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The Late Devonian extinction was one of five major extinction events in the history of the Earth's biota. A major extinction, the Kellwasser Event, occurred at the boundary that marks the beginning of the last phase of the Devonian period, the Famennian faunal stage (the Frasnian-Famennian boundary), about 375–360 million years ago.〔Racki, 2005〕〔McGhee, George R., Jr, 1996. The Late Devonian Mass Extinction: the Frasnian/Famennian Crisis (Columbia University Press) ISBN 0-231-07504-9〕 Overall, 19% of all families and 50% of all genera went extinct. A second, distinct mass extinction, the Hangenberg Event, closed the Devonian period.〔Caplan and Bustin, 1999〕 Although it is clear a massive loss of biodiversity occurred in the Later Devonian, the extent of time during which these events took place is uncertain, with estimates ranging from 500,000 to 25 million years, extending from the mid-Givetian to the end-Famennian.〔Stigall, 2011〕 Nor is it clear whether it concerned two sharp mass extinctions or a series of smaller extinctions, though the latest research suggests multiple causes and a series of distinct extinction pulses through an interval of some three million years.〔(Racki, Grzegorz, "Toward understanding of Late Devonian global events: few answers, many questions" GSA Annual meeting, Seattle 2003 (abstract) ); McGhee 1996.〕 Some consider the extinction to be as many as seven distinct events, spread over about 25 million years, with notable extinctions at the ends of the Givetian, Frasnian, and Famennian stages.〔Sole, R. V., and Newman, M., 2002. "Extinctions and Biodiversity in the Fossil Record - Volume Two, The earth system: biological and ecological dimensions of global environment change" pp. 297-391, ''Encyclopedia of Global Environmental Change'' John Wiley & Sons.〕 By the late Devonian, the land had been colonized by plants and insects. In the oceans were massive reefs built by corals and stromatoporoids. Euramerica and Gondwana were beginning to converge into what would become Pangaea. The extinction seems to have only affected marine life. Hard-hit groups include brachiopods, trilobites, and reef-building organisms; the latter almost completely disappeared, with coral reefs only returning upon the evolution of modern corals during the Mesozoic.〔 The causes of these extinctions are unclear. Leading theories include changes in sea level and ocean anoxia, possibly triggered by global cooling or oceanic volcanism. The impact of a comet or another extraterrestrial body has also been suggested.〔Sole, R. V., and Newman, M. (Patterns of extinction and biodiversity in the fossil record )〕 Some statistical analysis suggests the decrease in diversity was caused more by a decrease in speciation than by an increase in extinctions.〔 This might have been caused by invasions of cosmopolitan species, rather than any single event.〔 Surprisingly, jawed vertebrates seem to have been unaffected by the loss of reefs or other aspects of the Kellwasser event, while agnathans were in decline long before the end of the Frasnian.〔Sallan and Coates, 2010〕 ==The Late Devonian world== During the Late Devonian, the continents were arranged differently, with a supercontinent, Gondwana, covering much of the Southern Hemisphere. The continent of Siberia occupied the Northern Hemisphere, while an equatorial continent, Laurussia (formed by the collision of Baltica and Laurentia), was drifting towards Gondwana. The Caledonian mountains were also growing across what is now the Scottish Highlands and Scandinavia, while the Appalachians rose over America; these mountain belts were the equivalent of the Himalaya today. The biota was also very different. Plants, which had been on land in forms similar to mosses, liverworts, and lichens since the Ordovician, had just developed roots, seeds, and water transport systems that allowed them to survive away from places that were constantly wet—and consequently built huge forests on the highlands. Several different clades had developed a shrubby or tree-like habit by the Late Givetian, including the cladoxylalean ferns, lepidosigillarioid lycopsids, and aneurophyte and archaeopterid progymnosperms.〔 Fish were also undergoing a huge radiation, and the first tetrapods, such as ''Tiktaalik'', were beginning to evolve leg-like structures. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Late Devonian extinction」の詳細全文を読む スポンサード リンク
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