A perfect storm involving a rapidly warming climate and the arrival of predatory humans finally led to the extinction of the South American horse and other large land mammals in the south of the continent, research has shown.
Giant Ice Age species once roamed the windswept plains of Patagonia, in southern South America, but scientists have been unable to unravel the circumstances that led to the sudden die-off of these species.
Now, research led by the Australian Centre for Ancient DNA at the University of Adelaide, published this week in the journal Science Advances, has revealed that it was only when the climate warmed, long after humans first arrived in Patagonia, that the megafauna finally succumbed.
The timing and cause of rapid extinctions of the megafauna has remained a mystery for centuries.
“Patagonia turns out to be the Rosetta Stone – it shows that human colonisation didn’t immediately result in extinctions, but only as long as it stayed cold,” said study leader Professor Alan Cooper, who heads the Ancient DNA centre.
“Instead, more than 1000 years of human occupation passed before a rapid warming event occurred, and then the megafauna were extinct within a hundred years.”
That occurred around 12,300 years ago.
The researchers, including from the University of Colorado Boulder, University of New South Wales and University of Magallanes in Patagonia, studied ancient DNA extracted from radiocarbon-dated bones and teeth found in caves across Patagonia, and Tierra del Fuego, to trace the genetic history of the populations.
Species such as the South American horse, giant jaguar and sabre-toothed cat, and the enormous one-tonne short-faced bear – the largest land-based mammalian carnivore – were found widely across Patagonia, but seemed to disappear shortly after humans arrived.
The pattern of rapid human colonisation through the Americas, coinciding with contrasting temperature trends in each continent, allowed the researchers to disentangle the relative impact of human arrival and climate change.
“The America’s are unique in that humans moved through two continents, from Alaska to Patagonia, in just 1500 years,” said Professor Chris Turney, from the University of New South Wales.
“As they did so, they passed through distinctly different climate states – warm in the north, and cold in the south. As a result, we can contrast human impacts under the different climatic conditions.”
The only large species to survive were the ancestors of today’s llama and alpaca – the guanaco and vicuna — and even these species almost went extinct.
Lead author Dr Jessica Metcalf, from the University of Colorado Boulder, said: “The ancient genetic data show that only the late arrival in Patagonia of a population of guanacos from the north saved the species. All other populations became extinct.”
Dr Fabiana Martin, from the University of Magallanes, said Fell’s cave, a small rock shelter in Patagonia, was the first site in the world to show that humans had hunted Ice Age megafauna. Crucial discoveries were made there in 1936.
“So it seems appropriate that we’re now using the bones from the area to reveal the key role of climate warming, and humans, in the megafaunal extinctions,” he said.
The researchers acknowledged that the causes of Late Pleistocene megafaunal extinctions, from 60,000 to 11,650 years ago were contentious, with major phases coinciding with both human arrival and climate change around the world.
They said the Americas provided a unique opportunity to disentangle these factors as human colonization took place over a narrow time frame, around 15,000 to 14,600 years ago, but during contrasting temperature trends across each continent.
The study team conducted genetic analysis on 89 Patagonian megafaunal bones and radiocarbon-dated 71 of them for the study. Their work more than doubled the high-quality Pleistocene megafaunal radiocarbon data sets from the region.
Their work identified a narrow megafaunal extinction phase 12,280 years ago, plus or minus 110 years, some 1000 to 3000 years after the arrival of humans in the area.
Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation
Jessica L. Metcalf, Chris Turney, Ross Barnett, Fabiana Martin, Sarah C. Bray, Julia T. Vilstrup, Ludovic Orlando, Rodolfo Salas-Gismondi, Daniel Loponte, Matías Medina, Mariana De Nigris, Teresa Civalero, Pablo Marcelo Fernández, Alejandra Gasco, Victor Duran, Kevin L. Seymour, Clara Otaola, Adolfo Gil, Rafael Paunero, Francisco J. Prevosti, Corey J. A. Bradshaw, Jane C. Wheeler, Luis Borrero, Jeremy J. Austin and Alan Cooper.
Science Advances 17 Jun 2016: Vol. 2, no. 6, e1501682