Pleistocene megafauna
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Pleistocene megafauna were the larger species of mammals, birds and reptiles that lived on earth during the Pleistocene Epoch. These animals suffered a massive extinction event as humanity expanded out of Africa and Eurasia, continents that are the only two still to retain some megafauna equivalent to what was lost. Three competing theories have been given for these extinctions; hunting by the spreading people, climatic change, and spreading disease. Many scientists believe that a combination of these factors may have been responsible.
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[edit] Pleistocene megafauna by region
[edit] Americas
Pleistocene fauna in the Americas included giant sloths, short faced bears, California tapirs, two species of now extinct llamas, peccaries, the American lion, giant condors, Miracinonyx (American "cheetahs", not true cheetahs), saber-toothed cats (like the scimitar cat), dire wolves, camels, at least two species of bison, horses, mammoths and mastodons, and giant beavers. In contrast today the largest North American land mammal is the American Bison. South American megafauna comprised many of the same species as those of North America. Notable species not found in North America include the giant armadillos (Glyptodonts). Other South American large species to go extinct were Toxodonta, and an Elephant like Cuvieronius which lived as late as 400 CE.
[edit] Australia
Australia, then as now, was characterized by marsupials and monotremes. Pleistocene Australia supported large carnivorous kangaroos, Diprotodon (a giant wombat), the Marsupial Lion (Thylacoleo carnifex), the 3-meter flightless bird Dromornis, the 5-meter snake Wonambi and the giant lizard, the megalania.
[edit] Eurasia
As with South America, elements of North American fauna could be found in Eurasia. Among the most famous Eurasian species are the Woolly Mammoth, Aurochs, Cave Lion, Cave Bears, Irish Elk and woolly rhinoceros.
[edit] Insular
Many islands had unique megafauna that went extinct on the arrival of humans. These included giant bird forms in New Zealand such as the moas and the Harpagornis (giant eagle); gorilla-sized lemurs; two species of hippopotamus in Madagascar; dwarf Stegodon from Island of Flores; giant birds, land turtles and crocodiles in New Caledonia; and giant geese and moa-nalos (giant ducks) in Hawaii.
[edit] Extinction
There are three major theories that attempt to explain why these species went extinct so quickly. The possible causes can be summarised as "kill, chill and ill."
[edit] Hunting
The "kill" theory is that Pleistocene humans triggered the megafaunal extinction. This theory has two variants, "blitzkrieg" and "sitzkrieg" or "slow burn." The blitzkrieg theory is that humans hunted the megafauna to extinction in a short time. There is strong evidence of this in several forms. Firstly is the fossil evidence of megafauna found in conjunction with human remains, particularly with evidence of hunting, such as embedded arrows and tool cut marks in the bones, and cave paintings depicting hunting. Secondly is the biogeographical evidence; the areas of the world where humans evolved still have some megafauna (the elephants and rhinos of Asia and Africa) whereas the areas that didn't have early man, Australia, the New World, Madagascar and New Zealand, all lost their megafauna. It is theorised that the megafauna of Asia and Africa evolved with man, and learnt to be wary of them, whereas in other parts of the world the wildlife was ecologically naive and was easier to hunt. This is particularly true of the island fauna. Thirdly, the close correlation between humanity in an area and the extinction of the megafauna in that area also provides weight to the theory of human-caused extinction. The "sitzkrieg" theory is that human encroachment gradually destroyed habitat, and that habitat loss led to a die out.
[edit] Climate change
The "chill" theory explains the extinctions by climatic change following the last Ice Age. Since there were multiple Ice Ages prior to the last one, the climatic theory raises the question, why did the extinctions occur only after the Last Ice Age? One tentative answer is that a nearby supernova altered the galactic environment and as a consequence exaggerated the climatic perturbation. It will require data from space research to advance this claim beyond speculation.
[edit] Disease
The "ill" theory is that a pandemic or hyperdisease caused the megafaunal extinction. According to this theory, large mammals were particularly vulnerable because they were fewer in number than smaller species. Body size and population size tend to be inversely related (because larger species require more food per individual to survive). One suggestion that has been well received, even if it will be difficult to prove, is that pathogens were transmitted by the expanding humans via the domesticated dogs they brought with them. Diseases imported by people have been responsible for extinctions in the recent past; for example, bringing avian malaria to Hawaii has had a major impact on the isolated birds of the island. The researcher McPhee is searching DNA in mammoth remains from Wrangel Island in Siberia. He hopes to find evidence of infection.
[edit] Combined factors
Some experts claim that various combinations of these factors are responsible for the extinctions. For example, while it is certain in the case of the moa and some other species that hunting was primarily responsible, other species may have been 'pushed over the edge' by hunting when they were already struggling due to imported diseases and climate change.
[edit] Megafauna and legend
Throughout history, humans wondered about the large, fossilized teeth and bones they discovered from time to time. During the classical age, the bones of giants were reputed to have been found. In medieval times, fossils were attributed to fantastic beasts such as dragons and unicorns. The Sioux have legends of Thunder Beasts, and the Aztec believed in giants.
With modern tools, paleontologists have reconstructed a world of beasts as amazing as the dragons and unicorns of folklore, including many larger versions of contemporary mammal, reptile and bird families. Scientists and historians, who long dismissed legends of monstrous creatures as merely myths, are beginning to look at these stories in a new light. The sites where the Greeks claimed to find the bones of giants today produce the bones of mammoths. Similar finds have been made in Central America. Since humans coexisted with these animals, some researchers wonder if the beasts might also be remembered in legend. For example the Australian Dreamtime legends refer to the megafaunal species. The mythical Rainbow serpent, source of creation and destruction, may be based on the Wonambi naracoortensis. The hairy manlike Bunyip may be the Diprotodon, filtered through legend. Clearly it is difficult to translate the poetic vocabulary of myth into the technical language of paleontology. In its fossil form, Wonambi naracoortensis does not need the legend to deserve the name "Rainbow Serpent". Its fossils have opalized and now they shimmer in all colors of the spectrum.
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