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Monday 11 August 2008

RAPID ROUNDUP: New study implicates humans in Australian prehistoric animal extinctions – Experts respond

Under strict embargo until Tuesday 12 August at 7am Australian EST

Rapid Roundup | Online Briefing

Australian research sheds new light on the role that our ancestors played in the extinction of Australia’s large prehistoric animals. There has been ongoing debate about whether climate change or human arrival was the major cause of the demise of Australia’s megafauna. On the Australian mainland, 90% of these animals became extinct soon after the first evidence of the arrival of humans, around 46 thousand years ago. Yet on Tasmania, their extinction is thought to have taken place before the arrival of humans, making climate change the most likely culprit.

A new study, published in the journal Proceedings of the National Academy of Sciences of the USA, provides the first evidence that Tasmania’s large prehistoric animals were still roaming the island when humans first arrived. The findings suggest that their mass extinction was the result of human hunting, and not climate change—as previously believed. Here, Australian experts comment on these new findings.

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Professor Barry Brook is Sir Hubert Wilkins Professor of Climate Change and Director, Research Institute for Climate Change and Sustainability at the University of Adelaide

“This latest study of the persistence dates of Australian megafauna reinforces the maturing view in the science community that the ancient extinction of large mammals were consistently coincident with human arrival. Indeed, each apparently discrepancy, which has seemingly showed a long-term co-existence between prehistoric people and large-bodied mammals, are one-by-one being swept aside, thanks to new dating methods and improved site-profiling. The picture is becoming clear. Whodunnit? Wedunnit.“

Professor Christopher Johnson, Ecologist, School of Tropical Biology, James Cook University. He published a book on mammal extinctions in Australia, called "Australia's Mammal Extinctions: a 50,000 Year History" in 2006.

“This is a big step towards resolution of a very long argument. The evidence that humans caused the extinction of giant ice age mammals in Australia, by over-hunting them, is now much stronger. This study shows that alternative explanations (to do with climate change or fire) won't work in Tasmania. On the other hand, the big picture that is now much clearer is that when people arrive, other big animals disappear. This is a sad and, it seems, almost inevitable feature of our species' impact on nature.”

Dr Richard Cosgrove is a Reader in Archaeology in the Archaeology Program at La Trobe University

"This paper suffers from a number of problems, particularly that there is no temporal overlap, and therefore human involvement in megafauna extinction cannot be unequivocally demonstrated from the data presented in the paper. Turney et al’s argument relies on supposition and assumptions about the timing of human entry across the land bridge, is weakened by small sample sizes, including only one species that actually dates to anywhere near the earliest evidence for human occupation and suggests that the archaeological evidence is too weak to detect human megafaunal hunting. There is the selective use of data in the paper, and as it stands, does not address the over-whelming archaeological evidence that preserves one of the best and most detailed late Pleistocene faunal records associated with human hunting anywhere in the world and to ignore this detracts from the very question of human environmental impacts the paper struggles to address. To ignore the archaeological evidence continues to push the 'faith' based human extinction argument of palaeontologists and geochronologists where no direct evidence exists."

Dr Richard Gillespie is a radiocarbon dating specialist and Visiting Fellow at the University of Wollongong and the Australian National University.

“Did the Australian megafauna (giant marsupials, birds and reptiles) become extinct before or after humans first arrived in Tasmania? New results suggest the answer is after. Geological evidence of sea level change shows that a landbridge emerged between mainland Australia and Tasmania about 43,000 years ago, and people must have walked across pretty soon after it became possible because the oldest archaeological sites in Tasmania date to 40,000 years ago.

Archaeologists have found no extinct animal remains among the many thousands of bones excavated from occupation sites, arguing the giant fauna must have been extinct before people got to Tasmania. Turney and colleagues refute that theory with the first reliable radiocarbon dates on any of the Australian megafauna, showing that an extinct giant kangaroo (Protemnodon anak) lived at Mt Cripps in north western Tasmania 41,000 years ago. More dates are needed to confirm these results, which imply that people and extinct megafauna did coexist in Tasmania, if only briefly.

On mainland Australia, hunting by the first human arrivals most likely caused the megafauna extinction about 45,000 years ago, as they did in America 13,000 years ago, Madagascar 2000 years ago, and New Zealand 600 years ago. The only common factor in the global megafauna extinction pattern is that humans first turned up in those places just before the extinctions happened. Supporters of the rival theory, that climate change killed off the megafauna, have run out of places to hide.”

Dr Judith Field is a Senior Research Associate in Microscopy and Archaeology at the University of Sydney.

“Investigations into the timing and cause of the megafaunal extinctions in Australia is hampered by the small datasets with which to evaluate the fossil record. This report attempts to improve our understanding of the timing of the extinction in Tasmania by directly dating a number of specimens, mostly from museum collections and also dating sediments from some cave sites. The authors assert in this paper that humans were involved in the demise and extinction of the Tasmanian megafauna, a belief based on a set of unproven assumptions and radiocarbon dates from one species.

Significantly for this site (and all of the sites they analyse), the all important evidence of a human presence is absent. A short temporal overlap of all Tasmanian megafauna with humans is proposed on the basis of this result and the unproven assumption that OSL dates from sediments in another site, actually date the fauna. This is extrapolated into ‘human involvement in the megafaunal extinctions’. The dismissal of the archaeology based on there being only 0.6% of faunal material in this time period (and without megafauna), neglects to cite that there are over 800,000 bones that have been examined from the Tasmanian archaeological sites.

Their interpretations and discussion are hampered by the belief that they don’t require contextual data - that dates are all they need. Furthermore their inconsistent use of (a dubious) criterion they propose elsewhere as demonstrating in situ assemblages of bones (i.e. articulated skeletons), undermines this case and the case they make for the Australian mainland. To believe that in the absence of any comparative data or supporting evidence that this new report solves the mystery of why megafauna disappeared in Tasmania grossly overstates their case and extends their interpretation into the realms of speculative fantasy. Whether arguing for human or climatic influences as primary agents in megafaunal extinction, researchers must place their results into some sort of site context and demonstrate associations or interactions of megafauna and humans with empirical evidence. Until or unless this happens it remains premature to claim a human role in the demise of the Australian megafauna, especially when humans cannot even be placed at the scene!”

Gavin Prideaux is a palaeontologist and Australian Research Fellow in the School of Biological Sciences at Flinders University

“Tasmania has been a bit of a ‘fly in the ointment’ for those who have argued that Australia’s giant mammals were driven to extinction by humans. The small amount of available evidence seemed to suggest the megafauna disappeared well before people reached the island. Turney and colleagues now show that at least one, and possibly as many as seven species did in fact survive until humans arrival.”