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The Quaternary period saw the extinctions of numerous predominantly larger, especially megafaunal, species, many of which occurred during the transition from the Pleistocene to the Holocene epoch. However, this extinction wave did not stop at the end of the Pleistocene, but continued, especially on isolated islands, in Holocene extinctions. Among the main causes hypothesized by paleontologists are natural climate change and overkill by humans, who appeared during the Middle Pleistocene and migrated to many regions of the world during the Late Pleistocene and Holocene. A variant of the latter possibility is the second-order predation hypothesis, which focuses more on the indirect damage caused by overcompetition with nonhuman predators. The spread of disease is also discussed as a possible reason. == The Pleistocene or Ice Age extinction event == The Late Pleistocene extinction event saw the extinction of many mammals weighing more than 40 kg. * In North America around 33 of 45 genera of large mammals became extinct. * In South America 46 of 58 * In Australia 15 of 16 * In Europe 7 of 23 * In Subsaharan Africa only 2 of 44 The extinctions in the Americas entailed the elimination of all the larger (over 100 kg) mammalian species of South American origin, including those that had migrated north in the Great American Interchange. Only in North America, South America, and Australia, did the extinction occur at family taxonomic levels or higher. There are three main hypotheses concerning the Pleistocene extinction: * The animals died off due to climate change associated with the advance and retreat of major ice caps or ice sheets. * The animals were exterminated by humans: the "prehistoric overkill hypothesis" (Martin, 1967).〔Updating Martin's global extinction model. Richard Gillespie. Quaternary Science Reviews. Volume 27, Issues 27–28, December 2008, Pages 2522–2529. Ice Age Refugia and Quaternary Extinctions: An Issue of Quaternary Evolutionary Palaeoecology.〕 * The extinction of the woolly mammoth (by whatever cause, perhaps by humans) changed the extensive grasslands to birch forests, and subsequent forest fires then changed the climate.〔Donald K. Grayson, David J. Meltzer. 2002. Clovis Hunting and Large Mammal Extinction: A Critical Review of the Evidence. Journal of World Prehistory. December 2002, Volume 16, Issue 4, pp 313-359. http://link.springer.com/article/10.1023/A:1022912030020〕 We now know that immediately after the extinction of the mammoth that birch forests replaced the grasslands and that an era of significant fire began.〔Geophysical Research Letters, Vol. 37, L15703, Biophysical feedbacks between the Pleistocene megafauna extinction and climate: The first human-induced global warming? Christopher E. Doughty, Adam Wolf, and Christopher B. Field.〕 There are some inconsistencies between the current available data and the prehistoric overkill hypothesis. For instance, there are ambiguities around the timing of sudden extinctions of Australian megafauna.〔 Biologists note that comparable extinctions have not occurred in Africa and South or Southeast Asia, where the fauna evolved with hominids. Post-glacial megafaunal extinctions in Africa have been spaced over a longer interval. Evidence supporting the prehistoric overkill hypothesis includes the persistence of certain island megafauna for several millennia past the disappearance of their continental cousins. Ground sloths survived on the Antilles long after North and South American ground sloths were extinct. The later disappearance of the island species correlates with the later colonization of these islands by humans. Similarly, dwarf woolly mammoths died out on remote Wrangel Island 1,000 years after their extinction on the mainland. Steller's sea cows also persisted in seas off the isolated and uninhabited Commander Islands for thousands of years after they had vanished from the continental shores of the north Pacific. Alternative hypotheses to the theory of human responsibility include climate change associated with the last glacial period and the Younger Dryas event, as well as Tollmann's hypothetical bolide, which claim that the extinctions resulted from bolide impact(s). Such a scenario has been proposed as a contributing cause of the 1,300 year cold period known as the Younger Dryas stadial. This impact extinction hypothesis is still in debate due to the exacting field techniques required to extract minuscule particles of extra terrestrial impact markers such as Iridium at a high resolution from very thin strata in a repeatable fashion, as is necessary to conclusively distinguish the event peak from the local background level of the marker. The debate seems to be exacerbated by infighting between the Uniformitarianism camp and the Catastrophism camp. 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「Quaternary extinction event」の詳細全文を読む スポンサード リンク
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