When did Australian Megafauna when extinct?

It has previously been argued that all Australian megafauna went extinct by 46,000 years ago. Because this may be close to the time of human arrival this conclusion has been used to support a model known as 'blitzkrieg', the near instantaneous mass extinction of megafauna through human hunting.
However, Australian fossil megafauna have been found in sites dated at much younger than 46,000 years old. Advocates of a major human role have argued that sediments in these younger sites were disturbed, arguing that previously buried bones could have been introduced into younger sediments. If correct, this would have meant that dates from these younger sites were unreliable.

The best-known site yielding young megafaunal remains is Cuddie Springs, located in south-eastern New South Wales. The research team used a novel chemical forensic test developed by Dr Trueman to test whether bones had been disturbed and moved after death.

Megafauna.....extinct!

Diprotodon
Weighing in at almost 2,700 kilograms, standing two meters tall and having a length of almost three meters, the Diprotodon was nearly 32 times as heavy as the Red Kangaroo; the largest marsupial alive today. It carried its young in a pouch, had wombat-like feet, and relatively long legs. It inhabited forests, woodlands, billabongs, and grassland where it grazed on all variety of vegetation. The giant marsupial Diprotodon was related to the kangaroo, but grew to the size of a present-day rhinoceros. The skull alone was over 1 m (3 ft) in length and was adapted for eating plants. The fossil remains of this giant marsupial are restricted in their distribution to Pleistocene deposits in Australia.
The Diprotodon was probably preyed upon by Marsupial Lions, Humans, and Megalania.

Megalania
Some people believe that the myth of dragons was inspired by the discovery of dinosaur bones. Others believe it was inspired by the Komodo Dragon; a three-meter-long lizard living on the Indonesian island of Komodo. Although the Komodo Dragon is quite large, it doesn't intimidate people anywhere near as much as the Megalania once did.
The Megalania was a lizard roughly the size of a Crocodile. Weighing in at almost approximately 940 kg and growing up to seven meters in length, it was able to tackle three-meter-tall Kangaroos, Wombats the size of cars and perhaps ate the odd human for a bit of variety in its diet. It was an ambush predator that probably waited near water for passing prey.
Like the Komodo Dragon , the Megalania was very efficient in maximising energy from its kills. While some mammalian predators might leave behind 25 - 30 per cent of its prey, the Magalania consumed almost everything, including fur, feathers, and ones. Not only would it have consumed almost everything, very little would have been excreted. Whereas a mammalian predator excretes between 32-37 per cent of what it eats, the Megalania only excreted between 8-13 of what it ate.

Marsupial Lion (Thylacoleo carnifex)
Pound for pound, the Marsupial Lion had the most powerful bite of any mammal that has ever lived. It was capable of inflicting a bite three times more powerful than placental lions twice its size. Estimates about the weight of the Marsupial Lion have varied. It was roughly similar in length and height to a Leopard, but it was more robust. Some estimates have put its weight at between 112 and 143 kilograms, which is similar to an average Tiger. The Marsupial Lions hunting style was probably similar to a leopard. They had strong forearms, and retracting claws that made it possible for them to climb trees. There they would wait for an animal to walk beneath them.

Kangaroos....and a bit on Koalas!!!!

The native animals that survived the ecosystem collapse were those that humans found difficult to hunt. The Kangaroo was one such animal. Although it congregates in groups, unlike a sheep or cow, the Kangaroo is not a herd animal. If a mob of Kangaroos is attacked, individuals run in different directions which makes them difficult to kill on mass. Humans soon adapted by using fire in hunting. With fire, a mob of Kangaroos could be herded towards a group of people waiting with spears. Unfortunately, the use of fire further contributed to the drying of Australia and continued the expansion of the desert. Eventually, eucalyptus forests, which recover quickly from fire damage, were all that remained in Australia. Koalas aside, eucalypts are not suitable for large browsing animals. A bountiful land of rainforests and large animals had become a land of desert, eucalyptus and small animals adept at avoiding humans.

http://www.convictcreations.com/aborigines/megafauna.html

Pleistocene .....

Australia and New Guinea lost around 55 species of mammals towards the end of the Pleistocene. The species that disappeared in this wave of extinction are collectively termed the megafauna because many of them were very large, and the event is refereed to as the late Pleistocene megafauna extinction.

The extinct large mammal herbivores of the late Pleistocene can be divided into two major groups : large wombat-like creatures, as well as true wombats and a giant koala; and wonderfully diverse set of kangaroos, consisting of some larger relatives of living kangaroos and the completely extinct short-faced kangaroos. In all, 10 families were affected by the ‘megafauna’ extinctions and most of them lost a large proportion, if not all, of their species.

OVERKILL

Hunting megafauna as a specialised activity which provided a large proportion of food for early human population and hunting as a relatively minor component of a broad hunter-gatherer economy. In the first case, the rate of growth of the human population would have depended strongly on the availability of megafauna prey. But the evidence for human hunting of extinct megafauna is slight and, at best, ambiguous. There are no unmistakable ‘kill sites’ with evidence of the systematic slaughter and use of many individuals of the extinct species. Worse still, there is no evidence that Aboriginal people had weapons typically associated with big-mammal hunting during the period that megafauna disappeared. Beforehand it seems that people used only simple wooden implements for hunting. These might have been effective in killing the occasional giant marsupial but seem inadequate to the task of wiping 50 species from a continent.

In the interval leading up to the coldest and driest phase of the last glacial cycle environment pressures on large mammal presumably increased as Australia became more arid. Many people have suggested that this changed at least contributed to the late Pleistocene extinctions (Arch 1984; Field & Dodson 1999; Horton 1984; Kohen 1995). The effects on megafauna of the deterioration ice age climate have been conceived in two major ways. First, the major impact could have come from an increase in climate variability, as might well have accompanied the transition from one climate regime to another. Main (1978) suggested that an unstable climate would have been to the disadvantage of large-bodied species because of their generally low rates of population growth. A population of a small-bodied species knocked down by an extreme climate event, like a severe drought, might be able to recover while the next one hit; populations of large-bodied species, unable to rebound quickly, could be driven down to very small numbers and ultimately to extinction by a series of extreme events.

Second, a general reduction in the rainfall would have reduced the avail-ability of drinking water and the productivity and nutritional quality of vegetations. Large mammals are the most vulnerable to those changes because of their large-requirements for food and water.

Merrilees(1968) and Jones (1968) argued the landscape burning by Aboriginal people brought about major changes to Australian vegetation, which if not the sole cause were a very significant part of the complex of factors that drove the megafuana extinct. Surely, the argument went, this level of use of fire must have changed the vegetation dramatically over practically the whole of the continent, and it may have destroyed the habitat of many megafauna species. Many of the extinct megafauna seem to have been animals of open grasslands, woodlands and shrub lands. When Europeans first came to Australia they found vast areas of such habitats under Aboriginal burning. If there is no reason to think that species like Diprotodon optatum and procoptodon goliah needed radically different habitats to those that existed over most of the continent two hundred years ago, it is hard to imagine how a changed in habitat cause by Aboriginal burning could have wiped them out. In many cases the most sensible view might be that burning favoured them, as it does some of the largest herbivores in Australia today. As Horton(2000) said ‘If creating grasslands in Australia was good for cows and sheep [it] would have been just as good for the Diprotodons.”

A more subtle version of the hypothesis is as follows. Before the arrival of people many habitats of inland Australia had a complex layer of shrubs and small trees, which was important to the large number of megafauna species that were browsers. An increase in burning removes or simplified this vegetation layer over large areas. Nonetheless, landscape burning continues to be invoked in general terms as a factor that might have contributed to at least some of the extinction.

Past and Present

The loss of oolacunta (rat-kangaroo) was just one of the latest in a long series of extinction that have depleted Australia’s mammal diversity in the geologically recent past. One hundred thousand years ago there were at least 340 species of land mammals in Australia; 67 of them are now extinct. These extinctions came in three waves. First, some time in the last glacial cycle( the late Pleistocene, between 130000 and 10000 years ago), over 50 species of mainly very large marsupials disappeared. Next, in the Holocene (between 10 000 and 200 years ago), the remaining large carnivores declined to extinction on the mainland. Finally, in the two hundred years or so since European settlement a further ten marsupial species is now threatened with extinction.

Are there other reason for the loss of the megafauna...

The main reasons as to how we lost the megafauna are as follows:

Human Impact: We needed a lot of land to support our lifestyles over the years, so many forest got deforest. None of the forest revived so native animals and plants that live there lost their habitat. The others are hunting or excessive burning off in the grass lands.
One of the biggest causes of the extinction of megafauna was because of when the humans arrived around 48,000-60,000 years ago.

Aboroginal burning: They burnt the land for a whole range of reasons. They burnt the land so that they can move across it easily. They hunt along the fire front. They signal distant bands. Fire promotes the growth of beneficial plants that sprout after burning. So there are many reasons why humans might be burning the landscape in a way that they thought would have a positive impact. The Australian landscape is unique in that it has extremely low nutrients in the soils, because it's a very ancient, flat landscape, and most of the nutrients have already been removed from the soil. So it has a high sensitivity to burning having a big impact. Large animals in the interior of the continent were eating just such a mixture—feasting on nutritious grasses in years with good rains, and depending on trees and shrubs in drier years. After 45,000 years ago, those nutritious grasses were nearly gone, and those animals that hadn't gone extinct were restricted to dominantly tree and shrub dietary sources.

Natural Disasters: There are theories that natural disasters like a severe drought or blizzard killed the megafauna. A volcanic eruption is one of the theories too.

Mass Diseases: Diseases, infections or viruses could have swept Australia killing all the megafauna.

Change in Temperature: There could have been a big shift in temperature making it too hot or too cold for the megafauna to survive.

Invasion by non-native plants/animals. Other plants/animals are brought to Australia for certain reasons. Species that are already living there wouldn’t get used to the them. This can cause more problems.

how the climate change over time in Australia......

When Australia broke off from Antarctica maybe 50 or 60 million years ago, it was at a high southern latitude, where conditions were usually moist and cool. It had forest over the whole country, so it had a very damp, cool and forested land. Then it slowly drifted north towards Asia, and in that process, it moved from those temperate latitudes to the subtropical high-pressure zone, where the continent became both warmer and drier. Therefore, the inner of the continent in particular dried out. And the fossil record shows the vegetation and the fauna adapting to those much more dry conditions.

Superimposed on the long-term shift from that a cool, moist climate into subtropical aridity, the world entered an ice age about two million years ago with glacial/interglacial cycles. Consequently, the last two million years of that 50 million-year journey was a period of high-amplitude climate change, from relatively warm, wet climates to much drier and colder climates, back and forth repeatedly. And these transitions occurred rapidly, many times over a few hundred to a few thousand years. This would have been a very different kind of climate stressor from the more gradual shift towards aridity.

Credit: http://www.pbs.org/wgbh/nova/bonediggers/extinction.html

Could the plants have played a role in the extinction of megafauna?

If the plants that the animal eats go extinct, then the animal would have no food to eat, and eventually they will die out. Therefore, the food chain is disrupted and this could be cause of the extinction of megafauna. The same effect goes for today, if vegetation dies out, the same scene will appear again.

Did climate change affect the extinction rate of the megafauna?

Did climate change affect the extinction rate of the megafauna?

Maybe, maybe not. We have no certain data to prove or disprove this theory, it is to early for us to know. Most of the people we interviewed said that climate change could have been a reason for the extinction rate of megafauna. Also we must remember that these animals had survived 2 million years on earth, and would have endured any previous climate change that occurred.

There's no clear evidence that the ice-age cycles themselves led to any of the big extinctions.

Tribute To Extinct Australian Megafauna

What is Megafauna?

Have you ever seen a giant wombat in Australia? Of course not because they don't exist anymore. But once upon a time they did, along with other giant animals.

Megafauna literally means BIG animal.
Mega + Fauna = Big + Animals. Any mammal weighing more than 100 pounds (45 kilograms) are considered as megafauna. Excluding dinosaurs however because they're in a category of their own. Long after the extinction of dinosaurs, megafauna roamed Australia. Giant flightless birds, hippo-sized diprotodonts and the world's largest ever land-dwelling lizards make up the megafauna, which went extinct around 30-50,000 years ago.