Linking carbon cycle perturbations to the Late Ordovician glaciation and mass extinction: A modeling approach
Junpeng ZhangChao LiYangyang ZhongXuejin WuXiang FangMu LiuDaizhao ChenBenjamin C. GillThomas J. AlgeoTimothy W. LyonsYuandong ZhangHui Tian
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Extinction (optical mineralogy)
At the end of the Ordovician many marine benthonic and planktonic faunas underwent a global extinction that has been attributed to climatic changes and glacio-eustatic fluctuations in sea-level (Berry and Boucot, 1973; Sheehan, 1973, 1975; Brenchley, 1984). Raup and Sepkoski (1982) found that the Late Ordovician-Early Silurian extinction event was one of the five major Phanerozoic mass extinctions.
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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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Abstract The second largest Phanerozoic mass extinction occurred at the Ordovician-Silurian (O-S) boundary. However, unlike the other major mass extinction events, the driver for the O-S extinction remains uncertain. The abundance of mercury (Hg) and total organic carbon (TOC) of Ordovician and early Silurian marine sediments were analyzed from four sections (Huanghuachang, Chenjiahe, Wangjiawan and Dingjiapo) in the Yichang area, South China, as a test for evidence of massive volcanism associated with the O-S event. Our results indicate the Hg concentrations generally vary in parallel with TOC, and that the Hg/TOC ratios remain low and steady state through the Early and Middle Ordovician. However, Hg concentrations and the Hg/TOC ratio increased rapidly in the Late Katian, and have a second peak during the Late Hirnantian (Late Ordovician) that was temporally coincident with two main pulses of mass extinction. Hg isotope data display little to no variation associated with the Hg spikes during the extinction intervals, indicating that the observed Hg spikes are from a volcanic source. These results suggest intense volcanism occurred during the Late Ordovician, and as in other Phanerozoic extinctions, likely played an important role in the O-S event.
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It has long been appreciated that the rates of extinction recorded in the fossil record have not remained constant through time, but only during the last few decades has this variation been more clearly quantified. Much of this has been due to the single-handed efforts of the late Jack Sepkoski of the University of Chicago. Sepkoski spent 'ten years in the library' sifting through palaeontological publications and amassing a vast database on the first and last appearances of fossil groups (Sepkoski, 1994). Initially this work concentrated on families of organisms, but it was subsequently up-dated to include the first and last appearances of genera. Plotting last appearances (extinctions) against time revealed several distinctive features (Figure 5.1). Firstly extinction rates appear to have been considerably higher in the earlier part of the fossil record, particularly in the Cambrian Period. This is, at least partly, an artefact of the way extinction rates are measured. Diversity in the Cambrian was relatively low, particularly compared with the levels achieved in the Mesozoic and Cenozoic, with the result that relatively few organisms needed to go extinct to achieve a relatively high extinction percentage (see also Chapter 1).
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Abstract Strata of the Solvik Formation in the central Oslo Region (upper Hirnantian through most of Aeronian) are very fossiliferous and provide a good record relating to the survival and recovery faunas after the end-Ordovician mass extinctions. The ribbed atrypide fauna is especially rich with 21 species present. Samples from most of these taxa have been sectioned to reveal internal structures for taxonomic study. Of these, 13 species belong to the family Atrypidae, three of which are described in the present paper; Dihelictera engerensis n. sp., Gotatrypa vettrensis n. sp., and Rhinatrypa henningsmoeni n. gen. The family Atrypidae follows a global pattern of recovery with an increase in diversity registered in upper Rhuddanian and further diversification in Aeronian strata. The focus of this paper is the family Atrypinidae, which shows a different pattern. They are common and fairly diverse near the base of the Rhuddanian in deeper waters and rare further up, especially in the Aeronian. One new genus, Bockeliena , and two new species, Plectatrypa rindi and Euroatrypa ? sigridi are defined. The relationship between the subfamilies Spirigerininae and Plectatrypinae is clarified through thin sections of material from the Ordovician/Silurian boundary layers. The plectatrypids originated in Baltica through transitional species found in upper Katian to Hirnantian strata leading from the cosmopolitan Eospirigerina to the Plectatrypa lineage with imbricate ribbing and, separately, to Bockeliena and others with lamellose, widely spaced ornamentation. The Oslo Region probably acted as a nexus for survival and spread of brachiopods after the end-Ordovician mass extinction. UUID: http://zoobank.org/95340b41-5537-4192-9338-211a2940bea8 .
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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.
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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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The oft-repeated claim that Earth's biota is entering a sixth "mass extinction" depends on clearly demonstrating that current extinction rates are far above the "background" rates prevailing between the five previous mass extinctions. Earlier estimates of extinction rates have been criticized for using assumptions that might overestimate the severity of the extinction crisis. We assess, using extremely conservative assumptions, whether human activities are causing a mass extinction. First, we use a recent estimate of a background rate of 2 mammal extinctions per 10,000 species per 100 years (that is, 2 E/MSY), which is twice as high as widely used previous estimates. We then compare this rate with the current rate of mammal and vertebrate extinctions. The latter is conservatively low because listing a species as extinct requires meeting stringent criteria. Even under our assumptions, which would tend to minimize evidence of an incipient mass extinction, the average rate of vertebrate species loss over the last century is up to 100 times higher than the background rate. Under the 2 E/MSY background rate, the number of species that have gone extinct in the last century would have taken, depending on the vertebrate taxon, between 800 and 10,000 years to disappear. These estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way. Averting a dramatic decay of biodiversity and the subsequent loss of ecosystem services is still possible through intensified conservation efforts, but that window of opportunity is rapidly closing.
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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.
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