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MEGAFAUNAL EXTINCTIONS | Entering the Dreamtime:

The Ancient Giants of Ice Age Australia

A model of the rhino-sized Diprotodon optatum, the largest marsupial to ever live

Last month we took a general look at the issue of the megafaunal extinctions that took place across most of the world late in the Ice Age, so this month we will start to focus our attention on the various continents independently, beginning with the one which is thought to have been one of the earliest affected – Australia. Today, this great southern landmass is celebrated for the unique nature of its mammals, it being the only continent on Earth to be dominated by marsupials, but in the late Ice Age it was home to a mammalian fauna of even more wondrous character.

Around 50,000 years ago, due to lower sea levels, Australia was joined to New Guinea and neighbouring islands in a vast landmass called Sahul, and there were a number of gigantic marsupials stalking the ancient lands of this mighty continent, while even the monotremes, birds, and reptiles playing a supporting role were much larger than their counterparts in Australia today. However, not long after this, these ancient giants disappeared from this vast continent for good. As with the other megafaunal extinctions, some of the evidence suggests humans may be to blame, the first ancestors of today’s Aboriginal people having arrived on the continent tens of thousands of years before the Irish first set foot in Australia.

During the Ice Age, Australia and New Guinea were joined together as a gigantic landmass called Sahul

Before we can look at the evidence for human involvement, though, we must first look at the extinction itself and some of the most interesting creatures involved to develop an understanding of just how profoundly Australia's fauna was altered during the late Ice Age.

Indeed, Australia seems to have been one of the continents most heavily affected by the megafaunal extinctions, with one estimate suggesting that as many as 90 per cent of its ancient megafaunal species (those over 45 kilograms) went extinct. This is an incredible figure, and it highlights just what a wealth of animal diversity has been lost from Australia in relatively recent (at least geologically-speaking) times.

One notable aspect of the Australian megafauna is that its members were a bit smaller than those from other continents. For instance, it had no mammal the size of a mammoth or a mastodon, and it has been suggested that this may have been related to the lesser availability of nutrients and habitable land area due to the wide expanse of arid land in the continent’s interior. However, there were still many mammals present which were far larger than the marsupials populating Australia today.

For example, Zygomaturus trilobus, which looked a little like a cross between a rhino and a bear, could weigh up to around half a tonne, while the ‘marsupial tapir’, Palorchestes azeal, which sported long claws and a fairly long trunk, was an even more massive form, capable of reaching over a tonne in weight. However, the undisputed master of Australia’s megafauna, and simply the largest marsupial to ever live, was Diprotodon optatum, which looked somewhat like a rhino-sized wombat and was, by one estimate, an astonishing 2.7 tonnes in weight and around two-and-a-half metres tall at the shoulder.

A young Diprotodon optatum being attacked by the 'marsupial lion' Thylacoleo carnifex

Living alongside these spectacular giants there were other massive marsupials, one of the most impressive of which was the giant short-faced kangaroo, Procoptodon goliah, which was far larger than any kangaroo living in Australia today. This towering kangaroo is thought to have stood at a height of around 2.7 metres, or almost nine feet tall, and may have weighed almost a quarter of a tonne – making it around three times heavier than today’s red kangaroo. Procoptodon also differed from its living relatives in one striking aspect: how it moved. Because of its much greater size, it is thought that this giant kangaroo did not hop across the landscape as modern kangaroos do, but walked.

Of course, the mammalian megafauna of Australia also included some great predators, such as the ‘marsupial lion’, Thylacoleo, which was very cat-like in ways and weighed over 100 kilograms. Other large marsupials were of a somewhat lesser dimension but were, nevertheless, still giants compared to their modern relatives, not least the giant wombat, Phascolonus gigas, while the monotremes – represented today by the platypus and echidna – could also claim some titans, such as the giant echidna, Zaglossus hacketti.

Artist's reconstruction of the 'marsupial lion' Thylacoleo carnifex

Other large non-mammalian megafauna also seem to have gone extinct in Australia during the late Pleistocene, including the giant goose Genyornis newtoni, which, unlike the geese in modern Ireland, was unable to fly. Massive reptiles included a monitor lizard, or goanna, Varanus priscus, which was a close relative of today’s komodo dragon (Varanus komodoensis), although much, much bigger. At nearly three quarters of a tonne (700 kilograms), Varanus priscus was about ten times the weight of its formidable modern relative which stalks the islands of southeastern Indonesia, and it likely preyed on even the largest of the marsupial giants.

Other large reptiles which may have gone extinct at this time include the giant, five-metre-long snake, Wonambi naracoortensis, and the impressive, five-to-six-metre-long terrestrial crocodile Quinkana fortirostrum, which, like Procoptodon, moved about in quite a different way on land than its modern relatives do. While the modern crocodiles of Australia push themselves about on land on their bellies using stubby legs, Quinkana walked about in a far more dignified and lofty fashion, using long legs which kept its body well suspended from the ground.

Late Ice Age Australia, then, was a land of marvels, but this age of giants was not to last and many experts have traditionally thought that most, if not all, of Australia’s megafauna had disappeared by about 46,000 years ago. Supporters of the overkill hypothesis see a clear link between this disappearance and the arrival of humans on the continent, which until recently was thought to have occurred around 50,000 years ago, with the megafauna being driven to extinction by a combination of human hunting and extensive modification of the landscape, for example, through the burning of vegetation.

However, others argue that the evidence for a megafaunal extinction soon after humans arrived in Australia is not very secure and that the extinctions of megafaunal species actually occurred over a much longer period of time and were the result of the continent becoming progressively more arid.

Indeed, different views seem to provide evidence for an acquittal of the Aboriginal peoples' ancestors in different ways. For instance, some experts have claimed that many of the megafaunal species had gone extinct before humans ever settled Australia, while claims have also been made that megafaunal remains found in association with stone tools at some sites, such as Cuddie Springs in New South Wales, date to less than 40,000 years ago, and so provide evidence of a long co-existence of humans and the megafauna.

Locations of important sites mentioned in the text

However, others note that these late dates are largely based on dating of sediments and charcoal, and recent dating of the megafaunal remains themselves has shown them to be over 45,000 or 50,000 years old. Thus, these claims for a long-lasting co-existence of humans and megafauna is heavily disputed.

Over recent years, though, some of the theories regarding human involvement in the demise of the Australian megafauna have come under greater scrutiny. For example, the idea that extensive modification of the landscape by humans through the use of fire, resulting in destruction of the megafauna’s habitats, doesn’t seem to be borne out by the DNA evidence from plants, which do not show any evidence of having experienced genetic bottlenecks from widespread fire use. Also, genetic evidence from the Aboriginal people themselves indicates that their populations may have remained relatively small for tens of thousands of years after their arrival in Australia, only becoming larger around 10,000 years ago. On top of this, a study from early 2017 has provided evidence of human co-existence with megafaunal mammals in one area lasting many thousands of years.

Humans are known to have continuously inhabited the Willandra Lakes region of New South Wales since they first arrived around 50,000 years ago, but in January 2017 a study announced evidence that one of the megafauna, the aforementioned 'rhino-bear' Zygomaturus trilobus, was present in the area at least as late as 33,000 years ago, and possibly much later. What ultimately heralded the demise of this large beast is unknown, but it is possible that the deteriorating climate at this time, as the world descended towards the Last Glacial Maximum (c. 26,000–19,000 years ago), may have brought this megafaunal mammal and humans into closer contact as both were drawn to the lakes due to surrounding areas becoming less water-rich.

However, even if humans played a part in the extinction of this great mammal, the evidence for a long period of co-existence leading up to this indicates that the overkill hypothesis, which envisages the megafauna going extinct soon after the arrival of humans, is not borne out in this case at least.

On top of this, a study published in July 2017 has provided a wealth of new evidence that has pushed back the date for the earliest colonisation of Australia by modern humans by as much as 18,000 years, and possibly more. Up to this point, dates for the arrival of humans in Australia ranged from around 47,000 years ago to around 60,000 years ago, with many settling on 50,000 years ago as a reasonable estimate. However, this new study dating stone tools from a rock shelter near Kakadu National Park in the Northern Territory, to the southeast of Darwin, has found them to be at least 65,000 years old, and possibly older.

This provides further support for the view that the early ancestors of the Aboriginal people may have co-existed with the continent's megafauna for thousands, if not tens of thousands, of years before they went extinct. Indeed, evidence announced in March 2019 from archaeological research in the Warrnambool region of the southern state of Victoria has even revived claims that modern humans had arrived in Australia by around 120,000 years ago, so their co-existence with the continent's megafauna may have lasted many more millennia than even the evidence from near Kakadu National Park suggests.

Ultimately, though, as noted in Dr Anthony Stuart’s 2015 review of the megafaunal extinctions, it is impossible to come to any definitive conclusions as regards the causes of the great megafaunal die-off in Australia, not least because a certain chronology of the extinctions cannot at present be constructed due to most of them occurring either near to or outside the range of radiocarbon dating, which is only effective up to around 50,000 years ago. Yet, this may change in the future as other dating techniques become more effective.

So, whether or not the ancestors of the Aboriginal people had a hand in the destruction of Australia’s megafauna we cannot definitively say, although the latest evidence at least seems to lend less support to a scenario where these great beasts suffered extinction swiftly after humans arrived on the continent. Indeed, to some degree, quite the opposite might be true, and these ancient ancestors of Australia's indigenous people may even have found a way to keep the megafauna alive.

The rich mythology of the Aboriginal people is populated with a variety of massive and outlandish beasts unlike anything found in Australia today, and it has been suggested that the inspiration for these mythological creatures came from the gigantic animals their ancient ancestors encountered when they first made Australia their home. In this way, then, the fascinating creatures of Australia’s late Ice Age megafauna may still live in Australia today, inhabiting the wild realms of the Aboriginal Dreamtime.

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