FACT SHEETS

People, climate, and water supply all played a role in the extinction of Australia’s megafauna

25.11.19 by By Zoë Taylor

Imagine trying to solve a mystery that is tens of thousands of years old. There are no witnesses still alive, clues are scarce, and even the evidence that does exist is sometimes of questionable reliability.

This has been a challenge facing scientists trying to piece together the factors that led to the extinction of the Australian megafauna, giant beasts wandering across the continent including wombat-like creatures as big as cars, birds more than two metres tall, and lizards more than seven metres long.

Alorchestes azeal, sometimes referred to as the ‘marsupial tapir’ was a cow-sized beast, which probably weighed about 500 kg. Illustration by Gabriel Ugueto.
What factors played a part in the demise of megafauna?
A combination of human pressure and climate change
Piecing together the clues
Data on more than 10,000 fossils were used on the analysis

Clues, in the shape of fossils and archaeological evidence of varying quality scattered across Australia , have formed the basis of several hypotheses about the fate of megafauna and the role of people in their demise around 42,000 years ago.

Now, a combination of collating, and quality-rating more than 10,000 fossil and archaeological records using sophisticated modelling is finally revealing a clearer picture of when and why these fascinating giants stopped roaming the landscape. And the answers are much more complex and regionally diverse than expected.

For the first time, the research suggests a combination of climate change and the impact of people on the environment combined to seal the fate of megafauna. And that configuration of freshwater — a precious commodity for animals and people alike as the climate warmed — can explain regional differences in the timing at which megafauna died out.

Let’s set the scene for this mystery by imagining the landscape during the period known as the Pleistocene — that’s from about 2.6 million years ago to 12,000 years ago. We know the continent was located pretty much where it is today. But sea levels were at times up to 120 metres lower, exposing land bridges to Tasmania in the south and New Guinea in the north. This super-continent , call ‘Sahul’ was at its maximum 50 per cent larger than present-day Australia.

We also know that this was a period of extreme swings in climate, due to the waxing and waning of the polar ice caps. This meant the climate cycled rapidly between cold, dry conditions and shorter periods of relatively warmer, wetter conditions. By the end of the last Ice Age — about 12,000 years ago — the climate became warmer and drier. The resulting loss of habitat for these large browsing animals, likely led megafauna to retreat to a narrow band of eastern Australia where there were permanent water sources and better vegetation.

Let’s set the scene for this mystery by imagining the landscape during the period known as the Pleistocene — that’s from about 2.6 million years ago to 12,000 years ago. We know the continent was located pretty much where it is today. But sea levels were at times up to 120 metres lower, exposing land bridges to Tasmania in the south and New Guinea in the north. This super-continent , call ‘Sahul’ was at its maximum 50 per cent larger than present-day Australia.

We also know that this was a period of extreme swings in climate, due to the waxing and waning of the polar ice caps. This meant the climate cycled rapidly between cold, dry conditions and shorter periods of relatively warmer, wetter conditions. By the end of the last Ice Age — about 12,000 years ago — the climate became warmer and drier. The resulting loss of habitat for these large browsing animals, likely led megafauna to retreat to a narrow band of eastern Australia where there were permanent water sources and better vegetation.

Previous research has suggested that the peak of megafauna extinction took place around 42,000 years ago. With dates for human activity in Sahul as far back as 65,000 years ago, and many Aboriginal cultures believing people have always been here, we know that people and megafauna co-existed.

But there is less certainty about the role that people may have played in the demise of megafauna.

The questions that have perplexed the scientific community include:

Did climate change drive megafauna extinction?

Did people hunt megafauna to extinction?

Were megafauna disadvantaged by changes to the environment caused by people modifying the landscape?

Diprotodon
Genornyis-Newtoni

However, these debates have been contested on the basis of scant evidence.

“The problem is that Australia doesn’t have a great environment for fossil preservation, meaning that our knowledge of the deep history of the extinctions in relation to the climate back then has been rudimentary,” explains researcher Dr Frédérik Saltré, of Flinders University and CABAH Associate Investigator.

“Because of the rarity of good fossil information, evidence has been lumped together across entire landscapes in a bid to answer these questions,” adds Dr Saltré, Research Fellow and Coordinator of the Global Ecology Lab at Flinders University.

But the new study, by Dr Saltré and colleagues at CABAH, have finally compared regional patterns of extinction, with climate change and evidence of people impacting megafauna. The findings, published in Nature Communications, are the result of sophisticated modelling based on data including more than 10,000 fossil and archaeological records.

“By developing a complex mathematical technique to determine both the regional patterns of megafauna disappearances and the migration of people across south-eastern Australia, we could finally compare these properly with patterns of changing climate over the last 120,000 years,” adds Dr Saltré.

Using high-quality fossil data and archaeological evidence of human activity, the researchers were able to map regional patterns of megafauna extinction. They developed sophisticated models to test the impact of factors including climate, water availability and human activity on localised patterns of megafauna extinction.

 

 

 

The analysis revealed that the overlap of megafauna and people varied between 1,000 and 15,000 years in different regions. This variation in the periods of co-existence of people and megafauna suggests that the megafauna’s demise was not entirely due to people being ‘super predators’, the authors conclude.

However, climate change alone could not explain the patterns of extinction either.

The extinction pattern could only be explained by the combination of people sharing the environment and reduction of availability of freshwater due to climate change.

“The regional extinction patterns are best explained by the hypothesis that people migrated across Australia, exploiting lakes and other sources of drinking water connecting the drier regions in between,” the authors say. “It is plausible that megafauna were attracted to the same freshwater sources as were humans, thus increasing the chance of interactions.”

The new insight that human pressure and climate change work together to trigger species extinction is a “stark warning” for the immediate future of the planet’s biodiversity facing even stronger climate and habitat disruption, Dr Saltré concludes.

Play our Accidental Time Traveller game — fight megafauna, brave the elements and test your survival skills in our two-minute mini adventure.

Learn about 10 Giant Critters that once roamed Australia in our interactive explainer.

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