There has been a new development in one of the great battles of Australian science is the question of what killed the megafauna. Last night I heard UNSW Assistant Professor Stephen Wroe on the BBC discussing the latest strike from the climate change side, an indication of just how much this debate has gripped the public imagination.
For those who came in late, Australia was once home to some seriously big beasts. It’s true that wombats the size of rhinos are not quite as impressive as elephants, but the extinct critters have the advantage of being exotic when it comes to our imagination. Moreover, while the ancient herbivores might have had nothing on Africa’s equivalents, the carnivores were something else. Wroe describes the marsupial lion, for example as having “flick blades on its thumbs and bolt cutters for teeth.”* Meanwhile the 5m long goannas of the day probably had two kinds of venom, based on their nearest living relatives.
So why are these fearsome creatures not around any more? There are two main theories – it was the humans what did it, and it was climate change. The human theory comes in several forms. Tim Flannery famously suggested that Aborigines rapidly hunted the beasts to extinction on arrival. However, it is far from clear the early Aborigines had the weapons to bring down some of these fearsome beasts, and there is no undisputed evidence of bones with spear marks for example. Other theories rely on people taking out juvenile megafauna, or on firestick farming changing the landscape to the point where these giant animals could not survive.
Advocates of climate change as the cause point to the lack of evidence of human kills, and have also argued for megafauna surviving along with humans for many thousands of years, making the theory that these beasts didn’t have time to adapt to this new threat less than credible.
The debate has been intense, and from some participants unusually nasty, with much of it centring on contested dating of fossil records.
Now however, Wroe has opened what seems to be a new front in the battle. While it had long been acknowledged that quite a few of the megafauna species disappeared long before humans arrive in Australia, in the Proceedings of the National Academy of Sciences he suggests there were around 90 species that meet the definition of megafauna (presumably using a definition higher than the 44kg limit sometimes applied) in the last million years or so. Of these he says only 8 were definitely around 50,000 years ago when the first humans arrived on the continent, with another 6 as possibilities.
If this is right then obviously humans can’t have been responsible for most of the extinctions. Moreover, if that many species died out then it is hardly a stretch to think that the others would have gone the same way, humans or no humans. Wroe suggests that most of the species were killed off by the extreme arid conditions that prevailed during peak glaciations. Since the last ice age was working its way towards the peak when Aborigines reached here (not surprisingly, as it made the ocean crossings easier) it would make sense for any vulnerable species to drop off at about this point.
Wroe says the paper has had support even from some people who were previously on the anthropogenic side of the debate, but it’s hardly likely to convince everyone – a few years ago Australasian Science carried a feature by someone who claimed their work definitively proved humans were responsible, and basically demanded the other side surrender and admit their mistake.
As I have noted before, this is an example of a real scientific debate, one that should be taught in schools rather than the false battles over evolution or climate science. It’s also something that would be likely to capture students’ imagination. Two tonne wombats taking on 5m poisonous goannas while giant ducks of doom stalk the landscape – all wrapped up in a powerful whodunnit. That is a story worth telling.
*Wroe has made something of a name for himself by measuring the force various living animals can apply with their jaws, and conducting reconstructions that estimate the strength of extinct species. He concluded that the Sabre Tooth Tiger for example, while fearsome in other ways, didn’t have much of a bite, comparing it to a toothless old moggy. If memory serves he concluded that the most powerful bite ever belonged to Megalodon, an extinct relative of the Great White Shark that fed on whales, which would have beaten Tyrannasaurus in a biting contest with ease, should certain spatial and temporal issues not have prevented the encounter. Wroe also found that the marsupial lion’s bite was amongst the most powerful of any known mammal.