Rapid Warming and Humans Drove the Ice Age Extinction of Patagonia's Megafauna

At the end of the last ice age (11,000 to 18,000 years ago), the world suddenly lost some of the most remarkable creatures that ever roamed our planet. Patagonia in southern South America was particularly rich in creatures that could only be labelled bizarre today: elephant-sized sloths, giant jaguar, powerful sabre-toothed cats and an enormous one-tonne short-faced bear (the largest ever land-based mammalian carnivore). What caused their demise is  one of the big geological whodunnits. 

Last year you may remember we had a research paper published in Science that looked at megafaunal extinction in North America and Eurasia. Whilst warming looked like it was a driver of the extinctions in the Northern Hemisphere, there was a tantalising hint that humans had also played a role. But disentangling the effects of both was challenging.  To test their roles we have extended our work to Patagonia and the results are now published in the The American Association for the Advancement of Science journal  Science Advances. The article is called Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation and can be downloaded for free. 

The Americas are the only place in the world where we have a north-south transact along which humans migrated very quickly. The important difference is at the extreme ends of both continents during the end of the last ice age, the climate was wildly different. As the planet warmed up, the climate veered violently from one extreme to the other, often at different times and places. When it was warm in the north, it was often cold in the south, and vice versa (something loosely described as the 'bipolar seesaw').

Photo of an ancient guanaco jaw excavated from Cueva del Mylodon (or Mylodon Cave), Patagonia, which was used for ancient DNA analysis. Photo by Alan Cooper/Malmö Museum.

In this study headed up and led by Australian Centre for Ancient DNA (ACAD) Alan Cooper and Jessica Metcalf (with an awesome international team), we've undertaken the most intensive carbon dating and DNA analysis of ancient Patagonian bones yet undertaken. The results are a revelation. We've been able to identify new species that became extinct and confidently line them all up against the archaeological evidence and climate records. As a result we can finally disentangle the role of humans and climate in extinction. The headline is both seem to play a role...together. When climate first warmed at the end of the last ice age in Patagonia the megafauna suffered no extinction. Humans arrived during a later 2000-year long period of cooling known as the Antarctic Cold Reversal (or ACR for short) and there was still no extinction. But when the ACR ended and warming resumed, the mix of climate and humans was a perfect storm that led to widespread mass extinction. We're really excited. It finally feels we're getting a handle on what actually happened thousand of years ago and in the process hopefully a step closer to better managing the impact of current and future warming.

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