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.
Animals in decline
Animals in decline
1/8 Harbour seal (Phoca vitulina)
Where: Orkney Islands. What: Between 2001-2006, numbers in Orkney declined by 40 per cent. Why: epidemics of the phocine distemper virus are thought to have caused major declines, but the killing of seals in the Moray Firth to protect salmon farms may have an impact.
2/8 African lion (Panthera leo)
Where: Ghana. What: In Ghana’s Mole National Park, lion numbers have declined by more than 90 per cent in 40 years. Why: local conflicts are thought to have contributed to the slaughter of lions and are a worrying example of the status of the animal in Western and Central Africa.
3/8 Leatherback turtle (Dermochelys coriacea)
Where: Indonesia, Malaysia, Mexico, Costa Rica. What: Numbers are down in both the Atlantic and Pacific. It declined by 95 per cent between 1989-2002 in Costa Rica. Why: mainly due to them being caught as bycatch, but they’ve also been affected by local developments.
4/8 Wandering albatross (Diomedea exulans)
Where: South Atlantic. What: A rapid decline. One population, from Bird Island, South Georgia, declined by 50 per cent between 1972-2010, according to the British Antarctic Survey. Why: being caught in various commercial longline fisheries.
5/8 Saiga Antelope (Saiga tatarica)
Where: Kazakhstan, Mongolia, Russia, Turkmenistan, Uzbekistan. What: fall in populations has been dramatic. In the early 1990s numbers were over a million, but are now estimated to be around 50,000. Why: the break up of the former USSR led to uncontrolled hunting. Increased rural poverty means the species is hunted for its meat
6/8 Swordfish (Xiphias gladius)
Where: found worldwide in tropical, subtropical and temperate seas. Why: at risk from overfishing and as a target in recreational fishing. A significant number of swordfish are also caught by illegal driftnet fisheries in the Mediterranean
7/8 Argali Sheep (Ovis mammon)
Where: Central and Southern Asian mountains,usually at 3,000-5,000 metres altitude. Why: domesticated herds of sheep competing for grazing grounds. Over-hunting and poaching.
8/8 Humphead Wrasse (Cheilinus undulatus)
Where: the Indo-Pacific, from the Red Sea to South Africa and to the Tuamoto Islands (Polynesia), north to the Ryukyu Islands (south-west Japan), and south to New Caledonia. Why: Illegal, Unregulated and Unreported (IUU) fishing and trading of the species
“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."Reuse content