Pleistocene megafauna

Pleistocene megafauna is the set of large animals that lived on Earth during the Pleistocene epoch and became extinct during the Quaternary extinction event. Megafauna are any animals with an adult body weight of over 45 kilograms (99 lb).

Recreation of a scene in late Pleistocene northern Spain, by Mauricio Antón

Paleoecology

The last glacial period, commonly referred to as the 'Ice Age', spanned 125,000[1] to 14,500[2] years ago and was the most recent glacial period within the current ice age which occurred during the final years of the Pleistocene epoch.[1] The Ice Age reached its peak during the last glacial maximum, when ice sheets commenced advancing from 33,000 years BP and reached their maximum positions 26,500 years BP. Deglaciation commenced in the Northern Hemisphere approximately 19,000 years BP, and in Antarctica approximately 14,500 years BP which is consistent with evidence that this was the primary source for an abrupt rise in the sea level 14,500 years ago.[2]

A vast mammoth steppe stretched from the Iberian peninsula across Eurasia and over the Bering land bridge into Alaska and the Yukon where it was stopped by the Wisconsin glaciation. This land bridge existed because more of the planet's water was locked up in glaciation than now and therefore the sea levels were lower. When the sea levels began to rise this bridge was inundated around 11,000 years BP.[3] During the last glacial maximum, the continent of Europe was much colder and drier than it is today, with polar desert in the north and the remainder steppe or tundra. Forest and woodland was almost non-existent, except for isolated pockets in the mountain ranges of southern Europe.[4]

The fossil evidence from many continents points to the extinction mainly of large animals at or near the end of the last glaciation. These animals have been termed the Pleistocene megafauna. Scientists frequently define megafauna as the set of animals with an adult body weight of over 45 kg (or 99 lbs).[5] Across Eurasia, the straight-tusked elephant became extinct between 100,000–50,000 years BP. The cave bear (Ursus spelaeus), interglacial rhinoceros (Stephanorhinus), heavy-bodied Asian antelope (Spirocerus), and the Eurasian hippopotamuses died out between 50,000-16,000 years BP. The woolly rhinoceros and mammoths died out between 16,000-11,500 years BP. The giant deer died out after 11,500 BP with the last pocket having survived until about 7,700 years BP in western Siberia.[6] A pocket of mammoths survived on Wrangel Island until 4,500 years BP.[7] As some species became extinct, so too did their predators. Among the top predators, the sabre-toothed cat (Homotherium) died out 28,000 years BP,[8] the cave lion 11,900 years BP,[9] and the leopard in Europe died out 27,000 years BP.[10] The Late Pleistocene was characterized by a series of severe and rapid climate oscillations with regional temperature changes of up to 16 °C, which has been correlated with megafaunal extinctions. There is no evidence of megafaunal extinctions at the height of the LGM, indicating that increasing cold and glaciation were not factors. Multiple events appear to also involve the rapid replacement of one species by one within the same genus, or one population by another within the same species, across a broad area.[11]

The ancestors of modern humans first appeared in East Africa 195,000 years ago.[12] Some migrated out of Africa 60,000 years ago, with one group reaching Central Asia 50,000 years ago.[13] From there they reached Europe, with human remains dated to 43,000-45,000 years BP discovered in Italy,[14] Britain,[15] and in the European Russian Arctic dated to 40,000 years ago.[16][17] Another group left Central Asia and reached the Yana River, Siberia, well above the Arctic circle, 27,000 years ago.[18] Remains of mammoth that had been hunted by humans 45,000 YBP have been found at Yenisei Bay in the central Siberian Arctic.[19] Modern humans then made their way across the Bering land bridge and into North America between 20,000-11,000 years ago, after the Wisconsin glaciation had retreated but before the Bering land bridge became inundated by the sea.[20] These people then populated the Americas. In the Fertile crescent the first agriculture was developing 11,500 years ago.[21]

Extinction

Four theories have been advanced as likely causes of these extinctions: hunting by the spreading humans (or overkill hypothesis, initially developed by geoscientist Paul S. Martin),[22] the change in climate at the end of the last glacial period, disease, and an impact from an asteroid or comet.[23] These factors are not necessarily exclusive: any or all may have combined to cause the extinctions. Of these, climate change and the overkill hypothesis[24] have the most support,[25] with evidence weighing towards the overkill hypothesis.[26] Although not mutually exclusive, which factor was more important still remains contested.[27][26] Where humans appeared on the scene, megafauna went extinct;[28][29] but at the same time, the climate was also warming. Large body size is an adaptation to colder climes, so a warming climate would have provided a stressor for these large animals; however, many fauna simply evolved a smaller body size over time.[30] There is overwhelming archaeological evidence suggesting humans did indeed hunt some or many of the now extinct species, such as the mammoth in North America;[31] on the other hand, there is not much evidence for this in Australia for most of the megafauna that went extinct there,[24] aside from a large bird.[32] A 2017 study in Nature Communications asserts that humans were the primary driver of the extinction of Australian megafauna.[33] One paper arguing genetic evidence shows there were many species of megafauna that went extinct "invisibly" argues that this means climate change was primarily responsible.[27] Regardless, evidence suggests that humans were a major factor responsible for these extinctions.[26]

Regions affected
See also: Quaternary extinction event

North America
See also: List of North American animals extinct in the Holocene

During the American megafaunal extinction event around 12,700 years ago, 90 genera of mammals weighing over 44 kilograms became extinct.[34][35] The Late Pleistocene fauna in North America included giant sloths, short-faced bears, several species of tapirs, peccaries (including the long-nosed and flat-headed peccaries), the American lion, giant tortoises, Miracinonyx ("American cheetahs", not true cheetahs), the saber-toothed cat Smilodon and the scimitar-toothed cat Homotherium,[36] dire wolves, saiga, camelids such as two species of now-extinct llamas and Camelops,[37] at least two species of bison, the stag-moose, the shrub-ox and Harlan's muskox, 14 species of pronghorn (of which 13 are now extinct), horses, mammoths and mastodons, the beautiful armadillo and the giant armadillo-like Glyptotherium,[38] and giant beavers, as well as birds like giant condors, other teratorns and terror birds. In contrast, today the largest North American land animal is the American bison.[39][40][41]

South America
See also: List of South American animals extinct in the Holocene

South American wildlife in the Pleistocene varied greatly; an example is the giant ground sloth, Megatherium.[42] The continent also had quite a few grazers and mixed feeders such as the camel-like litoptern Macrauchenia, Cuvieronius, Doedicurus, Glyptodon, Hippidion and Toxodon. There were also Stegomastodons, found as far south as Patagonia.[43] The main predators of the region were Arctotherium and Smilodon.

Eurasia
A painting by Heinrich Harder showing an aurochs fighting off a wolf pack

As with South America, some elements of the Eurasian megafauna were similar to those of North America. Among the most recognizable Eurasian species are the woolly mammoth, steppe mammoth, straight-tusked elephant, European hippopotamuses, aurochs, steppe bison, cave lion, cave bear, cave hyena, Homotherium, Irish elk, giant polar bears, woolly rhinoceros, Merck's rhinoceros, narrow-nosed rhinoceros, and Elasmotherium. In contrast, today the largest European land mammal is the European bison or wisent.

By the advent and proliferation of modern humans (Homo sapiens) circa 315,000 BP,[44][45][46] the most common species of the genus Homo in Eurasia were the Denisovans and Neanderthals (fellow H. heidelbergensis descendants), and Homo erectus in Eastern Asia.[47] Homo sapiens is the only species of the genus Homo that remains extant.

Australia
Sir Richard Owen and a Dinornis (moa) skeleton
Main article: Australian megafauna

Australia was characterized by marsupials, monotremes, crocodilians, testudines, monitors and numerous large flightless birds. Pleistocene Australia also supported the giant short-faced kangaroo (Procoptodon goliah), Diprotodon (a giant wombat relative), the marsupial lion (Thylacoleo carnifex), the flightless bird Genyornis, the five-meter long snake Wonambi and the giant monitor lizard Megalania.[48][49]

Insular
Skull of Canariomys bravoi (Tenerife giant rat). It was an endemic species that is now extinct.

Many islands had a unique megafauna that became extinct upon the arrival of humans more recently (over the last few millennia and continuing into recent centuries). These included dwarf woolly mammoths on Wrangel Island, St. Paul Island and the Channel Islands of California;[50] giant birds in New Zealand such as the moas and Hieraaetus moorei (a giant eagle); numerous species in Madagascar: giant ground-dwelling lemurs, including Megaladapis, Palaeopropithecus and the gorilla-sized Archaeoindris, three species of hippopotamuses, two species of giant tortoises, the Voay-crocodile and the giant bird Aepyornis; five species of giant tortoises from the Mascarenes; a dwarf Stegodon on Flores and a number of other islands; land turtles and crocodiles in New Caledonia; giant flightless owls and dwarf ground sloths in the Caribbean;[51][52] giant flightless geese and moa-nalo (giant flightless ducks) in Hawaii; and dwarf elephants and dwarf hippos from the Mediterranean islands. The Canary Islands were also inhabited by an endemic megafauna which are now extinct: giant lizards (Gallotia goliath), giant rats (Canariomys bravoi and Canariomys tamarani)[53] and giant tortoises (Geochelone burchardi and Geochelone vulcanica),[54] among others.

See also

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