What killed off the giant beasts, climate change or man?

By Robin McKie for The Guardian,

Earth’s ‘megafauna’ vanished as tribes spread. Now palaeontologists are asking if early humans were the cause

Humans might have played a role in the extinction of the woolly mammoth. Photograph: Andrew Nelmerm/Getty Images/Dorling Kindersley

They were some of the strangest animals to walk the Earth: wombats as big as hippos, sloths larger than bears, four-tusked elephants, and an armadillo that would have dwarfed a VW Beetle. They flourished for millions of years, then vanished from our planet just as humans emerged from their African homeland.

It is one of palaeontology’s most intriguing mysteries and formed the core of a conference at Oxford University las 20th of march when delegates debated whether climate change or human hunters killed off the planet’s lost megafauna, as these extinct giants are known.

“Creatures like megatherium, the giant sloth, and the glyptodon, a car-sized species of armadillo, disappeared in North and South America about 10,000 years ago, when there were major changes to climates – which some scientists believe triggered their extinctions,” said Yadvinder Malhi, professor of ecosystem science at Oxford, one of the organisers of the conference, Megafauna and Ecosystem Function.

“However, it is also the case that tribes of modern humans were moving into these creatures’ territories at these times – and many of us believe it is too much of a coincidence that this happened just as these animals vanished. These creatures had endured millions of years of climate change before then, after all. However, this was the first time they had encountered humans.”

Modern humans emerged from Africa around 70,000 years ago, travelled across Asia and reached Australia 50,000 years ago, a time that coincides with a wave of extinctions of creatures there, including the diprotodon, a species of wombat that grew to the size of a modern hippopotamus. By about 14,000 years ago, humans had reached North America by crossing the land bridge that then linked Siberia and Alaska. Then they headed south.

By 10,000 years ago, Homo sapiens had conquered North and South America at a time that coincided with major megafauna extinctions, including those of the giant sloth and the glyptodon.

“We think of Africa and south-east Asia – with their lions, elephants and rhinos – as the main home of large animals today, but until very recently in our planet’s history, huge creatures thrived in Australia, North America and South America as well,” said Professor Adrian Lister of the Natural History Museum in London. “The question is: why did they disappear in the new world but survive in the old world?

“Some believe it is because large animals in Africa and south-east Asia learned to become wary of human beings and decided to avoid them at all costs. However, I also think climate change may have been involved in the Americas and Australia and that humans only finished off these big animals when they were already weakened by loss of habitats and other climate-related problems.”

The idea that humans were involved in any way in eradicating dozens of species of giant animal when we were still hunter-gatherers has important implications in any case. It was thought, until relatively recently, that it was only when humans invented agriculture several thousand years ago that our species’ relationship with the natural world become unbalanced. Until then, humans had a close affinity with nature. But if ancient hunter-gatherers played a part in wiping out these species of huge animals as long as 50,000 years ago, humanity’s supposed innate harmony with the living world appears misplaced.

More to the point, humanity is still paying the price for the disappearance of the megafauna of the Americas and Australia, the Oxford conference will hear. “There is now a lot of evidence to suggest that large herbivores like gomphotheres, a family of elephant-like animals that went extinct in South America around 9,000 years, played a key role in spreading nutrition in areas like the Amazon. They would eat fruit in the forest, including avocados, and their excrement would then fertilise other areas. That no longer happens and places like the Amazon are today affected by low nutrition as a result,” Malhi said.

Another example is provided by the giant wombat, the diprotodon, which some scientists have argued browsed bush across Australia and kept biomass levels very low. When the diprotodon vanished, plants and shrubs across the outback grew unhindered. The result was major bush fires which, archaeologists have discovered, became a serious problem just after the giant wombat disappeared from Australia.

Woolly mammoth DNA may lead to a resurrection of the ancient beast

Technical and ethical challenges abound after first hurdle of taking cells from millennia-old bodies is cleared

Even a well-preserved carcass like this baby woolly mammoth is unlikely to provide viable cells for cloning, as used to create Dolly. Photograph: Aaron Tam/Getty

By Ian Wilmut

It is unlikely that a mammoth could be cloned in the way we created Dolly the sheep, as has been proposed following the discovery of mammoth bones in northern Siberia. However, the idea prompts us to consider the feasibility of other avenues. Even if the Dolly method is not possible, there are other ways in which it would be biologically interesting to work with viable mammoth cells if they can be found.

In order for a Dolly-like clone to be born it is necessary to have females of a closely related species to provide unfertilised eggs, and, if cloned embryos are produced, to carry the pregnancies. Cloning depends on having two cells. One is an egg recovered from an animal around the time when usually she would be mated.

In reality there would be a need for not just one, but several hundred or even several thousand eggs to allow an opportunity to optimise the cloning techniques. The cloning procedure is very inefficient. After all, after several years of research with sheep eggs, Dolly was the only one to develop from 277 cloned embryos. In species in which research has continued, the typical success rate is still only around 5% at best.

Elephant eggs

Photo: Rubén Portas

In this case the suggestion is to use eggs from elephants. Because there is a danger of elephants becoming extinct it is clearly not appropriate to try to obtain 500 eggs from elephants. But there is an alternative.

There is a considerable similarity in the mechanisms that regulate function of the ovaries in different mammals. It has been shown that maturation of elephant eggs is stimulated if ovarian tissue from elephants is transplanted into mice.

In this way it might be possible to obtain a considerable number of elephant eggs over a period of time if ovarian tissue is obtained from elephants that die.

Cells from mammoths are required to provide the genetic information to control development. The suggestion is to recover cells from the marrow of bones emerging from the frozen north of Siberia. However, these cells will degenerate rapidly at the temperature of melting snow and ice. This means that cells in the bones may well become useless for this capacity as they thaw.

The chances of cells being viable would be increased if bones could be recovered from the lowest possible temperature rather than waiting until they emerge from snow. The cells can then be warmed rapidly. Alternatively, the nuclei could be transferred directly into eggs.

The very first stages of embryo development are controlled by proteins that are in the egg when it is shed by the ovary. One for example has a critical role in cell division. Together these proteins have an extraordinary ability to repair damaged nuclei so it may not be strictly necessary for the cells to be viable. It would be best if the mammoth nucleus could be introduced into an egg immediately, by injection of the contents of the damaged cell into the egg.

Research in 2008 found that when nuclei from freeze-dried sheep cells were transferred into eggs, some of the cloned embryos developed for a few days, but not to term. This was a very clear indication of the ability of the egg to repair damaged nuclei. However, freeze-dried cells are likely to be more stable than those that have been frozen with liquid still present. In the case of the mammoth, the cells would likely be killed by large ice crystals formed from the liquid.

Finally, if embryos that developed normally for a few days could be produced, they would have to be transferred to surrogate mothers to develop through pregnancy. Embryo transfer is only carried out routinely in fewer than a dozen species, and the elephant is not one of them. Success in embryo transfer depends upon introducing the embryo to a womb that is in a receptive state. The mechanisms that bring about this state in elephants are currently being defined by research in a number of zoos.

Taken together, it can be seen that there is biological uncertainty about the availability of viable cells, and that several complex techniques would have to be developed for cloning of mammoths to be successful. There is no guarantee that these techniques are even biologically possible. There may be unknown differences between species that would prevent the procedures that we developed in sheep being successful in mammoths.

Copyright: Royal BC Museum

Mammoth stem cells
An alternative ambition would be to try to use mammoth cells to produce stem cells. In several different species it is possible simply by the introduction of four selected proteins to give adult cells the characteristics of embryo stem cells. The four factors give embryo stem cells their unique characteristics and were found to be able to impose these characteristics on skin cells. This type of stem cell can be grown for very long periods in the laboratory while retaining the ability to form all of the tissues of the body.

They would provide extraordinary opportunities to compare mammoth cells with those of elephants. This knowledge would be of fundamental biological interest. It would enable us to begin to answer groundbreaking questions. What are the differences between the cells and tissues of these species? What are the similarities? The mammoth lived in a different climate, so was the metabolism of their cells different? Does this information cast any light on the cause of extinction of mammoths?

Stem cells of this type can also be induced to form gametes. If the cells were from a female, this might provide an alternative source of eggs for use in research, and perhaps in breeding, including the cloning of mammoths.

From a male, they would be sperm, and they might be able to fertilise eggs to produce a new mammoth embryo. It would be interesting to know if mammoth sperm could fertilise eggs of the elephant. If so, would the embryos develop to term to produce a hybrid animal?

Only a small proportion of mixed matings between species produces viable offspring, but the mule is one example and has been used by humans for centuries.

In all of these discussions it is necessary to consider the welfare of the animals. Mammoths lived in cold climates, whereas their current relatives including potential surrogate mothers live in warmer regions.

It would be essential to provide mother and clone with the appropriate environment of temperature, moisture and diet. It would almost certainly be necessary to keep the animals in captivity, so it would be essential to provide as interesting an environment as possible. Ideally this should include other elephants, mammoths or hybrids to provide social interaction for the animal.

So while unlikely at present, the development of some form of mammoth creature or hybrid might be possible in the longer term, the research of which could lead to major biological discoveries and advances.

This is another area of biology where studies of stem cells would be very rewarding. In stem cell research rather than cloning there would also be fewer concerns over animal welfare, or the effect of the animal on the environment. All in all, research to produce mammoth stem cells would be the appropriate choice, and extraordinarily scientifically rewarding, should it be possible to find viable mammoth cells.

Sources:

http://theconversation.com/produce-mammoth-stem-cells-says-creator-of-dolly-the-sheep-16335

http://www.theguardian.com/science/2013/jul/31/woolly-mammoth-dna-cloning

Humans have always been the nemesis of the planet’s wildlife

By George Monbiot, published in the Guardian 25th March 2014

A dead elephant in the Hwange National Park, Zimbabwe, thought to have died after poachers poisoned a salt lick with cyanide. Photograph: Aaron Ufumeli/EPA

You want to know who we are? Really? You think you do, but you will regret it. This article, if you have any love for the world, will inject you with a venom – a soul-scraping sadness – without an obvious antidote.

The Anthropocene, now a popular term among scientists, is the epoch in which we live: one dominated by human impacts on the living world. Most date it from the beginning of the industrial revolution. But it might have begun much earlier, with a killing spree that commenced two million years ago. What rose onto its hindlegs on the African savannahs was, from the outset, death: the destroyer of worlds.

Before Homo erectus, perhaps our first recognisably-human ancestor, emerged in Africa, the continent abounded with monsters. There were several species of elephants. There were sabretooths and false sabretooths, giant hyaenas and creatures like those released in The Hunger Games: amphicyonids, or bear dogs, vast predators with an enormous bite.

Professor Blaire van Valkenburgh has developed a means by which we could roughly determine how many of these animals there were(1). When there are few predators and plenty of prey, the predators eat only the best parts of the carcass. When competition is intense, they eat everything, including the bones. The more bones a carnivore eats, the more likely its teeth are to be worn or broken. The breakages in carnivores’ teeth were massively greater in the pre-human era(2).

Not only were there more species of predators, including species much larger than any found on earth today, but they appear to have been much more abundant – and desperate. We evolved in a terrible, wonderful world – that was no match for us.

Homo erectus possessed several traits that appear to have made it invincible: intelligence, cooperation; an ability to switch to almost any food when times were tough; and a throwing arm that allowed it to do something no other species has ever managed – to fight from a distance. (The increasing distance from which we fight is both a benchmark and a determinant of human history). It could have driven giant predators off their prey and harried monstrous herbivores to exhaustion and death.

Artist’s rendition of a prehistoric mastodon. Photograph: Bettmann/Corbis

As the paleontologists Lars Werdelin and Margaret Lewis show, the disappearance of much of the African megafauna appears to have coincided with the switch towards meat eating by human ancestors(3). The great extent and strange pattern of extinction (concentrated among huge, specialist animals at the top of the food chain) is not easy to explain by other means.

At the Oxford megafauna conference last week, I listened as many of the world’s leading scientists in this field mapped out a new understanding of the human impact on the planet(4). Almost everywhere we went, humankind erased a world of wonders, changing the way the biosphere functions. For example, modern humans arrived in Europe and Australia at about the same time – between 40 and 50,000 years ago – with similar consequences. In Europe, where animals had learnt to fear previous versions of the bipedal ape, the extinctions happened slowly. Within some 10 or 15,000 years, the continent had lost its straight-tusked elephants, forest rhinos, hippos, hyaenas and monstrous scimitar cats.

In Australia, where no hominim had set foot before modern humans arrived, the collapse was  almost instant. The rhinoceros-sized wombat(5), the ten-foot kangaroo, the marsupial lion, the monitor lizard larger than a Nile crocodile(6), the giant marsupial tapir, the horned tortoise as big as a car(7) – all went, in ecological terms, overnight.

A few months ago, a well-publicised paper claimed that the great beasts of the Americas – mammoths and mastodons, giant ground sloths, lions and sabretooths, eight-foot beavers(8), a bird with a 26-foot wingspan(9) – could not have been exterminated by humans, because the fossil evidence for their extinction marginally pre-dates the evidence for human arrival(10).

Artist’s rendition of a pack of dire wolves and two mammoths. Photograph: Stocktrek Images/Alamy

I have never seen a paper demolished as elegantly and decisively as this was at last week’s conference. The archaeologist Todd Surovell demonstrated that the mismatch is just what you would expect if humans were responsible(11). Mass destruction is easy to detect in the fossil record: in one layer bones are everywhere, in the next they are nowhere. But people living at low densities with basic technologies leave almost no traces. With the human growth rates and kill rates you’d expect in the first pulse of settlement (about 14,000 years ago), the great beasts would have lasted only 1,000 years. His work suggests that the most reliable indicator of human arrival in the fossil record is a wave of large mammal extinctions.

These species were not just ornaments of the natural world. The new work presented at the conference suggests that they shaped the rest of the ecosystem. In Britain during the last interglacial period, elephants, rhinos and other great beasts maintained a mosaic of habitats: a mixture of closed canopy forest, open forest, glade and sward(12). In Australia, the sudden flush of vegetation that followed the loss of large herbivores caused stacks of leaf litter to build up, which became the rainforests’ pyre: fires (natural or manmade) soon transformed these lush places into dry forest and scrub(13).

In the Amazon and other regions, large herbivores moved nutrients from rich soils to poor ones, radically altering plant growth(14,15). One controversial paper suggests that the eradication of the monsters of the Americas caused such a sharp loss of atmospheric methane (generated in their guts) that it could have triggered the short ice age which began 12,800 years ago, called the Younger Dryas(16).

And still we have not stopped. Poaching has reduced the population of African forest elephants by 65% since 2002(17). The range of the Asian elephant – which once lived from Turkey to the coast of China – has contracted by 97%; the ranges of the Asian rhinos by over 99%(18). Elephants distribute the seeds of hundreds of rainforest tree species; without them these trees are functionally extinct(19,20).

Is this all we are? A diminutive monster that can leave no door closed, no hiding place intact, that is now doing to the great beasts of the sea what we did so long ago to the great beasts of the land? Or can we stop? Can we use our ingenuity, which for two million years has turned so inventively to destruction, to defy our evolutionary history?

http://www.monbiot.com

References:

1. eg Wendy J. Binder and Blaire Van Valkenburgh, 2010. A comparison of tooth wear and breakage in Rancho La Brea sabertooth cats and dire wolves across time. Journal of Vertebrate Paleontology. http://www.tandfonline.com/doi/abs/10.1080/02724630903413016#.UzBUcM40uQk

2. http://www.eci.ox.ac.uk/news/events/2014/megafauna/valkenburgh.pdf

3. Lars Werdelin, 2013. King of Beasts. Scientific American. http://www.scientificamerican.com/magazine/sa/2013/11-01/

4. http://oxfordmegafauna.weebly.com/

5. Diprotodon.

6. Megalania.

7. http://www.wired.com/wiredscience/2010/08/last-giant-land-turtle/

8. Castoroides ohioensis

9. The Argentine roc (Argentavis magnificens).

10. Matthew T. Boulanger and R. Lee Lyman, 2014. Northeastern North American Pleistocene megafauna chronologically overlapped minimally with Paleoindians. Quaternary Science Reviews 85, pp35-46. http://dx.doi.org/10.1016/j.quascirev.2013.11.024

11. http://www.eci.ox.ac.uk/news/events/2014/megafauna/surovell.pdf

12. Christopher J. Sandom et al, 2014. High herbivore density associated with vegetation diversity in interglacial ecosystems. Proceedings of the National Academy of Sciences, vol. 111, no. 11, pp4162–4167. http://www.pnas.org/cgi/doi/10.1073/pnas.1311014111

13. Susan Rule et al, 23rd March 2012. The Aftermath of Megafaunal Extinction: Ecosystem Transformation in Pleistocene Australia. Science Vol. 335, pp 1483-1486. doi: 10.1126/science.1214261. https://www.sciencemag.org/content/335/6075/1483.full

14. Christopher E. Doughty, AdamWolf and Yadvinder Malhi, 11 August 2013. The legacy of the Pleistocene megafauna extinctions on nutrient availability in Amazonia. Nature Geoscience vol. 6, pp761–764. doi: 10.1038/ngeo1895. http://www.nature.com/ngeo/journal/v6/n9/full/ngeo1895.html

15. Adam Wolf, Christopher E. Doughty, Yadvinder Malhi, Lateral Diffusion of Nutrients by Mammalian Herbivores in Terrestrial Ecosystems. PLOS One, doi: 10.1371/journal.pone.0071352. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0071352

16. Felisa A. Smith, 2010. Methane emissions from extinct megafauna. Nature Geoscience 3, 374 – 375. doi:10.1038/ngeo877. http://www.nature.com/ngeo/journal/v3/n6/full/ngeo877.html

17. Fiona Maisels, pers comm. This is an update of the figures published here: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0059469

18. http://www.eci.ox.ac.uk/news/events/2014/megafauna/campos.pdf

19. http://www.eci.ox.ac.uk/news/events/2014/megafauna/campos.pdf

20. http://www.eci.ox.ac.uk/news/events/2014/megafauna/galetti.pdf

Sources: http://www.monbiot.com/2014/03/24/destroyer-of-worlds/

http://www.theguardian.com/commentisfree/2014/mar/24/humans-diminutive-monster-destruction?

Ice-age animals live on in Eurasian mountain range

by Colin Barras

It is the land that time forgot. Not only have conditions in the Altai-Sayan region in central Asia barely changed since the last ice age, but the mix of mammals that lives there is also almost the same.

Věra Pavelková Řičánková and colleagues at the University of South Bohemia in České Budějovice, Czech Republic, compiled lists of mammals living at 14 sites across Eurasia. They compared them with mammals that lived at seven Eurasian sites during the last glacial period 35,000 to 12,000 years ago.

The team discovered that the combination of mammals found together in the Altai and Sayan mountains of western Mongolia and southern Russia – such as horses, reindeer, saiga antelopes and wolverines – is similar to the ancient glacial communities. There are a few obvious differences, however, such as the lack of mammoths.

These animals do not normally live together anymore, says Pavelková Řičánková. She says the Altai-Sayan is one of the last places on Earth to retain an ice age fauna (PLoS One, doi.org/q2n).

“You’ve basically got a really good modern analogue for the Pleistocene communities,” says John Stewart of the University of Bournemouth, UK.

The Altai-Sayan has not been fully explored, so could hold more surprises. In 2010, snails thought to have died out when the ice melted were found alive there (Journal of Biogeography, doi.org/d4vn4n).

The cold, arid climate is key to the animal community, says Pavel Tarasov of the Free University of Berlin, Germany. The last ice age had a similarly dry climate, so Eurasia was surprisingly free from snow. Grasses flourished, helping feed the many herbivores.

However, there is a better model for conditions in northern Eurasia, says Tarasov. Wrangel, a small island in the Arctic Ocean, retains the plant community of that time. And the last mammoths lived on Wrangel, vanishing just 4000 years ago.

The Altai-Sayan may also have been vital for humanity’s success. The mountains are home to Denisova cave, famous for the 2010 discovery of 50,000-year-old fossils of a new kind of human, the Denisovans. Since then, Neanderthal bones, and tools crafted by Homo sapiens have also been found in the cave. This makes it the only place where we know all three hominins lived.

That may be no coincidence, says Pavelková Řičánková. Conditions in the Altai-Sayan are fairly stable, so ancient humans may have taken refuge there and lived off the diverse game species.

“It looks increasingly like the east [of Eurasia] may have been a refugium,” agrees Stewart.

When the ice age ended, the Altai people left the mountains and spread far and wide. Recent genetic evidence suggests that the first Americans can trace their ancestry to the Altai-Sayan (American Journal of Human Genetics, doi.org/fxq8gx).

This article appeared in print under the headline “Mountains where the ice age lives on”

Source: http://www.newscientist.com/article/mg22129533.800-iceage-animals-live-on-in-eurasian-mountain-range.html

Collapse of the Sahara’s megafauna

By Dr. Sarah Durant, Zoological Society of London, Wildlife Conservation Society, and National Geographic’s Big Cats Initiative

There are few landscapes more evocative and beautiful than the sweeping sands and majestic mountains of the Sahara desert. This land used to be widely populated by large animals uniquely adapted to the harsh and unpredictable desert environment. Their ability to roam freely across a vast landscape following sparse rainfall and forage is key to their survival in an unforgiving habitat.

However, over recent times, there has been a catastrophic decline in wildlife in the Sahara. In a new article  that documents the status of large animal species in the region, we show that, out of 14 species historically found in the Sahara, most have been eradicated from 90% or more of their historical range.

Species such as the Addax used to roam widely across the Sahara, but now number only a couple of hundred individuals – the recently established Termit and Tin-Toumma National Nature Reserve in Niger is one of their last strongholds. Photograph by Thomas Rabeil/Sahara Conservation Fund.

Several species have disappeared entirely. The last known photograph of the iconic Scimitar horned oryx was taken in 1982 by John Newby (photo below), and the species was declared extinct in the wild in 1999 (it only survives now in captivity).

This photo, taken by John Newby from the Sahara Conservation Fund in 1982, is thought to be the last of scimitar-hornedoryx in the wild. Photograph by John Newby/Sahara Conservation Fund.

Less information survives on the precise time of disappearance of another three species that have been eradicated from the region: the lion; bubal hartebeest;  and the African wild dog. Critically endangered addax, dama gazelle and Saharan cheetah cling on in tiny fragmented populations, while endangered populations of slender-horned and Cuvier’s gazelles are not faring much better.

You might think that such a catastrophic collapse of an entire megafauna would be making headlines, and that something would be done to stop it, but it has gone ahead largely unnoticed and unreported.

Deserts have become almost invisible on the conservation agenda. World attention has, understandably, focused on the rich biodiversity found in hotspots, which are often in tropical forests. However, deserts actually harbour surprisingly high levels of biodiversity, able to thrive in a harsh and highly variable environment.  This biodiversity hides a wealth of adaptations that enable species to tolerate water stress and extreme temperatures; information that may prove critical as we are forced to adapt to a changing climate.

Unsustainable hunting and past and ongoing insecurity have undoubtedly played a key role in the loss of Saharan wildlife, but it is difficult to avoid the conclusion that more attention might have helped prevent some of the declines. Rare antelope and Saharan cheetah can still be found in remote and inaccessible corners of the Sahara, in vast landscapes possessing a silent peace and unforgettable beauty.

There are also some good news stories—Niger has just established a massive 97,000km2reserve—Termit and Tin Toumma National Nature Reserve, which harbours most of the world’s 200 or so remaining wild addax and one of a handful of surviving populations of dama gazelle and Saharan cheetah. While there is hope that we may yet see scimitar horned oryx back in the wild in the Ouadi Rimé-Ouadi Achim Game Reserve, with the support of the Chadian government.

2014 is the halfway point in the United Nations Decade for Deserts and the Fight against Desertification and the fourth year of the United Nations Decade for Biodiversity. It is an opportune time for the world to focus on securing the sustainable management of desert ecosystems, to the benefit of people and wildlife. The world will be a poorer place if the unique biodiversity of the Sahara and other deserts is allowed to disappear.

Saharan landscapes, such as found in the Ahaggar Cultural Park photographed here, are stunningly beautiful. Photograph by Sarah Durant/Zoological Society of London.

Source: http://newswatch.nationalgeographic.com/2013/12/03/117914/

Access to the scientific paper:

http://onlinelibrary.wiley.com/doi/10.1111/ddi.12157/abstract

More about it:

http://www.scienceworldreport.com/articles/11354/20131204/catastrophic-decline-in-sahara-s-wildlife-population-study-cautions.htm

 

Climate change, not human activity, led to megafauna extinction

Most species of gigantic animals that once roamed Australia had disappeared by the time people arrived, a major review of the available evidence has concluded.

The research challenges the claim that humans were primarily responsible for the demise of the megafauna in a proposed “extinction window” between 40,000 and 50,000 years ago, and points the finger instead at climate change.

An international team led by the University of New South Wales, and including researchers at the University of Queensland, the University of New England, and the University of Washington, carried out the study. It is published in the Proceedings of the National Academy of Sciences.

“The interpretation that humans drove the extinction rests on assumptions that increasingly have been shown to be incorrect.  Humans may have played some role in the loss of those species that were still surviving when people arrived about 45,000 to 50,000 years ago – but this also needs to be demonstrated,” said Associate Professor Stephen Wroe, from UNSW, the lead author of the study.

“There has never been any direct evidence of humans preying on extinct megafauna in Sahul, or even of a tool-kit that was appropriate for big-game hunting,” he said.

About 90 giant animal species once inhabited the continent of Sahul, which included mainland Australia, New Guinea and Tasmania.

“These leviathans included the largest marsupial that ever lived – the rhinoceros-sized Diprotodon – and short-faced kangaroos so big we can’t even be sure they could hop. Preying on them were goannas the size of large saltwater crocodiles with toxic saliva and bizarre but deadly marsupial lions with flick-blades on their thumbs and bolt cutters for teeth,” said Associate Professor Wroe.

The review concludes there is only firm evidence for about 8 to 14 megafauna species still existing when Aboriginal people arrived. About 50 species, for example, are absent from the fossil record of the past 130,000 years.

Recent studies of Antarctic ice cores, ancient lake levels in central Australia, and other environmental indicators also suggest Sahul – which was at times characterised by a vast desert – experienced an increasingly arid and erratic climate during the past 450,000 years.

Arguments that humans were to blame have also focused on the traditional Aboriginal practice of burning the landscape. But recent research suggests that the fire history of the continent was more closely linked to climate than human activity, and increases in burning occurred long before people arrived.

“It is now increasingly clear that the disappearance of the megafauna of Sahul took place over tens, if not hundreds, of millennia under the influence of inexorable, albeit erratic, climatic deterioration,” said Associate Professor Wroe.

Media Contacts: Deborah Smith,  UNSW Science +612 9385 7307, + 61 478 492 060,