London, Dec 16 (ANI): It took nothing more dangerous than trees to drive the biggest mammals, Woolly mammoths to extinction, a new study has revealed.

The finding was based on a study, led by Professor Adrian Lister, a palaeobiologist at University College London, which found that forests gradually replaced the extensive areas of frozen grassland on which mammoths thrived, leaving the animals nothing to eat.

Woolly giants were grazers of the frozen grassland who weighed eight tons and reached 11ft tall.

Their tusks were up to 11ft long and they used them to clear snow. These mammals ate more than 300lb of grass a day.

Their closest living relative is the Asian elephant.

Lister claimed that rather than being wiped out by human hunters, the giant creatures were doomed by the spread of forests around the world at the end of the last ice age 10,000 years ago.

In the study Lister, with colleagues at the Natural History Museum and the Royal Holloway in London, analysed hundreds of mammoth fossils, extracting and comparing DNA sequences.

The analysis on the DNA extracted from hundreds of fossils revealed that the genetic differences between individual mammoths were so slight that the animals were unable to adapt to the changes in their environment.

“The DNA we have been able to extract from mammoth bones is like a clock and allows us to trace the evolutionary story in great detail now,” the Telegraph quoted Lister, as saying.

“In the middle of the last ice age, around 30,000 years ago, there were millions of mammoths roaming over a huge area.

“Around 20,000 years later there were hardly any left. As the forests moved in, the mammoths were pushed out of their normal habitat. These animals are mostly governed by vegetation rather than climate and so they were squeezed into very small populations as the forests took over the cold grasslands.

“I don’t think that people played a major role in wiping them out, although they may have pushed those final populations over the edge. The major impact factor was the change in the vegetation from grassland to trees, he added.

Richard Firestone, of the Lawrence Berkeley National Laboratory said: These large animals were particularly exposed to the shockwave produced by a large impact and had few places of refuge where they might have survived.

“There are probably strong parallels to the demise of the dinosaurs, he added.

Prof Lister will present his findings at the annual meeting of the Palaeontological Association in Sweden. (ANI)