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Thursday 25 January 2007   

Rapid Roundup: Scientists respond to new research on Nullarbor caves fossil discovery

In a paper published in the Journal Nature today, scientists announce the discovery of what palaeontologists have described as the "find of the century". It included skeletons and bones of animals that lived in the middle Pleistocene period (the time period between approximately 1.8 million and 11,000 years ago) including a complete skeleton of a "Thylacoleo", Australia’s marsupial lion, and eight kangaroo species that are new to science.

If you need a copy of the paper please let us know on (08) 8207 7419 or email us.

A media release from the authors is available on the WA Museum website or by contacting the AusSMC.

The study also has implications for the debate over whether humans were involved in driving the megafauna to extinction 40,000–50,000 years ago. This issue was discussed in a previous paper published by Dr Gavin Prideaux in the journal Geology earlier this month and available by clicking here.

Here Australian and overseas experts comment on the significance of the find. Feel free to use these quotes in your stories or if you would like to interview these or additional experts, call the AusSMC on (08) 8207 7415 or email us.

Dr Gavin Prideaux, palaeontologist, WA Museum. He led the study into the fossil find at the Thylacoleo Caves and is the lead author on the Nature paper this week.

"The 2002 discovery in caves beneath the Nullarbor Plain of pristine skeletons of the extinct marsupial 'lion' and a range of other weird and wonderful beasts from Australia's Ice Age has been described by palaeontologists as the 'find of the century'. We discovered 69 species of mammals, birds and reptiles, including a remarkable eight new species of kangaroo, the most common of which sported unusually large 'brow-ridges'. Three subsequent expeditions produced hundreds of fossils so well-preserved that they constitute a veritable 'Rosetta Stone' for Ice-Age Australia. The find has enabled us to identify cryptic fragments collected from other parts of the continent, and provides the first clear window into the faunal history of arid Australia.

Dating of the fossils established that animals fell into the caves around half-a-million years ago. Surprisingly, we found that the climate at the time was very similar to today, even though the region must have had a more diverse vegetation to support such a high diversity of herbivores. The best explanation for the change is fire. Many trees and shrubs that are restricted today to pockets around the periphery of the Nullarbor are very nutritious and palatable to herbivores, but are highly sensitive to fire. We believe that they were once widespread throughout the region. While they produce no direct evidence to show that humans were responsible for the changed fire regime, their evidence does greatly undermine the support for the idea that aridity wiped out the megafauna of the Nullarbor and elsewhere in Australia."

Professor John Long, Head of Sciences at Museum Victoria. He was Curator of Vertebrate Palaeontology at the Western Australian Museum when he led what he calls “the three arduous expeditions to the caves from 2002 to 2004”.

"The expeditions to the Thylacoleo Caves in the remote Nullarbor Plains district were the most exciting field trips I've ever particpated in during my past 42 years of collecting fossils. To find complete, undamaged skeletons of Australia's largest predatory marsupial, Thylacoleo, was a dream come true, but it got much better when we realised that there was a diverse fauna of many other other long lost megafauna within the cave deposits. The strange new kangaroo with horny protuberances over its eyes* was the first we recognised, then others began turning up.

The fauna is extraordinarily diverse, well dated, and their isotopic studies of the teeth compared with modern marsupials shows clear adaptations in the megafauna to arid climate. This paper therefore denounces climate change as a main force in driving their extinctions. We have only uncovered the tip of a very big iceberg of Australian prehistory that Gavin and his team will be working on for many more years to fully comprehend the true magnitude of the discovery."

* John’s drawing of this horned kangaroo is available by clicking here (Please acknowledge John Long as the artist).

Professor Richard ‘Bert’ Roberts, geochronologist, University of Wollongong. He was part of the geochronology (dating) team, working on the key question of when the animals had fallen into the caves?

"From my perspective, the key result is the remarkable extent to which the animals were supremely well-adapted to dry conditions, and how unlikely it is that climate change could have been the primary 'trigger' for megafaunal extinction in Australia -- an event that took place sometime between 40 and 50 thousand years ago, when the environment was actually less arid than is it today. It was first suggested back in the 1880s that the megafauna had disappeared because the climate became too dry for survival, and this idea has been bounced around ever since as the driving force behind their disappearance. But the Nullarbor discoveries, together with the findings for Naracoorte Caves in South Australia published earlier this month in 'Geology', show convincingly that the Australian megafauna could take all that nature could throw at them for half-a-million years, without succumbing. The megafauna were astonishingly resilient to the vagaries of the Ice Age climates, and it was only when people arrived that they vanished from the landscape. As a species, we could learn a lot about survival from the Australian megafauna, who managed to persist through some of the most arid periods inflicted on the driest inhabited continent on Earth."

Dr Paul Willis, Reporter/Producer, Catalyst. ABC TV. Paul has a doctorate in vertebrate palaeontology and is the co-author of Digging Up Deep Time a history of life as told by Australian fossil deposits.

"Australia has the most distinctive Pleistocene faunas of any continent on earth yet they are also the most poorly understood due to the paucity of high-quality Pleistocene fossil deposits. So when news broke in 2003 of a find on the Nullarbor Plains of a cave filled with complete Pleistocene skeletons, the palaeontological world held its’ breath. There were many unanswered questions that had arisen from more than 150 years of other Pleistocene deposits across the country, perhaps this new site would provide some answers.

Among the most stunning finds was the complete skeleton of the marsupial lion, "Thylacoleo", the first to be found anywhere across the country. The caves had acted as enormous pit-fall traps at least twice during the middle of the Pleistocene, trapping any animal that accidentally fell in. Twenty one of the "megafauna" species found in the caves did not survive to the end of the Pleistocene but, the authors argue, they were all arid adapted and so climate change is unlikely as an agent of their extinction. This could be a useful tool in an on-going debate about the extinction of Australia’s megafauna. Broadly speaking there are two camps. The Blitzkreigers accept an extinction caused by humans arriving in Australia and either hunting the megafauna to extinction or causing other environmental changes that lead to their rapid demise. The other camp argue that changing climate, specifically a period of intense dryness at around 26,000 years before present, was the principle agent of extinction and that humans played little role in pushing a few dozen species of large marsupials over the edge to their doom.

There is enormous promise held in the fossils so far recovered from the caves of the Nullarbor and even further marvels await excavation there. A new window has been opened into our past and new light is being shed on the animals that lived here just prior to humans arriving on the continent. It will take years of study to interpret what that new light has revealed."

Dr John W Magee, Geologist, Department of Earth and Marine Sciences, The Australian National University. He has been actively researching climate and environmental change in arid and semi-arid Australia, since the 1970s.

"The Nullabor Plain, Thylacoleo caves, fossil site reported in Nature by Prideaux et al provides extremely important data for enhancing understanding of the Pleistocene distribution of Australian faunas, their adaptation to arid climates and the late Pleistocene extinction of the Australian megafauna. The Prideaux et al paper provides the first deep-time record of such changes for Australia.

The Thylacoleo Caves record provides cogent evidence that prior to human colonisation of Australia a rich fauna existed, which was well adapted to an arid climate similar to that of today. However, the prevailing ecosystem was substantially different, with a greater floristic complexity and diversity. The authors draw a plausible conclusion that the fundamental change in the ecosystem to the modern fire-resistant chenopod shrub steppe is a likely cause for megafaunal extinctions. This echoes similar conclusions for the extinction of the giant flightless bird Genyornis, by Miller et al in Science, 2005.

While changed fire regimes, probably human-caused, is the most parsimonious explanation for such a change apparently independent of climate, there is little or no direct evidence of fire history from arid and semi-arid Australia. The exciting results reported from the Thylacoleo Caves challenge researchers to unequivocally unravel this crucial segment of Australia’s prehistory."

Jim I. Mead, Professor of Paleontology, Northern Arizona University Flagstaff, Arizona USA.

"Prideaux and his colleagues have discovered and are beginning to assess a natural history treasure trove. Called the Thylacoleo caves, these warehouses of the recent past not only contain an incredibly diverse fauna, but the fossil preservation is without equal on the continent.

The age of these vertebrate assemblages so far assessed by the authors is between 400 and 200 thousand years old. This is a time period just not understood for Australia and the report is incredible and extremely exciting.

Interestingly, the authors indicate that by determining that the recovered vertebrates were adapted to a dry environment, then an extinction hypothesis invoking megafaunal susceptibility to aridity becomes untenable. As they indicate, wildfires played an important part to environmental change, community mosaic alteration. I agree fully.

The authors are to be commended for producing such a detailed, multidisciplinary report about a fauna that is truly unique and is only beginning to release its climatic and biotic record. Clearly the caves contain evidence about a region and time poorly known for Australia. Further field and lab work is desperately desired of these deposits."

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

"Tree kangaroos on the Nullarbor Plain? This new paper shows that only a few hundred thousand years ago the southern arid zone of Australia was home to a rich and diverse assemblage of kangaroos, almost all of which are now extinct. The existence of many species of extinct kangaroos was well known before this study, but very little had been discovered about what species lived in the most arid habitats. Prideaux et al. study shows that many species previously recorded in high-rainfall areas were also present in the arid zone, and these included giant species weighing up to 200 kg. As well, there were smaller and more specialized species so far found nowhere else. The diversity of these kangaroos suggests that the vegetation of the Nullarbor Plain was much more varied at the time than the quite simple shrubland that now covers it. It must have including patches of woodland in which the tree kangaroos lived as well as many different types of food plants to provide a variety of different niches. However, study of the isotope composition of the fossils' teeth show that rainfall was about the same as now.

This study cannot by itself show how the vegetation of this region changed, or why all those kangaroos (and other mammals found with them - a giant wombat and the marsupial lion) went extinct. But what it does make very clear is that until quite recently Australia had many species of large marsupials that were well adapted to arid habitats. The study therefore provides strong evidence against one of the popular theories on the cause of the extinctions. This theory states that Australia's extinct large marsupials were not well-adapted to arid conditions, and gradually disappeared as the continent became drier over the last few hundred thousand years. Prideaux's work adds weight to the alternative view, which is that Australia's giant mammals remained abundant and diverse until the arrival of people about 50-45,000 years ago, and that it was human impact (hunting, or burning of habitat) that caused their extinction."