Quaternary extinction event

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).[1]
 * 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.[2] 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.[3]

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.[1] 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.[4]

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.[citation needed] 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.[citation needed] The debate seems to be exacerbated by infighting between the Uniformitarianism camp and the Catastrophism camp.[

Africa and Asia
The Old World tropics have been relatively spared by Pleistocene extinctions. Africa and southern Asia are the only regions that have terrestrial mammals weighing over 1000 kg today. However, during the early, middle and late Pleistocene some large animal forms disappeared from these regions without being replaced by comparable successor species. Climate change has been cited as most likely causing the extinctions in Southeast Asia.

Large animals which disappeared in Africa or Asia during the Early and Middle and Late Pleistocene include:
 * Giraffids, including Sivatherium.
 * A species of wolf (Xenocyon lycaonoides)
 * A few species of warthog such as ''Metridiochoerus
 * Chalicotheres
 * Deinotherium, Anancus and Mammuthus subplanifrons, relatives of the elephant
 * Hippopotamus gorgops (a giant hippopotamus)
 * False saber-toothed cats like Dinofelis
 * Giant predatory bear Agriotherium
 * African bear Agriotherium africanum
 * Saber-toothed cats like Megantereon and Homotherium
 * Giant tapir Megatapirus
 * Giant ape Gigantopithecus
 * Giant hyena Pachycrocuta

Large animals, which disappeared in parts of Africa and Asia during the Late Pleistocene: ===Australia and New Guinea The sudden spate of extinctions occurred earlier than in the Americas. Most evidence points to the period immediately after the first arrival of humans—thought to be a little under 50,000 years ago—but scientific argument continues as to the exact date range. The Australian extinctions included:
 * Giant long-horned buffalo (Pelorovis)
 * Giant hartebeest Megalotragus
 * Elephas recki (a species of elephant)
 * Loxodonta adaurora (a species of African elephant)
 * Diprotodon (giant relatives of the wombats)
 * Zygomaturus (a "marsupial rhino")
 * Hulitherium (a large marsupial herbivore)
 * Phascolonus (a giant wombat)
 * Palorchestes azael (a marsupial "tapir")
 * Macropus titan (a giant kangaroo)
 * Procoptodon goliah (a hoof-toed giant short-faced kangaroo)
 * Sthenurus (a giant kangaroo)
 * Simosthenurus (a giant kangaroo)
 * Protemnodon (a giant kangaroo)
 * Propleopus oscillans (an omnivorous kangaroo)
 * Wonambi (a five-to-six-metre-long Australian constrictor snake)
 * Thylacoleo carnifex (a lioness-sized marsupial carnivore)
 * Varanus priscus (or Megalania prisca) (a giant predatory monitor lizard)
 * Quinkana (a five-to-six metre-long predatory terrestrial crocodile)
 * Dromornithidae (The entire family of giant birds. Though around the size of emus, they are actually more related to ducks and other waterfowl.)

Some extinct megafauna, such as the bunyip-like Diprotodon, may be the sources of ancient cryptozoological legends.

Northern Eurasia
(80,000–4,000 years ago)
 * Woolly mammoth (Mammuthus primigenius)
 * Woolly rhinoceros (Coelodonta antiquitatis)
 * Irish elk (Megaloceros giganteus)
 * Scimitar cat (Homotherium sp.)
 * Giant polar bear (Ursus maritimus tyrannus)
 * Cave lion (Panthera leo spelaea)
 * Cave bear (Ursus spelaeus)
 * Cave hyena (Crocuta crocuta spelaea)
 * Steppe wisent (Bison priscus)
 * Elephants (Palaeoloxodon)
 * Elasmotherium (Elasmotherium sibiricum)
 * Merk's rhinoceros (Stephanorhinus kirchbergensis)
 * European hippopotamus (Hippopotamus antiquus)
 * Etruscan bear (Ursus etruscus), ancestor to both the cave bear and brown bear, survived until 11,000 years ago along the Mediterranean coast.
 * Neanderthals (Homo neanderthalensis), survived until about 24,000 years ago in the Iberian peninsula

North America
During the last 60,000 years, including the end of the last glacial period, approximately 33 genera of large mammals have become extinct in North America. Of these, 15 genera extinctions can be reliably attributed to a brief interval of 11,500 to 10,000 radiocarbon years before present, shortly following the arrival of the Clovis people in North America. Most other extinctions are poorly constrained in time, though some definitely occurred outside of this narrow interval.[7] In contrast, only about half a dozen small mammals disappeared during this time. Previous North American extinction pulses had occurred at the end of glaciations, but not with such an ecological imbalance between large mammals and small ones. (Moreover, previous extinction pulses were not comparable to the Quaternary extinction event; they involved primarily species replacements within ecological niches, while the latter event resulted in many ecological niches being left unoccupied.) The megafaunal extinctions include twelve genera of herbivores (H), and five carnivores (C). North American extinctions included:
 * American horses, (Equus, three to five species) (H)
 * Hagerman horse (Equus simplicidens) (H)
 * Mexican horse (Equus conversidens) (H)
 * Scott's horse (Equus scotti) (H)
 * Stilt-legged horse (Equus francisci) (may be synonym of Mexican horse) (H)
 * Yukon wild ass (Equus lambei) (H)

The survivors are in some ways as significant as the losses: bison (H), moose (H) (a late Pleistocene immigrant through Beringia), elk (H), grey wolf (C), caribou (H), grizzly bear (C), American black bear (C), deer (H), pronghorn (H), muskox (H), bighorn sheep (H), and mountain goat (H). All save the pronghorns descended from Asian ancestors that had evolved with human predators.[8] Pronghorns are the second fastest land mammal (after the cheetah), which may have helped them elude hunters. More difficult to explain in the context of overkill is the survival of bison, since these animals first appeared in North America less than 240,000 years ago [9][10][11] and so were geographically removed from human predators for a sizeable period of time. Because ancient bison evolved into living bison,[12][13] there was no continent-wide extinction of bison at the end of the Pleistocene (although the genus was regionally extirpated in many areas). The survival of bison into the Holocene and recent times is therefore inconsistent with the overkill scenario. By the end of the Pleistocene, when humans first entered North America, these large animals had been geographically separated from human hunters for more than 200,000 years. Given this enormous span of geologic time, bison would almost certainly have been very nearly as naive as native North American large mammals.
 * California tapirs (Tapirus californicus and Tapirus merriami) (H)
 * Vero tapir (Tapirus veroensis) (H)
 * Western camel (Camelops hesternus) (H)
 * North American llamas (Hemiauchenia)(H)
 * Deer (Cervidae, two genera) (H)
 * Pronghorn (Antilocapridae, two genera, one survived) (H)
 * Stag-moose (Cervalces scotti) (H)
 * Shrub-ox and Harlan's muskox (the Arctic Muskox survived) (H)
 * Ancient bison (Bison antiquus) (H)
 * Long-horned bison / giant bison (Bison latifrons) (H)
 * Giant beaver (Castoroides, two species) (H)
 * Saiga (Saiga tatarica) (H)
 * Teratorns (C)
 * Pinckney's capybara (Neochoerus pinckneyi) (H)
 * Eremotherium and Nothrotheriops, megatheriid ground sloths (H)
 * Megalonyx, a megalonychid ground sloth (H)
 * Paramylodon, a mylodontid ground sloth (H)
 * Glyptodonts (H)
 * Pampatheres (H)
 * Short-faced bear (Arctodus simus, larger than the present grizzly bear) (C)
 * Florida cave bear (Tremarctos floridanus) (C)
 * Saber-toothed cat (Smilodon fatalis) (C)
 * Scimitar cat (Homotherium serum) (C)
 * Giant polar bear (Ursus maritimus tyrannus, it is possible that this giant relative of the modern polar bear lived in North America) (C)
 * American lion (Panthera leo atrox, larger than the current African lion but probably a fairly recent immigrant through Beringia) (C)
 * American cheetah (Miracinonyx, not a true cheetah, possibly ancestral) (C)
 * Dire wolf (Canis dirus) (C)
 * Mammoth (Mammuthus), several species (H)
 * American mastodon (Mammut americanum) (H)
 * Flat-headed (Platygonus) and long-nosed (Mylohyus) peccaries (H)

The culture that has been connected with the wave of extinctions in North America is the paleo-Indian culture associated with the Clovis people (q.v.), who were thought to use spear throwers to kill large animals. The chief criticism of the "prehistoric overkill hypothesis" has been that the human population at the time was too small and/or not sufficiently widespread geographically to have been capable of such ecologically significant impacts. This criticism does not mean that climate change scenarios explaining the extinction are automatically to be preferred by default, however, any more than weaknesses in climate change arguments can be taken as supporting overkill. Some form of a combination of both factors could be plausible, and overkill would be a lot easier to achieve large-scale extinction with an already dying population due to climate change.

Lack of tameable megafauna was perhaps one of the reasons why Amerindian civilizations evolved differently from Old World ones.[14] Critics have disputed this by arguing that llamas, alpacas, and bison were domesticated.

South America
South America had been isolated, an island continent, for many millions of years, and it had a wide range of mammals found nowhere else, though many of them became extinct during the Great American Interchange about 3 million years ago. Those that survived the interchange included the ground sloths, glyptodonts, pampatheres, and notoungulates; and of these all but the notoungulates extended their range to North America. In the Pleistocene, South America remained largely unglaciated except for increased mountain glaciation in the Andes, and the megafauna were little affected. At the start of the Holocene, the megafauna all became extinct. Their smaller relatives remain, including anteaters, tree sloths, armadillos; New World marsupials: opossums, shrew opossums, and the monito del monte (actually more related to Australian marsupials). Today the largest land mammals remaining in South America are the wild camels of the Lamini group: guanacos and vicuñas and their domestic counterparts llamas and alpacas. Other notable surviving large fauna are tapirs, rheas, jaguars, boa constrictors, anacondas, caymans, and giant rodents like capybaras.
 * Smilodon fatalis and populator
 * Arctotherium
 * Ground sloths of three families
 * Glyptodonts
 * Pampatheres
 * Hippidion
 * Horse (Equus)
 * Toxodon
 * Macrauchenia
 * Cuvieronius
 * Stegomastodon

Mediterranean Islands

 * Pygmy hippos of Cyprus (Phanourios minutus), Crete (Hippopotamus creutzburgi), Malta (H. melitensis) and Sicily (H. pentlandi)
 * Balearic Islands cave goat (Myotragus balearicus) of Majorca and Minorca
 * Dwarf elephants of Cyprus (Elephas cypriotes), Sicily, Malta (E. falconeri) and many other islands
 * Giant swan (Cygnus falconeri) of Malta
 * Giant dormice: Minorcan giant dormouse, Majorcan giant dormouse
 * Sardinian pika of Sardinia and Corsica

New Zealand
c. AD 1500, several species became extinct after Polynesian settlers arrived, including:
 * Moa, giant flightless ratite birds, ten species
 * Haast's eagle (Harpagornis moorei)
 * Adzebills, giant flightless predatory birds, two species
 * Finsch's duck, a large, flightless duck

Pacific, including Hawaii
Recent research, based on archaeological and paleontological digs on 70 different islands, has shown that numerous species became extinct as people moved across the Pacific, starting 30,000 years ago in the Bismarck Archipelago and Solomon Islands (Steadman & Martin 2003). It is currently estimated that among the bird species of the Pacific some 2000 species have gone extinct since the arrival of humans (Steadman 1995). Among the extinctions were:
 * Moa-nalos, giant grazing Hawaiian ducks
 * Nēnē-nui, or woodwalking goose, a large species of goose that once inhabited island of Maui
 * Sylviornis, a giant galliform bird on New Caledonia
 * Mekosuchine crocodiles on New Caledonia, Fiji and Samoa
 * Meiolaniid turtles on Lord Howe Island and New Caledonia
 * "Gavialis" papuensis, a marine crocodilian from the Solomon Islands.

Madagascar
Starting with the arrival of humans c. 2,000 years ago, nearly all of the island's megafauna became extinct, including:
 * Eight or more species of elephant birds, giant flightless ratites in the genera Aepyornis and Mullerornis.
 * 17 species of subfossil lemur, including:
 * Giant aye-aye (Daubentonia robusta)
 * Sloth lemurs, including chimpanzee-sized Palaeopropithecus and gorilla-sized Archaeoindris
 * Pachylemur, a larger, more robust relative of the ruffed lemurs
 * Monkey lemurs (Archaeolemuridae, the most terrestrial of all the known lemurs, often compared to baboons)
 * Megaladapis, an orangutan-sized arboreal lemur similar to a koala
 * Giant tortoise
 * Voay, a terrestrial giant dwarf crocodile
 * Malagasy hippopotamus, three species
 * Plesiorycteropus (an aardvark-like mammal, two species)
 * Giant fossa (Cryptoprocta spelea, a cougar-sized relative of the fossa)
 * Malagasy crowned eagle (Stephanoaetus mahery, a giant bird of prey)

Indian Ocean Islands
Starting c. 500 years ago, a number of species became extinct upon human settlement of the islands, including:
 * Several species of giant tortoise on the Seychelles and Mascarene Islands
 * Many species of birds on the Mascarene Islands, including the dodo, the Rodrigues solitaire, and the unrelated Réunion solitaire.
 * Aldabrachampsus on Aldabra Atoll

Caribbean

 * Giant hutias
 * Cuban coney
 * Brotomys
 * Cuban giant owl