A wombat the size of a four-wheel drive. A marsupial lion. A seven metre carnivorous goanna. These creatures may sound like the stuff of nightmares, but in fact all of these once roamed Australia in the not-too-distant past. They are known as the Australian megafauna, and they were widespread during the Pleistocene Epoch (roughly 2,500,000 – 11,000 years ago), a time when Australia, Tasmania and New Guinea were all joined as one landmass due to low ice age sea levels.
The word megafauna comes from the Ancient Greek words for “large” and “animal” and, put simply, that is exactly what they are. The exact classification for what constitutes megafauna is debated but for the most part, if it is bigger than a human, you can be pretty sure you are dealing with megafauna. While modern megafauna, such as elephants and rhinoceros are largely restricted to the African continent (and zoos worldwide), during the Pleistocene Australia had megafauna to rival the best of them.
Among these was the largest marsupial ever discovered, the diprotodontid (genus Diprotodon): a giant relative of the wombat, standing 2 metres tall and weighing up to 2,800 kilograms. Indeed, the Diprotodon would have been such a formidable sight that it has been suggestions that this beast is behind the myth of the bunyip. There was the ferocious Thylacoleo carnifex, a marsupial carnivore the size of a leopard which, pound for pound, had the most powerful bite of any mammal species living or extinct and wielded retractable claws in its semi-opposable thumbs. The structure of the legs of this marsupial suggest it was best adapted to pouncing on prey from treetops, leading some to coin the term “drop cat”.
The largest kangaroo ever discovered, the short-faced Procoptodon goliah, stood two metres tall, weighed in at a hefty 230 kilograms. Many other iconic modern Australian fauna had megafaunal counterparts that were morphologically similar, but much bigger. There was a giant koala (Phascolarctos stirtoni) and an echidna the size of a sheep (Zaglossus hacketti), the largest monotreme ever discovered.
In contrast, one megafauna was quite unlike anything on earth today: the palorchestid (genus Palorchestes), another giant marsupial that reached the size of a horse had with four powerful legs, claws to strip bark from trees and likely a snout-like trunk similar to that of a tapir.
Perhaps most awe-inspiring, however, would have been the Megalania prisca, the giant goanna-like monitor lizard that may have reached lengths of seven metres. Think the komodo dragon is cool? The Megalania prisca could have been up to eight times its size.
The reason why none of these megafauna can be found in Australia today is that they were all wiped out during the devastating Pleistocene mass extinction, with nearly all of the Australian megafauna becoming rapidly extinct approximately 46,000 years ago. What was the reason for this mass extinction of the Australian megafauna? This question has sparked intense debate among the scientific community. The proposed explanations for this mystery fall into two broad categories: the megafauna died out due to extreme climate change during an extremely arid ice age, or the megafauna were hunted to extinction following the arrival of humans in Australia, with many other theories invoking a combination of the two.
Proponents of the hypothesis that climate change alone caused the megafaunal extinction argue that there is no direct evidence for the hunting of the megafauna, such as kill sites or butcher marks on bones. It is also difficult to determine the extent of the contact humans would have actually had with the megafauna, with some researchers arguing that many of the megafauna had died out due to extreme climate variability prior to the arrival of humans.
However the extremely close coincidence of the arrival of humans in Australia suggests that it is likely that humans had something to do with it. Indeed, we do have a history of expediting extinctions, including one of the survivors of the Pleistocene mass extinction: the Thylacine (Tasmanian Tiger). Besides, why would the megafauna choose this time that broadly coincides with human arrival, to suddenly die when they have survived previous cooling trends?
While the dating of these extinctions is made difficult due to the time frame being on the upper limit of the effectiveness carbon radioisotopic dating, researchers have used a range of tools, such as palynology (the geological record of spores and pollen), and optically stimulated luminescence (OSL) to constrain important ages. Some researchers use these methods to counter the argument that the megafauna died out before human arrival and demonstrate that the megafauna died out first and that habitat changed as a result, not the other way around. Additionally, there is strong geological evidence for an increase in wildfires around the time that the megafauna died out, potentially due to human activity, that would have resulted in habitat change and in addition to hunting would have increased duress on the megafauna.
The hypothesis that humans expedited the extinction of the megafauna makes the most sense to me, as it would explain why most of the megafauna worldwide died out around the time when humans first arrived whilst the African megafauna that had coevolved with humans survived, as they would conceivably be less naive and susceptible to hunting. I also have no problem with believing that humans are the root cause of a major blunder: we are pretty good at stuffing things up. That being said, it is likely that the extinction of the megafauna was exacerbated by a number of causes, such as extreme climate, habitat change and increased wildfires, but that it was the additional stress of hunting that finally tipped them over the edge. Whatever the case, unfortunately during the Pleistocene enough factors conspired against the megafauna to wipe them out, leaving us only with the small, furry critters we have today.
Sources & additional reading:
A great index of Australian megafauna:
More on OSL dating:
A good summary of megafauna worldwide:
“Climate killed them” hypothesis:
“Humans killed them” hypothesis:
- Doughty, C. E., Wolf, A., & Malhi, Y. (2013). The legacy of the Pleistocene megafauna extinctions on nutrient availability in Amazonia. Nature Geoscience.
- Koch, P. L., & Barnosky, A. D. (2006). Late Quaternary extinctions: state of the debate. Annual Review of Ecology, Evolution, and Systematics, 215-250.
- McGlone, M. (2012). The hunters did it. science, 335(6075), 1452-1453.
- Price, G. J., Webb, G. E., Zhao, J. X., Feng, Y. X., Murray, A. S., Cooke, B. N., … & Sobbe, I. H. (2011). Dating megafaunal extinction on the Pleistocene Darling Downs, eastern Australia: the promise and pitfalls of dating as a test of extinction hypotheses. Quaternary Science Reviews, 30(7), 899-914.
- Rule, S., Brook, B. W., Haberle, S. G., Turney, C. S., Kershaw, A. P., & Johnson, C. N. (2012). The aftermath of megafaunal extinction: ecosystem transformation in Pleistocene Australia. Science, 335(6075), 1483-1486.