Paris - The mass extinction of large animals in the Pleistocene era caused today's dearth of soil nutrients, scientists said on Sunday, and warned of further damage if modern giants like the elephant disappear.
The Pleistocene epoch, which dated from about 2.6 million to 11 700 years ago, saw large animals dubbed megafauna take over domination of the planet from extinct dinosaurs, only to die out en masse themselves.
During their peak, much of the world resembled a modern-day African savannah.
South America, for example, was teeming with five-ton ground sloths, armadillo-like glyptodonts the size of a small car, and herds of elephant-like cuvieronius and stegomastodonts.
These megafauna, animals weighing more than 44kg, played a key role in fertilising soil far away from the areas near rivers where they fed - ploughing the nutrients they consumed back into circulation through their dung or their decomposing bodies when they died.
Large animals ate much more and travelled further than small ones, and were mainly responsible for long-distance fertilisation, said a study published in the journal Nature Geoscience.
"Big animals are like the nutrient arteries of the planet and if they go extinct it is like severing these arteries," said co-author Chris Doughty of the University of Oxford's Environment Change Institute.
"Because most of these animals went extinct the world has many more nutrient poor regions than it would have had."
Using mathematical models, researchers estimated the megafauna extinction reduced the dispersal of key plant nutrient phosphorus in the Amazon basin by 98%, "with similar, though less extreme, decreases in all continents outside of Africa", the only continent where modern humans co-evolved with megafauna.
Instead, the nutrients became concentrated near floodplains and other fertile areas.
The model used in the study will allow scientists to predict the effect of further extinctions, a fate the team said was "fast approaching many of the large animals that remain" today, mainly in Africa and Asia.