Capitanian mass extinction event

In the aftermath of Olson's Extinction, global diversity rose during the Capitanian. This was probably the result of disaster taxa replacing extinct guilds. The Capitanian mass extinction greatly reduced disparity (the range of different guilds); eight guilds were lost. It impacted the diversity within individual communities more severely than the Permian–Triassic extinction event. rebuilding complex trophic structures and refilling guilds, Marine ecosystems The impact of the Capitanian extinction event on marine ecosystems is still heavily debated by palaeontologists. Early estimates indicated a loss of marine invertebrate genera between 35 and 47%, while an estimate published in 2016 suggested a loss of 33–35% of marine genera when corrected for background extinction, the Signor–Lipps effect and clustering of extinctions in certain taxa. The loss of marine invertebrates during the Capitanian mass extinction was comparable in magnitude to the Cretaceous–Paleogene extinction event. Terrestrial ecosystems Few published estimates for the impact on terrestrial ecosystems exist for the Capitanian mass extinction. Among vertebrates, Day and colleagues suggested a 74–80% loss of generic richness in tetrapods of the Karoo Basin in South Africa, including the extinction of the dinocephalians. In land plants, Stevens and colleagues found an extinction of 56% of plant species recorded in the mid-Upper Shihhotse Formation in North China, which was approximately mid-Capitanian in age. 24% of plant species in South China went extinct. == Timing ==

Although it is known that the Capitanian mass extinction occurred after Olson's Extinction and before the Permian–Triassic extinction event, the exact age of the Capitanian mass extinction remains controversial. Part of the reason for this is the poorly resolved biostratigraphy of the Guadalupian-Lopingian boundary interval. It is also partly due to the somewhat circumstantial age of the Capitanian–Wuchiapingian boundary itself, which is currently estimated to be approximately 259.1 million years old, but is subject to change by the Subcommission on Permian Stratigraphy of the International Commission on Stratigraphy. Additionally, there is a dispute regarding the severity of the extinction and whether the extinction in China happened at the same time as the extinction in Spitsbergen. Another study examining fossiliferous facies in Svalbard found no evidence for a sudden mass extinction, instead attributing local biotic changes during the Capitanian to the southward migration of many taxa through the Zechstein Sea. Carbonate platform deposits in Hungary and Hydra show no sign of an extinction event at the end of the Capitanian; the extinction event there is recorded in the middle Capitanian. The volcanics of the Emeishan Traps, which are interbedded with tropical carbonate platforms of the Maokou Formation, are unique for preserving a mass extinction and the cause of that mass extinction. this fits broadly with radiometric ages from the terrestrial realm, assuming the two events are contemporaneous. Plant losses occurred either at the same time as the marine extinction or after it. Marine realm The extinction of fusulinacean foraminifera in Southwest China was originally dated to the end of the Guadalupian, but studies published in 2009 and 2010 dated the extinction of these fusulinaceans to the mid-Capitanian. Brachiopod and coral losses occurred in the middle of the Capitanian stage. The extinction suffered by the ammonoids may have occurred in the early Wuchiapingian. and later the Dinocephalian Superassemblage and the Theriodontian Superassemblage, respectively. In South Africa, this corresponded to the boundary between the variously named Pareiasaurus, Dinocephalian or Tapinocephalus Assemblage Zone and the overlying assemblages. In both Russia and South Africa, this transition was associated with the extinction of the previously dominant group of therapsid amniotes, the dinocephalians, which led to its later designation as the dinocephalian extinction. Post-extinction origination rates remained low through the Pristerognathus Assemblage Zone for at least 1 million years, which suggests that there was a delayed recovery of Karoo Basin ecosystems. After the recognition of a separate marine mass extinction at the end of the Guadalupian, the dinocephalian extinction was seen to represent its terrestrial correlate. Though it was subsequently suggested that because the Russian Ischeevo fauna, which was considered the youngest dinocephalian fauna in that region, was constrained to below the Illawarra magnetic reversal and therefore had to have occurred in the Wordian stage, well before the end of the Guadalupian, and the retrieval of biostratigraphically radiometric ages via uranium–lead dating of a tuff from the Tapinocephalus Assemblage Zone of the Karoo Basin demonstrated that the dinocephalian extinction did occur in the late Capitanian, around 260 million years ago. == Effects on life ==

Marine life In the oceans, the Capitanian extinction event led to high extinction rates among ammonoids, corals and calcareous algal reef-building organisms, foraminifera, bryozoans, and brachiopods. It was more severe in restricted marine basins than in the open oceans. It appears to have been particularly selective against shallow-water taxa that relied on photosynthesis or a photosymbiotic relationship; many species with poorly buffered respiratory physiologies also became extinct. The extinction event led to a collapse of the reef carbonate factory in the shallow seas surrounding South China. The ammonoids, which had been in a long-term decline for a 30 million year period since the Roadian, suffered a selective extinction pulse at the end of the Capitanian. Among bivalve losses, perhaps most prominent were the giant alatoconchids, which occurred abundantly in the shallow seas around South China before the mass extinction event but failed to survive it. Among foraminifera, the extinction event exhibited a strong size-dependent selectivity; large foraminifera suffered especially heavily during the crisis. The Verbeekinidae, a family of large fusuline foraminifera, went extinct. Morphologically complex miliolids also suffered major losses. 87% of brachiopod species found at the Kapp Starostin Formation on Spitsbergen disappeared over a period of tens of thousands of years; though new brachiopod and bivalve species emerged after the extinction, the dominant position of the brachiopods was taken over by the bivalves. The fossil record of East Greenland is similar to that of Spitsbergen; the faunal losses in Canada's Sverdrup Basin are comparable to the extinctions in Spitsbergen and East Greenland, but the post-extinction recovery that happened in Spitsbergen and East Greenland did not occur in the Sverdrup Basin. 87% of brachiopod species and 82% of fusulinacean foraminifer species in South China were lost. The effects of the extinction event on marine vertebrates is enigmatic. There is no evidence of a diversity decline among bony fish, although a pronounced increase in body mass is documented among 'palaeopterygians' across the Guadalupian-Lopingian boundary. Biomarker evidence indicates red algae and photoautotrophic bacteria dominated marine microbial communities. Significant turnovers in microbial ecosystems occurred during the Capitanian mass extinction, though they were smaller in magnitude than those associated with the end-Permian extinction. Most of the marine victims of the extinction were either endemic species of epicontinental seas around Pangaea that died when the seas closed, or were dominant species of the Paleotethys Ocean. Evidence from marine deposits in Japan and Primorye suggests that mid-latitude marine life became affected earlier by the extinction event than marine organisms of the tropics. Whether and to what degree latitude affected the likelihood of taxa to go extinct remains disputed amongst palaeontologists. Whereas some studies conclude that the extinction event was a regional one limited to tropical areas, A study examining foraminiferal extinctions in particular found that the Central and Western Palaeotethys experienced taxonomic losses of a lower magnitude than the Northern and Eastern Palaeotethys, which had the highest extinction magnitude. The same study found that Panthalassa's overall extinction magnitude was similar to that of the Central and Western Palaeotethys, but that it had a high magnitude of extinction of endemic taxa. This mass extinction marked the beginning of the transition between the Palaeozoic and Modern evolutionary faunas. After the Capitanian mass extinction, disaster taxa such as Earlandia and Diplosphaerina became abundant in what is now South China. The initial recovery of reefs consisted of non-metazoan reefs: algal bioherms and algal-sponge reef buildups. This initial recovery interval was followed by an interval of Tubiphytes-dominated reefs, which in turn was followed by a return of metazoan, sponge-dominated reefs. Overall, reef recovery took approximately 2.5 million years. Terrestrial life Terrestrial ecosystems during the leadup to the extinction had relatively high predator to prey ratios, making terrestrial food webs vulnerable to collapse and the extinction strongly felt. Among terrestrial vertebrates, the main victims were dinocephalian therapsids, which were one of the most common elements of tetrapod fauna of the Guadalupian; only one dinocephalian genus survived the Capitanian extinction event. The bolosaurid parareptiles also were completely wiped out. The terrestrial biota of the Karoo after this extinction exhibited very low diversity, with species richness remaining low for up to 3 million years after the main pulse of the mass extinction. The diversity of the anomodonts that lived during the late Guadalupian was cut in half by the Capitanian mass extinction. Terrestrial survivors of the Capitanian extinction event were generally to and commonly found in burrows. Eutherocephalians radiated very rapidly after the extinction event and increased in both disparity and diversity, filling niches left vacant by scylacosaurids and lycosuchids. == Causes ==

Emeishan Traps Volcanic emissions It is believed that the extinction, which coincided with the beginning of a major negative δ13C excursion signifying a severe disturbance of the carbon cycle, basalt piles from which currently cover an area of 250,000 to 500,000 km2, although the original volume of the basalts may have been anywhere from 500,000 km3 to over 1,000,000 km3. Reefs and other marine sediments interbedded among basalt piles indicate Emeishan volcanism initially developed underwater; terrestrial outflows of lava occurred only later in the large igneous province's period of activity. These eruptions would have released high doses of toxic mercury; increased mercury concentrations are coincident with the negative carbon isotope excursion, indicating a common volcanic cause. A large amount of carbon dioxide and sulphur dioxide is believed to have been discharged into the stratosphere of the Northern and Southern Hemispheres due to the equatorial location of the Emeishan Traps, leading to sudden global cooling and global warming. The Emeishan Traps discharged between 130 and 188 teratonnes of carbon dioxide in total, doing so at a rate of between 0.08 and 0.25 gigatonnes of carbon dioxide per year, making them responsible for an increase in atmospheric carbon dioxide that was both one of the largest and one of the most precipitous in the entire geological history of the Earth. Another estimate placed yearly carbon dioxide emissions at .020–.030 gigatonnes per year. Warming during Emeishan eruptions is estimated at 2.3 °C in the first eruption pulse and 1.3 °C in the second eruption pulse. This degree of warming is relatively mild compared to most mass extinctions, as a result of the more drawn-out nature of the eruptions. The Emeishan Traps erupted over the course of two pulses, each lasting about 300,000 years. though this idea has been challenged by studies that instead conclude that the extinction was precipitated directly by the Emeishan Traps or by their interaction with platform carbonates. The emissions of the Emeishan Traps may also have contributed to the downfall of the ozone shield, exposing the Earth's surface to a vastly increased flux of high-frequency solar radiation. The Emeishan Traps were not the only source of volcanic discharges of climate-altering gases; Hg/TOC and Δ199Hg values from strata that were part of the Yangtze Platform indicate that continental arc volcanism also contributed a significant share of emissions and helped cause the biotic crisis. Anoxia and euxinia Global warming resulting from the large igneous province's activity has been implicated as a cause of marine anoxia (oxygen depletion). Emeishan volcanic activity led to two anoxic events, the middle Capitanian OAE-C1 and the end-Capitanian OAE-C2. Volcanic greenhouse gas release and global warming increased continental weathering and mineral erosion, which in turn has been propounded as a factor enhancing oceanic euxinia (excessive hydrogen sulfide alongside oxygen depletion). Euxinia may have been exacerbated even further by the increasing sluggishness of ocean circulation resulting from volcanically driven warming. The initial hydrothermal nature of the Emeishan Traps meant that local marine life around South China would have been especially jeopardised by anoxia due to hyaloclastite development in restricted, fault-bounded basins. Hypercapnia and acidification Because the ocean acts as a carbon sink absorbing atmospheric carbon dioxide, it is likely that the excessive volcanic emissions of carbon dioxide resulted in marine hypercapnia (excessive dissolved carbon dioxide). This would have acted in conjunction with other killing mechanisms to further increase the severity of the biotic crisis. which probably contributed to the demise of various calcareous marine organisms, particularly giant alatoconchid bivalves. By virtue of the greater solubility of carbon dioxide in colder waters, ocean acidification was especially lethal in high latitude waters. Some researchers have cast doubt on whether significant acidification took place globally, concluding that the carbon cycle perturbation was too small to have caused a major worldwide drop in pH. By one estimate, global marine pH dropped by 0.1-0.2 per 300,000 years, about 15 to 35 slower than the pH crisis at the end of the Permian. Analysis of vertebrate extinction rates in the Karoo Basin, specifically the upper Abrahamskraal Formation and lower Teekloof Formation, show that the large scale decrease in terrestrial vertebrate diversity coincided with volcanism in the Emeishan Traps, although robust evidence for a causal relationship between these two events remains elusive. A 2015 study called into question whether the Capitanian mass extinction event was global in nature at all or merely a regional biotic crisis limited to South China and a few other areas, finding no evidence for terrestrial or marine extinctions in eastern Australia linked to the Emeishan Traps or to any proposed extinction triggers invoked to explain the biodiversity drop in low-latitudes of the Northern Hemisphere. with the widespread demise of reefs in particular being linked to this marine regression. Additionally, a tremendous unconformity is associated with the Guadalupian-Lopingian boundary in many strata across the world. The closure of the Sino-Mongolian Seaway at the end of the Capitanian has been invoked as a potential driver of Palaeotethyan biodiversity loss. Other hypotheses Global drying, plate tectonics, and biological competition may have also played a role in the extinction. Potential drivers of extinction proposed as causes of end-Guadalupian reef decline include fluctuations in salinity and tectonic collisions of microcontinents. == See also ==