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Some of the beasts living in Patagonia 13,000 years ago were an intimidating bunch: Fierce saber-toothed cats, elephant-sized sloths, ancient jaguars as big as today’s tigers and short-faced bears that stood 12 feet tall and weighed nearly a ton.

But by 12,000 years ago, they had disappeared. What happened?

A study led by the University of Adelaide and including CU-Boulder shows giant ice age-era mammals that roamed Patagonia were finally felled by a rapidly warming climate, not by a sudden onslaught of the first human hunters.

Led by the University of Adelaide’s Australian Centre for Ancient DNA (ACAD), the study revealed that it was only after the climate warmed, long after humans first arrived in Patagonia, that the large animals known collectively as megafauna suddenly died off.

The timing and cause of the rapid extinction of the megafauna in Patagonia – a geographic region at the base of South America that includes the lower sections of Argentina and Chile – has been a mystery for decades.

University of Adelaide Professor Alan Cooper, study leader and ACAD director, said cold temperatures in Patagonia were present for more than the first 1,000 years of early human occupation there. After the region went through a rapid warming event around 12,500 years ago, the megafauna were extinct within a century.

The bottom line was that hunting of the so-called megafauna by early humans in Patagonia were to primarily blame for the subsequent extinctions. But the humans required but a warm climate to help them to do the job.

CU-Boulder Senior Research Associate Jessica Metcalf, lead study author and a former postdoctoral researcher at ACAD, explains the study helps to clear up a muddy picture of now-extinct South American megafauna.

“The DNA and age of bones from South American megafauna showed the extinctions occurred long after human arrival there and coincided with climate warming,” says Metcalf, of the ecology and evolutionary biology department. “We found that members of the camel family, for example, considered resilient survivors of the last ice age, suffered huge losses in genetic diversity.”

The researchers studied ancient DNA they extracted from bones and teeth found in caves across Patagonia and Tierra del Fuego to trace the genetic history of the ice age mammals. As part of the research they also radiocarbon dated the samples, more than doubling the number of existing radiocarbon dates for Patagonia megafauna.

The earliest Americans are thought by most scientists to have traveled from northeast Asia over the Bering Land Bridge and into present-day Alaska some 16,000 years ago.

“The Americas are unique in that humans moved through two continents, from Alaska to Patagonia, in just 1,500 years,” says Professor Chris Turney of University of New South Wales, a study co-author. “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 different climate conditions.”

As part of the study the team amplified fragments of ancient DNA and pieced them together like a high-tech jigsaw puzzle to reveal genetic histories of the megafauna.

“This is a good example of how researchers from different disciplines and institutions can work together to answer long-standing and important questions in science,” says Metcalf. 

In 2014, Metcalf led a study on the genetics of the endangered greenback cutthroat trout, work that led to the re-introduction of the splashy fish back into its native waters.