Humans may have played a significant role in the extinction of Australia’s prehistoric giant animals, suggests a new study published in the journal Science.
New evidence obtained by analysing a 130,000-year time sequence of sediments from Lynch’s Crater in north-east Queensland suggests that the megafauna – which included cow-sized browsing marsupials, giant kangaroos and a massive goanna – rapidly declined in numbers about 40,000 years ago, soon after people are thought to have first arrived in the region.
The study was led by Susan Rule, of the Australian National University , with researchers from the University of Tasmania, University of Adelaide, University of New South Wales and Monash University.
UNSW’s Professor Chris Turney led the age-modelling component of the study: he says it offers new insights into the long-running scientific debate about the relative roles humans and environmental change in the extinction of the megafauna.
“The crucial thing is that dating the demise of the magnificent megafauna is terribly difficult given the great antiquity and the coincidence with human arrival in Australia,” Professor Turney says.
“At over 40,000 years ago, it's hard to demonstrate which happened first. Excitingly, in this study - regardless of the differences in the absolute ages - we have a sedimentary record from tropical Queensland that preserves measures of different environmental changes. This allows us to test what happened first.
“Importantly, the sediments preserve the spore of a fungus that grows in herbivore dung and crucially this shows a long-term decline around 40,000 years ago. In this study, we find the fungus drops away before other environmental changes that could be interpreted as drying took place, implying humans played a significant role in the cause of Australian megafaunal extinction.
“Although not the definitive answer, this provides a new insight into the complex changes that were happening in the Australian landscape all those years ago.”
Professor Ross Johnson of the University of Tasmania notes that lakes and swamps preserve spores of specialised fungi that live in the dung of large herbivores: “As those sediments accumulate over time, they create a historical record of the abundance of very large herbivores in the environment. Pollen and charcoal particles are trapped in the same sediments, so that it is possible to match up the history of abundance of large herbivores with changes in vegetation and fire.”
Professor Johnson says the study rules out climate change as a cause of extinction. Several periods of climate drying before the extinction had no effect on the abundance of megafauna and the climate was stable when the animals went extinct. He says the results also suggest that major ecological change were followed quickly after the extinctions, with a shift from rainforest patches and open grassland to widespread eucalypt forest.