Mungo Man
A 60,000-year-old mystery

Bradshaws
The first civilisation?

Cities
Why didn't Aborigines build cities?

Dreamtime
A time of creation

Migrant Flora and Fauna
Long history of migration

Megafauna Extinction
Hunting or climate change

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The Extinction of Australian Megafauna

Today, wide-scale burning of the Amazon runs the risk of turning rainforest into savannah. In a rainforest, 50 per cent of rainfall gets recycled by the ecosystem. Rain falls, is trapped, sucked up by trees, released into the atmosphere, reaches a critical humidity and then falls again at a different location. When the land is cleared; however, not only does less recycling occur, less rain falls. The ecosystem then collapses forever.

50,000 years ago in Australia, large-scale burning of the land likewise turned rainforest into savannah, and then into desert. After the foliage was razed to the ground, rain fell and soaked into the sand or quickly evaporated under the scorching sun. In turn, a reduction in humdity decreased the number of clouds forming.

In 2004 and 2005, Dr John Magee and Dr Michael Gagana from the Australian National University showed that burning caused a decrease in the exchange of water vapour between the biosphere and atmosphere. Clouds stopped forming and the annual monsoon over central Australia failed. Whereas once the Nullarbor Plain was home to forests and tree dwelling Kangaroos, now it is desert. Likewise, Lake Eyre, formerly a deep-water lake in Australia's interior, is now a huge salt flat occasionally covered by ephemeral floods. (1)

The revelations of human induced climate change married the previous two competing theories regarding the extinction of the megafauna. Previously, one group of scientists had argued that natural climate change caused the extinctions. This approach failed to explain why the megafauna had survived more extreme climatic changes over the last 1.5 million years. Another group of scientists had argued that humans had hunted megafauna to extinction. This approach failed to explain why the fossil record showed evidence of ecosystem collapse associated with climatic change.

As human induced climate change caused the rains to fail, it was impossible for humans to remain in balance with the ecosystem. When Australia had been fertile, their population densities had been high and may have been in balance with megafauna. When the ecosystem collapsed, they used their skills of adaptation to hunt megafauna to extinction.

The native animals that survived the ecosystem's 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.

Megafauna and humans co-existing

Cuddle Springs in north central NSW is currently the only place in Australia where evidence has been found of megafauna and humans co-existing. Excavations by a team from the University of Sydney has found evidence that megafauna were living at the site 30,000 years ago. If correct, this means that they must have survived the human-induced climate change and also lived alongside humans for a further 15,000 years.

As the megafauna bones contain undetectable amounts of protein, no direct dating methods have been used. Consequently, some scientists have argued that the process of site formation may have involved some mixing of materials of different ages. This mixing may have created a perception of co-existence where none actually occured.

If one takes a view that the University of Sydney's estimates are accurate, there is a small chance that the megafauna was farmed by humans. The now extinct Diprotodon may have been suitable for animal husbandry. Weighing 32 times as much as a Red Kangaroo, it could have been enclosed in a pen and humans could have fed on its blood, milk and flesh. The Genyornis was another. A flightless bird four times larger than an Emu, it could have been enclosed in a pens and humans could have fed on its eggs and flesh.

If humans were farming the Megafauna, they could have preserved them at Cuddle Springs long after they had been hunted to extinction around the rest of Australia. An unusual feature of the dig at Cuddle Springs is that the Diprotodon is one of the few animals that was associated with human butchering tools. If the humans were merely hunter gatherers, many of the smaller animals should also also have lived alongside them and also been associated with butchering tools.

Grinding stones are the only direct evidence of farming at Cuddle Springs. Grinding stones are typically found in agricultural societies. The presence of 30,000-year-old grinding stones at Cuddle Springs is quite unusual because they predate all other grinding stones around the world by 20,000 years.

*At present, no researchers argue that the humans that existed at Cuddle Springs were anything other than hunter gatherers.  

Climate change was the cause of Megafauna extinction

In 1998 David Bowman, an ecology expert from Charles Darwin University, argued that humans did not have the population density or the technology to efficiently wipe out megafauna.  According to Bowman:

"It should be remembered that it becomes increasingly difficult to kill off a species as their population is reduced to low levels because of the extra hunting effort required to find the last remaining animals." (2)

While Bowman was correct in his assertion that a decline in prey numbers would necessitate more work on behalf of the hunters, common sense would also stipulate that as numbers decline, a species' genetic diversity declines with it.  Whether the last animal dies as a result of a spear or disease is irrelevant because it was over hunting the caused population decline. By Bowman's logic, colonists should not have been able to kill off Tasmanian Tigers because as there numbers got low, hunting them would have been too much effort.

As an alternative to the over-hunting theory, Bowman proposed that the megafauna were wiped out by climactic changes. In Bowman's opinion, these climate changes had nothing to do with human action. To the contrary, human action limited the severity of climate change. According to Bowman:

"They intervened and they changed the habitat balance with their fire management practices and, in doing so conserved some habitats, such as rainforest, that might otherwise have been lost during the extreme aridity that characterised the end of the last ice-age some 10,000 to 20,000 years ago." (2)

Like his theory that a decline in population would somehow save a species, Bowman's theory that burning forests somehow preserved them was also shallow in logic. By Bowman's logic, people today should counter the threat of global-warming-induced drought by investing in some flame throwers.

A final problem with Bowman's theory is that almost all the biggest animals appear to have gone extinct well before the ice age reached its maximum, and at least 20,000 years before the megafauna from nth America went extinct. If the climate change was a global phenomenon, megafauna extinction around the world should have happened at a similar time.

University of Queensland PhD researcher Gilbert Price is another who supports the climate change theory of megafauna extinction. Price studied a 10-metre-deep section of creek bed in the Darling Downs region in Queensland's southeast. He found evidence of a very severe drought around 40-50,000 years ago, and megafauna dying, but no evidence of humans. According to Price,

"The research found no evidence of humans being involved in the accumulation of fossils in the catchment at the time of deposition, but is perfectly consistent with their decline being caused by increasing aridity...So it's most likely that Australia's giant kangaroos and other megafauna in this area were driven to extinction by the hands of Mother Nature." (4)

Price's research was useful in that it showed that there was very severe climate changed 40-50,000 years ago in the Darling Down's region. It was not very useful in explaining megafauna extinction. Fossils only form when buried and cut off from oxygen and water. Generally, when humans kill an animal, they do not bury the remains so few fossils form. Consequently, it would not be expected to find evidence of humans killing megafauna unless the region has some kind of mud slides that buried bodies or caves to take the bones to.

Even if humans were not killing megafauna in Darling Downs, just because an animal is dying in a drought in one part of a country doesn't mean humans aren't hunting them in another. I.e, just because Kangaroos die in a drought in Victoria doesn't mean people aren't shooting them in Western Australia, or hunting them in areas where they could have potentially survived a drought. Price was trying to make his research appear more significant than it was. All that his research indicated was that there was climatic change in the Darling Downs region 40-50,000 years ago.

Hunting was the cause of megafauna extinction

Flinders University palaeontologist Gavin Prideaux has argued that the megafauna were hunted by humans. According to Prideaux:

"Our evidence show that the Naracoorte giants perished under climatic conditions similar to those under which they previously thrived, which strongly implicates humans in their extinction...the real issue now is trying to resolve whether it was hunting or whether it was landscape destruction through burning ... and a bit of both is more likely." (3)

Prideaux's view doesn't seem to incorporate research from the ANU showing human-induced climate change. Furthermore, it doesn't seem to incorporate some research showing a relationship between climate change and megafauna extinction. According to the ANU's Dr John Magee and Dr Michael Gagan:

"Neither over-hunting nor human-induced diseases, the two most widely cited alternative agents for a human-caused extinction event in Australia, would result in the dramatic changes at the base of the food web documented by our datasets,...the reduction of plant diversity, however it came about, would have led to the extinction of specialized herbivores and indirectly to the extinction of their non-human predators." (1)

Activity 1 - Make an argument

Activity purpose - Develop skills in research, evaluation, analysis and application

Research the following theories of megafauna extinction and make a list of the evidence in support and the evidence against

1. The megafuna were hunted to extinction by humans
2. The megafauna were wiped out by natural climate change
3. The megafauna were wiped out by environmental changes caused by humans burning the bush
4. The megafauna were wiped out by an introduced disease
5. The megafauna were wiped out by a combination of factors

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 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.

Tribute to extinct megafauna

(Megalania) 

(Megafauna - animated)  

 
(Diprotodon)

1)Burning caused megafauna extinction (http://info.anu.edu.au/ovc/Media/Media_Releases/_2005/_July/_080705magee.asp)

2) Taming the Fire - http://www.abc.net.au/science/future/theses/theses1.htm

3)Giant kangaroo likely killed off by humans - http://www.msnbc.msn.com/id/16359687/

4)Lessons Learned From Drought Deaths 40,000 Years Ago
 http://www.sciencedaily.com/releases/2006/11/061128093019.htm