Megafauna Extinctions

28 Jan 2017

A tale of two theories - both of them inadequate in their own ways. At ... we have the claim humans wiped out Australian megafauna which just happens to fall hard on the heels of the news that Australian Aborigines  were living in interior Australia between 45,000 and 49,000 years ago (conveniently just prior to the extinction of the megafauna). The paper is in Nature Communications (Jan 20th 2017) but involves some very interesting information about climate as a result of a sediment core off the SW coast (on the continental shelf). This, on the face of it, would seem to reveal it was dry land during a large part of the last 100,000 years. However, the paper actually assumes the core is composed of run-off (from the land into the ocean) and this is not unreasonable if we are talking about catastrophic events. One would have to keep an open mind for the moment as we know the continental shelf was dry land for some parts of the last 100,000 years  - but it is not necessary to think it was entirely emerged. The sediment core included material formed on dry land such as dust, pollen, ashes (presumably from landscape fires) and spores from a fungus that is known to live on dung etc. The core is said to reach back to 150,000 years ago - so a lot of information was produced. For most of that time there is abundant evidence of megafauna but around 45,000 years ago the spores went into a nosedive, we are told, over a period of time lasting several thousand years. The megafauna subsequently collapsed altogether- which brings us up to the otherwise well documented event(s) between 40 and 30,000 years ago. It seems the authors may have raised the bar a trifle by saying the collapse set in at 45,000 years ago - which is where the Aborigines come in. They adhere to the theory that human hunters were responsible for the mass die-off (chasing great big animals around with their spears). The researchers make the point there is no evidence of climate change at 45,000 years ago - but this is at least 5000 years prior to anything of note happening (the two events dated between 40 and 30,000 years ago). The study also calls this 5000 year period 'imperceptible overkill' - which probably means the evidence is so slight that it is not discernible (unless wrung out of the models). 

At ... the opposite theory is addressed, climate change. No other theories are apparently thought feasible, particularly the idea of catastrophe. These two theories vie against each other. One side publishes a paper and the other side responds to counter it. We have two polarised positions - and probably neither are responsible. Once again the really interesting stuff is in the detail (rather than the explanations presented). During the last Ice Age Australia, Tasmania and New Guinea were a single land mass = Sahul. It was inhabited by megafauna - the equivalent of large mammals in the northern hemisphere. By 30,000 years ago 'most' of them had disappeared. The factors involved remain a matter of considerable controversy we are told. Many 'experts' say they were hastened into extinction by hunting. Others by climate change, it adds. The common view is that the interior gradually dried out - and it was not a rapid event. In the second study the teeth and diet of animals living 350,000 years ago were investigated - and compared with animals living between 40 and 30,000 years ago. All in all, they produce evidence that could support some major changes in the environment - but instead of presenting this as evidence of abrupt change they are programmed to solely think in terms of slow change (and therefore stretch the event(s) aka small local change over roughly 10,000 years. No mention is made of decline in human numbers - which would have occurred whatever scenario is adopted. In EuroAsia the period is associated with a well known decline in Neanderthal numbers - and their disappearance. Why isn't this true of Australia? Perhaps the numbers are unknown as it has been assumed Aborigines arrived after 40,000 years ago.