Climate change, not human activity, was the likely culprit for megafauna extinctions.

An illustration of megafauna that roamed Africa.

While the current changes in the global climate are being caused by human activity, this isn’t the first time that the Earth’s climate has changed in dramatic ways. There have been numerous climactic shifts in Earth’s history, and they have been one of the leading causes of animal and plant extinction, and will likely continue to be.

Around 30,000 to 40,000 years ago, as humans were spreading around the globe, there was a mass extinction of sorts, wiping out the vast majority of the planet’s megafauna, large terrestrial creatures which evolved to deal with the harsh life of the previous ice age. In what is now Australia, for example, there existed “500-pound kangaroos, marsupial tapirs the size of horses and wombat-like creatures the size of hippos.” Now, none of those creatures exist.

For years, the prevailing hypothesis has been that humans “blitzed” Australia and wiped them out through over-hunting or changing land use.

New evidence, however, has taken humans off the hook.

Research has indicated that the animals couldn’t keep up with the changing climate: the Sahul, the region of land that is now Australia, Tasmania, and New Guinea, became too arid for them to survive. As the area became more arid, the variety of plants was reduced, leaving giant herbivores with little to eat and bringing them increasingly in competition with each other.

Believe it or not, the evidence for the researchers’ conclusion comes in the form of teeth.

Paleontologists studied the fossilized teeth of a variety of megafauna herbivores from the period where they were widespread—350,000 to 570,000 years ago—and compared them to the teeth of the megafauna that existed when they were in decline. The evidence they found shows that climate change had a significant impact on their diets, which may have been a major contributor to their extinction.

“We have found evidence that, as climate was changing and getting drier, animal diets were shifting dramatically,” said study director Larisa DeSantis of Vanderbilt University.

While humans did live alongside some of these creatures, and no doubt did hunt them or alter their territories through changing land use, it seems unlikely that they were responsible for the extinctions of all these creatures. The same is likely true of other parts of the world, like North America, where humans are generally blamed for the extinction of megafauna that once roamed the continent. Climate change might have had similar effects here as well.

“If climate change was a primary or contributing factor in their demise, as it appears, we need to pay more attention to how current levels of climate change are affecting animals today,” DeSantis said.