Megafauna comprises extremely large animals, including whales, elephants and dinosaurs. Virtually all of these giant animals are now extinct.
Fifteen thousand years ago, the time called the Pleistocene, there existed extremely large animals, including several species of elephant, such as the well known woolly mammoth, the Sabertooth tiger, the giant short-faced bear, the massive dire wolf, and others which resembled present day camels, llamas, horses, cheetahs, sloths, kangaroos, wombats, snakes and lizards. Many of these large (and small) animals disappeared during or before the last Ice Age (Last Glacial Maximum) between 18,000 and 22,000 years ago. This Ice Age resulted in the environment being much drier and in some cases much colder than the present day. It has been suggested that many of the animals disappeared because of climate change; perhaps they were unable to migrate and perished when waterholes dried up during a local drought. Other people have suggested that Aboriginal people hunted megafauna to extinction. Another theory is that one of the doomed species was a keystone species. In this scenario, the extinction of such a species changed the habitat. This change in habitat structure then brought about the extinction of the other species.
Extinction of megafauna is almost a global phenomenon. Most of the world's continents and islands have lost the larger members of their fauna at some time over the last 50,000 years. Africa is the only continent which has not suffered significant extinctions.
Megafauna became extinct up to 50,000 years ago in Australia and New Guinea, around 10,900 years ago in North (and presumably South) America, about 1500 years ago in Madagascar, and between 900 and 600 years ago in New Zealand. This pattern closely follows the current chronology of human expansion around the world.
Megafauna are the biggest and slowest animals in the environment. These kinds of animals are very vulnerable to hunting, but not to climate change. The extinction of megafauna was most extreme in places where humans arrived as already skilled hunters.
The land has been stripped of most of its native megafauna through human influence. In North America, the vanished species of megafauna were hunted to extinction in a continent-wide "blitzkrieg" lasting several centuries by human hunters who had migrated there from Siberia some 15,000 or more years ago.