Humans killed most of Australia’s megafauna: study
Humans likely killed most of Australia’s native megafauna some 45,000 years ago, a new study suggests.
Animals including 450kg kangaroos, 2000kg wombats, 7m-long lizards, 180kg flightless birds, 130kg marsupial lions and car-sized tortoises once roamed the Australian continent. Yet, shortly after the arrival of humans, more than 85 per cent of these critters went extinct, according to Dr Gifford Miller, a professor at the University of Colorado Boulder, and co-author of the new study published in Nature Communications.
In the past decades, scientists have been debating the causes of this massive extinction. Some claim the animals died off due to climatic changes, when most of the Australian landscape shifted to an arid environment.
Other experts think these animals were hunted to extinction by the first Australians, about 50,000 years ago, or a combination of hunting and climate change, says Miller.
New evidence
To address this mystery, a research team from Monash University in Victoria and the University of Colorado Boulder in the USA, drilled sediment cores off the coast of southwest Australia. These cores provide a historical abundance record of things such as dust, pollen, ash and spores, which helped scientists rebuild the ancient climate and ecosystem of the Australian continent for the past 150,000 years.
The team focused its attention on spores from a fungus called Sporormiella that thrived on the faeces of ancient plant-eating animals. Based on the analyses of these sediment cores, researchers were able to determine when these big animals went extinct and whether there were any big climate changes during that period.
“Our study found that the demise of the megafauna in southwest Australia took place from 45,000 to 43,100 years ago and was not linked to major changes in climate, vegetation or biomass burning but is consistent with extinction being driven by ‘imperceptible overkill’ by humans,” said palaeoecologist Dr Sander van der Kaars from the Monash School of Earth, Atmosphere and Environment, who led the study.
“The abundance of these spores is good evidence for a lot of large mammals on the southwestern Australian landscape up until about 45,000 years ago,” he said. “Then, in a window of time lasting just a few thousand years, the megafauna population collapsed,” Miller added.
The researchers also suggest the Australian southwest is one of the few regions in Australia that had dense forests both 45,000 years ago and today, making it a biodiversity hotspot, Miller explained.
“It’s a region with some of the earliest evidence of humans on the continent, and where we would expect a lot of animals to have lived,” he said. “Because of the density of trees and shrubs, it could have been one of their last holdouts some 45,000 years ago. There is no evidence of significant climate change during the time of the megafauna extinction.”
Controversial findings
However, not everyone agrees with this view – suggesting the debate is a long way from over.
“The authors try hard to make the study show evidence that humans wiped out the megafauna, but make a lot of basic mistakes along the way, notwithstanding ignoring and misrepresenting existing datasets. For instance, they state that humans arrived in Australia 47,000 years ago, but ignore the fact that the oldest evidence for the peopling of the continent is around 55,000 years ago,” commented Dr Gilbert Price, a lecturer in palaeontology at the University of Queensland.
“Their reliance of the dung fungus is also problematic, he said.
“The dung fungus is not found exclusively on the dung of large herbivores. The fungus is actually found on the dung of a wide range of different-sized species, from rodents to big animals, plus birds, lizards, and even carnivores,” said Gilbert.
Gilbert added that the presence of Sporormiella spores is nothing more than an indicator of abundance for any animal, whatever its size or diet. He also noted that, being a fungus, climatic factors such as humidity may also influence its abundance.
There is also more direct evidence pointing to a different timeframe for the extinction of these large animals, said Michael Westaway, a Senior Research Fellow at Griffith University who also wasn’t involved in this study.
“Directly dated fauna is much more relevant to the debate than proxies such as spores from off sea cores. We have direct dates for megafauna at 33,000 years ago now, which essentially shows that the overkill idea is not supported from direct dates on fauna,” he said.
Another concern about this new study is that there is no clear evidence of megafauna even being around the region where the core was collected, said Gilbert.
“The closest megafaunal deposits that date to the time range discussed by the authors are over 500 km away. And there, the best evidence shows that there was a progressive decline in megafaunal diversity through time, including prior to the period when humans arrived on the continent!” he adds.
The final verdict is still elusive, said Michael, as current data is just not enough to reach a conclusion. “The debate requires more field research on fossil sites, certainly ecological modelling looks like a bit of fun and proxies such as cores of dung fall in this category as well but against direct dates bracketing the age of fauna they don’t amount to much,” he said.
