Capitanian mass extinction event
[9] The global nature of the Capitanian mass extinction has been called into question by some palaeontologists as a result of some analyses finding it to have affected only low-latitude taxa in the Northern Hemisphere.
[11] Although faunas began recovery immediately after the Capitanian extinction event,[12][13] rebuilding complex trophic structures and refilling guilds,[11] diversity and disparity fell further until the Permian–Triassic boundary.
[18] Some studies have considered it the third or fourth greatest mass extinction in terms of the proportion of marine invertebrate genera lost; a different study found the Capitanian extinction event to be only the ninth worst in terms of taxonomic severity (number of genera lost) but found it to be the fifth worst with regard to its ecological impact (i.e., the degree of taxonomic restructuring within ecosystems or the loss of ecological niches or even entire ecosystems themselves).
Among vertebrates, Day and colleagues suggested a 74–80% loss of generic richness in tetrapods of the Karoo Basin in South Africa,[20] including the extinction of the dinocephalians.
[26] 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.
[38] 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.
[42] It appears to have been particularly selective against shallow-water taxa that relied on photosynthesis or a photosymbiotic relationship;[43] many species with poorly buffered respiratory physiologies also became extinct.
[46][47] 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.
[2] The brachiopod-mollusc transition that characterised the broader shift from the Palaeozoic to Modern evolutionary faunas has been suggested to have had its roots in the Capitanian mass extinction event, although other research has concluded that this may be an illusion created by taphonomic bias in silicified fossil assemblages, with the transition beginning only in the aftermath of the more cataclysmic end-Permian extinction.
[66][67] 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.
[74] Significant quantities of methane released by dikes and sills intruding into coal-rich deposits has been implicated as an additional driver of warming,[75] 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.
[76][77][78] 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.
[83] 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.
[85] 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.
[89] 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.
[90] Not all studies, however, have supported the volcanic warming hypothesis; analysis of δ13C and δ18O values from the tooth apatite of Diictodon feliceps specimens from the Karoo Supergroup shows a positive δ13C excursion and concludes that the end of the Capitanian was marked by massive aridification in the region, although the temperature remained largely the same, suggesting that global climate change did not account for the extinction event.
[91] 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.
[10] The Capitanian mass extinction has been attributed to sea level fall,[93] with the widespread demise of reefs in particular being linked to this marine regression.
[5] Evidence for abrupt sea level fall at the terminus of the Guadalupian comes from evaporites and terrestrial facies overlying marine carbonate deposits across the Guadalupian-Lopingian transition.
[5][22][48][91] Potential drivers of extinction proposed as causes of end-Guadalupian reef decline include fluctuations in salinity and tectonic collisions of microcontinents.
