Humans, not climate change, may have wiped out Australia’s giant kangaroos

The demise of most of Australia’s kangaroo species by 40,000 years ago may have had less to do with climate-caused dietary pressures and more to do with human hunters.

Dental analyses of ancient kangaroos reveal they weren’t such picky eaters as once thought, researchers report in the Jan. 10 Science. Instead, when it came to climate-related changes in food availability, the animals might have rolled with the punches, the scientists suggest.

Between 65,000 and 40,000 years ago, more than 90 percent of Australia’s large animal species went extinct. Over half were kangaroos. The primary suspects behind these extinctions were thought to be human hunters, who had arrived sometime between 70,000 and 50,000 years ago, and rapid changes in the climate, which may have dramatically reduced the animals’ dietary options.

But to paleontologist Samuel Arman of the Museum and Art Gallery of the Northern Territory in Alice Springs, Australia, and colleagues, the climate hypothesis didn’t make a lot of sense, at least when it came to kangaroos. The animals had weathered dramatic climate shifts before.

Australia’s kangaroos evolved between 20 million and 15 million years ago, when the continent was a lush rainforest. By 5 million years ago, the island had dried out — yet the kangaroos thrived, diversifying into new species and occupying numerous environmental niches that encompassed a wide variety of diets.

To assess the possible role of dietary restrictions, Arman and colleagues analyzed the teeth of 937 kangaroos, both fossilized and modern, studying tiny signs of wear and tear that point to what the creatures ate.

Previous studies of fossilized skulls and jaws suggested many ancient kangaroos consumed a restricted diet of tough plants, as opposed to the relatively supple grasses of modern-day kangaroos. But the new dental analysis of 12 ancient species and 16 modern ones suggests the long-gone kangaroos were generalists, consuming a variety of foods that would have helped them survive as the climate changed. That, the researchers say, points to human hunters as the more likely primary culprit for the animals’ demise.

It’s not the first time dental microwear analysis has called into question dietary assumptions of ancient creatures — including humans — gleaned from cranial analysis alone, the researchers say. That, they add, suggests it’s worth testing the teeth of other large Pleistocene mammals to truly understand how specialized their diets were — and whether loss of those diets led to their demise.