quite diverse. The maximum number of species was reached in the Rhaetian. The Permian/ Triassic mass extinction and enigmatic Ladinian crisis, on the other hand, led to regional brachiopod demises. In the Jurassic - Early Cretaceous interval the diversity of brachiopods generally decreased. The strongest drops of species numbers occurred in the Toarcian and Berriasian following the Pliensbachian-Toarcian and end-Jurassic global mass extinctions, and in the Kimmeridgian due to the regional salinity crisis. It is evident that some of the regional brachiopod diversifications coincided with the development of rimmed shelves.
Devonian
Ladinian
Late Devonian extinction
Permian–Triassic extinction event
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We present a new model for extinction in which species evolve in bursts or `avalanches', during which they become on average more susceptible to environmental stresses such as harsh climates and so are more easily rendered extinct. Results of simulations and analytic calculations using our model show a power-law distribution of extinction sizes which is in reasonable agreement with fossil data. e also see a number of features qualitatively similar to those seen in the fossil record. For example, we see frequent smaller extinctions in the wake of a large mass extinction, which arise because there is reduced competition for resources in the aftermath of a large extinction event, so that species which would not normally be able to compete can get a foothold, but only until the next cold winter or bad attack of the flu comes along to wipe them out.
Extinction (optical mineralogy)
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A new genus, Meishanorhynchia , is proposed based on new material from the Lower Triassic of the Meishan section, South China. It is of a late Griesbachian age based on both associated biozones (ammonoids and bivalves) and radiometric dates of the intercalated volcanic ash beds. Comparison with both Palaeozoic and Mesozoic–Cenozoic‐related genera suggests that it may represent the first radiation of progenitor brachiopods in the aftermath of the end‐Permian extinction. The lowest brachiopod horizon that contains the genus is estimated to be about 250.1 ± 0.3 Ma. This implies that the initial stage of recovery of Brachiopoda in the Early Triassic was probably about 1.3 ± 0.3 myr after the major pulse of the end‐Permian mass extinction (dated as 251.4 ± 0.3 Ma). This is in agreement with Hallam’s expectancy that biotic recovery typically begins within one million years or so of major mass extinctions, in contrast to current views on the end‐Permian extinction event which propose that the recovery of most if not all biotic groups in the Early Triassic was severely delayed and only began about five million years after the end‐Permian extinction.
Permian–Triassic extinction event
Early Triassic
Extinction (optical mineralogy)
Biozone
Conodont
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Several abrupt changes in conodont biofacies are documented to occur synchronously at six primary control sections across the Frasnian-Famennian boundary in Euramerica. These changes occurred within a time-span of only about 100,000 years near the end of the latest Frasnian linguiformis Zone, which is formally named to replace the Uppermost gigas Zone. The conodont-biofacies changes are interpreted to reflect a eustatic rise followed by an abrupt eustatic fall immediately preceding the late Frasnian mass extinction. Two new conodont species are named and described. Ancyrognathus ubiquitus n.sp. is recorded only just below and above the level of late Frasnian extinction and hence is a global marker for that event. Palmatolepispraetriangularis n.sp. is the long-sought Frasnian ancestor of the formerly cryptogenic species, Pa. triangularis, indicator of the earliest Famennian Lower triangularis Zone. The actual extinction event occurred entirely within the Frasnian and is interpreted to have been of brief duration-from as long as 20,000 years to as short as several days. The eustatic rise-and-fall couplet associated with the late Frasnian mass extinction is similar to eustatic couplets associated with the demise of most Frasnian (F2h) reefs worldwide about 1 m.y. earlier and with a latest Famennian mass extinction about 9.5 m.y. later. All these events may be directly or indirectly attributable to extraterrestrial triggering mechanisms. An impact of a small bolide or a near miss of a larger bolide may have caused the earlier demise of Frasnian reefs. An impact of possibly the same larger bolide in the Southern Hemisphere would explain the late Frasnian mass extinction. Global regression during the Famennian probably resulted from Southern-Hemisphere glaciation triggered by the latest Frasnian impact. Glaciation probably was the indirect cause of the latest Famennian mass extinction.
Conodont
Late Devonian extinction
Extinction (optical mineralogy)
Demise
Subaerial
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Mass extinction events are recognized by increases in extinction rate and magnitude and, often, by changes in the selectivity of extinction. When considering the selective fingerprint of a particular event, not all taxon extinctions are equally informative: some would be expected even under a ‘background’ selectivity regime, whereas others would not and thus require special explanation. When evaluating possible drivers for the extinction event, the latter group is of particular interest. Here, we introduce a simple method for identifying these most surprising victims of extinction events by training models on background extinction intervals and using these models to make per-taxon assessments of ‘expected’ risk during the extinction interval. As an example, we examine brachiopod genus extinctions during the Late Ordovician Mass Extinction and show that extinction of genera in the deep-water ‘ Foliomena fauna’ was particularly unexpected given preceding Late Ordovician extinction patterns.
Extinction (optical mineralogy)
Origination
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Abstract The Late Ordovician mass extinction was one of the five outstanding mass extinctions in Earth history. It was caused by environmental changes linked to exceptionally large climatic shifts and resulted in a massive elimination of species, but no major lasting changes in ecological structure or evolutionary direction.
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