Mammoths, sabre-tooth tigers, giant sloths and other ‘megafauna’ died out across most of the world at the end of the last Ice Age because the changing climate became too wet, according to a new study.
By studying the bones of the long-dead animals, researchers were able to work out levels of water in the environment.
And they found a link between the time large grassland animals and their predators became extinct in different parts of the world over a period of 15,000 to 11,000 years ago and a sudden increase in moisture.
This changed the environment from one dominated by grass to one more suited to trees, bogs and peatlands at the same time as human hunters moved in – creating a lethal “double whammy” that proved too much for many species.
The researchers warned that this process showed how vulnerable today’s large grassland animals could be to climate change, which will result in an increase in rainfall in some places.
One of the researchers, Professor Alan Cooper, of the Australian Centre for Ancient DNA at Adelaide University, said in a video: “What we have found by looking into the actual bones themselves is a signal of sudden environmental change just before they became extinct.
“We see water, moisture, everywhere, which we think is changing the vegetation patterns away from grass, which is what they want, towards trees. What we are really seeing is a double whammy, where the environment is suddenly shifting, the populations are in major trouble, and humans are turning up and hunting is taking off.”
It had long been a “big mystery” why Africa’s megafauna had remained when populations in the rest of the world died out, he said.
“The idea has been that they evolved with humans and were somehow used to them,” said Professor Cooper.
“What we see instead is, because there were no glaciers and large amounts of water to melt, grasslands were always present in Africa, so the animals never had the stress they had elsewhere.
“So it had nothing to do with being use to humans.”
He said the timing of the extinctions around the world, which hit South America first, then North America and then Europe, correlated with the increase in water.
“What it shows is climate change can have some quite large impacts across landscape-sized environments and that we should be quite worried about the warming that is going on now, the changes in water production, and about whether again we are going to see a suite of extinctions,” he said.
Elephants, rhinos and giraffes could all be at risk. “With added rainfall in these areas, we could actually see some quite major impacts on these populations, relatively quickly,” Professor Cooper said.
The international team of researchers, from the US, Russia and Canada as well as Australia, looked at levels of nitrogen isotopes from bone collagen that had been radiocarbon dated. This gave an indication of levels of moisture in the landscape, they said in a paper about the research in the journal Nature Ecology and Evolution.
“Grassland megafauna were critical to the food chains. They acted like giant pumps that shifted nutrients around the landscape,” said Dr Tim Rabanus-Wallace, also of Adelaide University.
“When the moisture influx pushed forests and tundras to replace the grasslands, the ecosystem collapsed and took many of the megafauna with it."