Pleistocene megafauna

Pleistocene megafauna is the set of large animals that lived on Earth during the  and became extinct during the. are any animals with an adult body weight of over 44 kg (97 lbs).

Paleoecology
The, commonly referred to as the 'Ice Age', spanned 125,000 to 14,500 years ago and was the most recent within the  which occurred during the last years of the  epoch. The Ice Age reached its peak during the, when s commenced advancing from 33,000 years 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.

A vast stretched from the Iberian peninsula across Eurasia and over the  into Alaska and the Yukon where it was stopped by the. 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. 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.

The fossil evidence from many continents points to the mainly of large animals at or near the end of the last glaciation. These animals have been termed the Pleistocene megafauna. The most common definition of megafauna is the set of animals with an adult body weight of over 44 kg. Across Eurasia, the became extinct between 100,000–50,000 years BP. The (Ursus spelaeus), interglacial rhinoceros (), heavy-bodied Asian antelope (Spirocerus), and the Eurasian es died out between 50,000-16,000 years BP. The, and  died out between 16,000-11,500 years BP. The died out after 11,500 BP with the last pocket having survived until about 7,700 years BP in western Siberia. A pocket of mammoths survived on until 4,500 years BP. As some species became extinct, so too did their predators. Among the top predators, the sabre-toothed cat () died out 28,000 years BP, the 11,900 years BP, and the  in Europe died out 27,000 years BP. 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, or one population by another within the same species, across a broad area.

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

Theories
Four theories have been advanced as likely causes of these extinctions: by the spreading humans,, spreading , and an impact from an asteroid or comet. These factors are not necessarily exclusive: two or more may have combined to cause the extinctions. Most evidence suggests that humans were a major factor responsible for these extinctions.

North America
During the American megafaunal extinction event around 12,700 years ago, 90 genera of mammals weighing over 44 kilograms became extinct. The  in  included s,, several species of ,  (including the  and  peccaries), the , s, ' ("American cheetahs", not true cheetahs), saber-toothed cats like ' and the scimitar cat, ', , ,  such as two species of now extinct s and ', at least two species of , the , the  and , 14 species of  (of which 13 are now extinct), , s and s, the  and the giant armadillo-like , and  , as well as birds like , other  and. In contrast, today the largest North American land animal is the.

South America
n wildlife in the Pleistocene varied greatly; an example is the giant, . The continent also had quite a few grazers and mixed feeders such as the camel-like ', ', ', ',  ' and '. There were also s, found as far south as. The main predators of the region were ' and '.

Eurasia
As with South America, some elements of the n megafauna were similar to those of North America. Among the most recognizable Eurasian species are the, , , , , , , , ', , , , , , and '. In contrast, today the largest European land mammal is the European bison or.

Africa
evolved here.

Australia
was characterized by s, s, ns,, s and numerous large s. Pleistocene Australia also supported the large (Procoptodon goliah), ' (a giant ), the  (Thylacoleo carnifex), the flightless birds ' and ', the 5-meter  ' and the giant , the.

Insular
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, and the ; giant bird forms in  such as the s and  (a giant eagle); numerous species in : giant lemurs, including ', ' and the gorilla-sized ', , a , the '-crocodile and the gigantic '; various  species from the ; a dwarf ' on  and a number of other islands;  and  in ;   and  in the ; giant geese and  (giant ducks) in ; and s and  from the  islands. The were also inhabited by an endemic megafauna which are now extinct: giant lizards ('), giant rats (' and ') and giant tortoises (' and ), among others.