732 Mammals (Late Quaternary), Extinctions of Critics of anthropogenic models note that kill sites indicating human predation on and processing of allegedly preferred prey are rare, with few in the Americas and none in Australia or Madagascar and few in the Americas The case of Madagascar is especially curious because its losses occurred only within the past 2000 years Skeptics challenge the chronology of extinction, denying that within North America or Australia all extinct large mammals vanished abruptly, on the heels of human colonization, as implied by overkill Some contend that humans arrived in both continents significantly before extinctions occurred If human arrivals triggered megafaunal extinctions in the New World and Australia, critics ask, how we explain the coexistence of Homo sapiens and large mammals in Africa and tropical parts of Eurasia? Vertebrate paleontologists have traditionally appealed to climatic or environmental changes as the main forcing function for many mammalian extinctions During the past 65 million years the vast majority of extinctions occurred before any possibility of human involvement prey for human foragers and predators or be vulnerable (as in the case of minute endemic island snails) to aliens introduced from the continent Although details of how prehistoric humans might have triggered prehistoric extinctions are not easy to interpret from the fossil record, on a global scale the LQEE strongly reflects a deadly syncopation between extinction and human arrival Viewed from the Cenozoic, Alroy (as quoted in MacPhee, 1999, p 105) observed, The event’s timing, rapidity, selectivity, and geographic pattern all make good sense according to the anthropogenic model and no sense at all otherwise I believe that the overkill hypothesis, at least in general terms, already has been ‘‘proven’’ as thoroughly as any historical hypothesis can be See also: Extinction, Causes of Mammals, Biodiversity of Mammals (Pre-Quaternary), Extinctions of Mass Extinctions, Concept of Mass Extinctions, Notable Examples of Climatic Models Climatic models are based on the highly variable nature of late Quaternary environments with rapid switches from cold or cold and dry to warm and wet accompanied by changes in CO2 pressure In some cases, such as the Allerod–Younger Dryas shift within the late glacial, the switch appears to coincide with megafaunal extinctions, especially in North America At least one habitat, the steppe–tundra of polar regions in the Northern Hemisphere, has been identified as an extinct biome (Guthrie as cited in Martin and Klein, 1984) whose end doomed woolly mammoths and other subarctic megafauna Some LQEE models invoke a switch from less extreme to more extreme seasonality with out-of-step breeding cycles eliminating ruminants whose life cycles could not accommodate the climatic changes (Kilte and Graham and Lundelius as cited in Martin and Klein, 1984) Critics discount late Quaternary climatic change as a forcing function since the paleoclimatic record of the Quaternary is rich in rapid and severe changes long before as well as during episodes of extinction Fewer megafaunal extinctions occurred in the 3.5 million years combined, before human arrival, than in the late Quaternary, suggesting that species in Quaternary biotas were buffered against environmental switches typical of the last ice age In any case, a late Quaternary extinction spasm is not evident in the oceans or in freshwater habitats and involves small animals only as parasites or on oceanic islands on which the reduced area would have amplified human impacts Finally, the character of LQEE universally points to species that would either be preferred References Burney DA (1993) Recent animal extinctions: Recipes for disaster Am Sci 81: 530–541 Flannery TF (1994) The Future Eaters Melbourne: Reed Books Goodman S and Patterson B (eds.) 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