news center

Fossil fungus reveals human invasion

Fossil fungus reveals human invasion

作者:怀氩  时间:2019-02-26 05:07:01  人气:

By Gaia Vince The fossilised spores of a fungus that thrives in the dung of large mammals has revealed 2000-year-old story of human invasion and environmental devastation in Madagascar. In numerous parts of the world, including Africa, Australia and North America, researchers have seen apparent links between the arrival of humans and the extinction of large animals. But proving humans were to blame, rather than disease for example, has been hard. Now US scientists have used the fossilised spores to shed new light on the ecological catastrophe that befell the world’s fourth largest island. David Burney and colleagues, from Fordham University in New York City, carbon-dated fossil spores of the dung fungus Sporormiella found in sediment cores from throughout Madagascar. They found high levels of the fungal spores across the island up until about 200 AD. This is consistent with paleontological and historical records of large – now extinct – animals inhabiting the island. But during the following two centuries the spore levels dropped to almost zero. Some “remarkable ecological catastrophe eliminated virtually the entire megafauna, including the giant lemurs, elephant birds, pygmy hippopotami and giant tortoises,” the authors write. At about the same time microscopic charcoal appears in the sediments at levels well above the background. This probably signals the arrivals of fire-using humans, they infer. Then, after 900 AD, spore levels began to rise again, suggesting a proliferation of imported livestock. Burney suggests that humans must have arrived at the south-western tip of a island very different to present-day Madagascar – one that was richly forested and populated with large herbivores and flightless birds. In a wave of slaughter and burning, the invaders then appeared to force many species into remote areas of the interior. Some may have survived for as long as a millennium, but eventually, due to habitat destruction, most became extinct. The researchers note that the initial decline in spores occurs before the marked rise in charcoal. They speculate human hunting of the large herbivores would mean the savannah were not as well cropped, leading to more plant material accumulating. This would make fires more common, with humans providing the spark. By this process rich habitats could be turned into spiny bushland and steppe, although the team also acknowledge that an increasingly dry climate may have played a part, Madagascar is mostly scrubland that supports no large animals. The tale told by the fossil spores mirrors an older extinction recorded by eggshells in Australia. A recent study of the shell fragments of an extinct flightless bird called Genyornis suggests human firestarting was to blame for its loss 50,000 years ago. Journal reference: Proceedings of the National Academy of Sciences (DOI: