A massive reduction in grasslands and the spread of forests may have been the primary cause of the decline of mammals such as the woolly mammoth, woolly rhino and cave lion, according to Durham University scientists.

The findings of the new study challenge the theory that human beings were the primary cause of the extinction of mammals through hunting, competition for land and increased pressure on habitats.

The research is part of the most comprehensive study to date of Northern Hemisphere climate and vegetation during and after the height of the last Ice Age, 21,000 years ago.