The Quaternary period (from 2.588 ± 0.005 million years ago to the present) has seen the extinctions of numerous predominantly megafaunal species, which have resulted in a collapse in faunal density and diversity and the extinction of key ecological strata across the globe. The most prominent event in the Late Pleistocene is differentiated from previous Quaternary pulse extinctions by the widespread absence of ecological succession to replace these extinct species, and the regime shift of previously established faunal relationships and habitats as a consequence.

The earliest casualties were incurred at 130,000 BCE (the start of the Late Pleistocene), in Australia ~ 60,000 years ago, in Americas ~ 15,000 years ago, coinciding in time with the early human migrations. However, the great majority of extinctions in Afro-Eurasia and the Americas occurred during the transition from the Pleistocene to the Holocene epoch (13,000 BCE to 8,000 BCE). This extinction wave did not stop at the end of the Pleistocene, continuing, especially on isolated islands, in human-caused extinctions, although there is debate as to whether these should be considered separate events or parts of the same event.

Among the main causes hypothesized by paleontologists are overkill by the widespread appearance of humans and natural climate change. A notable modern human presence first appeared during the Middle Pleistocene in Africa, and started to establish continuous, permanent populations in Eurasia and Australasia from 100,000 BCE and 63,000 BCE respectively, and the Americas from 22,000 BCE.

A variant of the former possibility is the second-order predation hypothesis , which focuses more on the indirect damage caused by overcompetition with nonhuman predators. Recent studies have tended to favor the human-overkill theory

The Late Pleistocene saw the extinction of many mammals weighing more than 40 kg. The proportion of megafauna extinctions is progressively larger the further the human migratory distance from Africa, with the highest extinction rates in Australia, and North and South America.

Extinctions in the Americas eliminated all mammals larger than 100 kg of South American origin, including those which migrated north in the Great American Interchange. It was only in Australia and the Americas that extinction occurred at family taxonomic levels or higher. This may relate to non-African megafauna and Homo sapiens not having evolved as species alongside each other. These continents had no known native species of Hominoidea (apes) at all, so no species of Hominidae (greater apes) or Homo.

The increased extent of extinction mirrors the migration pattern of modern humans: the further away from Africa, the more recently humans inhabited the area, the less time those environments (including its megafauna) had to become accustomed to humans (and vice versa).

There is no evidence of megafaunal extinctions at the height of the Last Glacial Maximum, suggesting that increased cold and glaciation were not factors in the Pleistocene extinction.[18]

There are three main hypotheses to explain this extinction:

• climate change associated with the advance and retreat of major ice caps or ice sheets.
• "prehistoric overkill hypothesis"
• the extinction of the woolly mammoth allowed the extensive grassland to become birch forest, then subsequent forest fires changed the climate.

There are some inconsistencies between the current available data and the prehistoric overkill hypothesis. For instance, there are ambiguities around the timing of sudden Australian megafauna extinctions. Evidence supporting the prehistoric overkill hypothesis includes the persistence of megafauna on some islands for millennia past the disappearance of their continental cousins. For instance, Ground sloths survived on the Antilles long after North and South American ground sloths were extinct, woolly mammoths died out on remote Wrangel Island 1,000 years after their extinction on the mainland, while Steller's sea cows persisted off the isolated and uninhabited Commander Islands for thousands of years after they had vanished from the continental shores of the north Pacific. The later disappearance of these island species correlates with the later colonization of these islands by humans.

Alternative hypotheses to the theory of human responsibility include climate change associated with the last glacial period, and the Younger Dryas impact hypothesis as well as Tollmann's hypothesis that extinctions resulted from bolide impacts.

Recent research indicates that each species responded differently to environmental changes, and no one factor by itself explains the large variety of extinctions. The causes may involve the interplay of climate change, competition between species, unstable population dynamics, and human predation.

The Afrotropic and Indomalaya biogeographic realms, or Old World tropics, were relatively spared by the Late Pleistocene extinctions. Sub-Saharan Africa and southern Asia are the only regions that have terrestrial mammals weighing over 1000 kg today. However, there are indications of megafaunal extinction events throughout the Pleistocene, particularly in Africa two million years ago, which coincide with key stages of human evolution and climatic trends. The center of human evolution and expansion, Africa and Asia were inhabited by advanced hominids by 2mya, with Homo habilis in Africa, and Homo erectus on both continents. By the advent and proliferation of Homo sapiens circa 315,000 BCE, dominant species included Homo heidelbergensis in Africa, the denisovans and neanderthals (fellow H. heidelbergensis descendants) in Eurasia, and Homo erectus in Eastern Asia. Ultimately, on both continents, these groups and other populations of Homo were subsumed by successive radiations of H. sapiens. There is evidence of an early migration event 268,000 BCE and later within neanderthal genetics, however the earliest dating for H. sapiens inhabitation is 118,000 BCE in Arabia, China and Palestine and 71,000 BCE in Indonesia.Additionally, not only have these early Asian migrations left a genetic mark on modern Papuan populations, the oldest known pottery in existence was found in China, dated to 18,000 BCE. Particularly during the late Pleistocene, megafaunal diversity was notably reduced from both these continents, often without being replaced by comparable successor fauna. Climate change has been explored as a prominent cause of extinctions in Southeast Asia.

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