At the end of the last ice age, at the same time as the human colonization of the last, farthest-flung regions from Africa, large-bodied mammals (called megafauna) became extinct all over the world. The mass extinctions were neither synchronous nor universal, and the reasons proffered for those extinctions include (but are not limited to) climate change and human intervention.
Before Homo sapiens left Africa to colonize the rest of the world, all of the continents were already populated by a large and diverse animal population, including our hominid cousins Neanderthals and Homo erectus. Animals with body weights greater than 100 pounds (45 kg), called megafauna, were abundant. Extinct elephant, horse, emu, wolves, hippos: the fauna varied with the continent, but most of them were plant eaters, with few predator species. Almost all of these megafauna species are now extinct; most of the extinctions followed the path of Homo sapiens colonization.
The human exodus from Africa and our entrance into the Americas and Australia were also accompanied by climate change. In fact, climate change, migration of humans, extinction of megafauna: evidence indicates that these three events co-occurred over and over again.
Which came first?
Despite what you may have read, it is not clear which of these forces caused the others, and it is very likely that the three forces worked together to re-sculpt the planet. When the planet became colder, vegetation changed, and animals that did not adapt rapidly died out. Climate change may well have driven human migrations; people moving into new territories as new predators might have had negative effects on the existing fauna, through overkill of a particularly easy animal prey, or the spread of new diseases. But, it must be remembered that the loss of the herbivores also drove climate change effects. The loss of large numbers of grass-eating megamammals certainly led or added to the decrease of open vegetation and habitat mosaics, the increased occurrence of fire, and the decline of coevolved plants.
This co-occurrence of humans in migration, climate change, and animal die off is the most recent time in our human history where climate change and human interactions together re-designed the living pallette of our planet. Two areas of our planet are the primary focus of the studies of megafaunal extinctions: North America and Australia, with some studies continuing on South America and Eurasia. All of these areas were subject to massive changes in temperature, including the presence of glacial ice, and plant and animal life; each sustained the arrival of a new predator in the food chain; each saw related decreases and reconfiguration of the available animal and plants. however, evidence collected by archaeologists in each of the areas tells a different story.
- Earliest human colonization: 45,000-50,000 Cal BP ( Lake Mungo)
- Important sites: Darling Downs, Kings Creek, Lynch's Crater (all in Queensland); Mt Cripps and Mowbray Swamp (Tasmania)
- Die off range: 122,000-7.000 years ago; at least 14 Mammalian genera (88%) between 50,000-32,000 cal BP
- Species: reports vary
In Australia, several studies of megafaunal extinctions have been conducted of late, but the results of them are contradictory and conclusions must be considered controversial today. One difficulty with the evidence is that the human entrada into Australia occurred so much longer ago than that of the Americas. Most scholars agree that humans reached the Australian approximately 50,000 years ago; evidence is sparser, and radiocarbon dating ineffective for dates older than 50,000 years old.
According to Gillespie at all, Genyornis newtoni, Zygomaturus, Protemnodon, sthenurine kangaroos and T. carnifex all disappeared at or shortly after human occupation of the Australian mainland. Rule and colleagues report that 20 or more genera of giant marsupials, monotremes, birds, and reptiles were likely wiped out due to direct intervention of human populations, since they can find no connection to climate change. finally, Price and colleagues argue that the local decline in diversity began nearly 75,000 years before human colonization, and thus cannot be the results of human intervention.
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