A giant ape that once roamed Asia as nature's closest version of a real King Kong is believed to have died out because it failed to adapt its diet to eat its greens.

The Gigantopithecus appears to have fallen victim to climate change as its favoured diet of forest fruit was wiped out by the ice age, according to a study published in the journal Quaternary International.

With only fragmentary fossil remains as guidance to its anatomical scale, researchers believe that the largest primate in history may have towered up to 3m tall and weighed as much as 500kg.

The ape, of which the closest modern cousin is the orangutan, flourished for hundreds of thousands of years in the then semi-tropical forests of South East Asia and southern China.

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There have previously been no clues as to the reason for its extinction about 100,000 years ago. Indeed, the only fossil records were four partial lower jaws, and perhaps a thousand teeth - they first turned up in the 1930s in Hong Kong where they were sold as "dragon's teeth".

But German scientists believe that they have now made a breakthrough after conducting new studies on variations in carbon isotopes in the enamel of teeth found in Thailand and China.

"Now, we are able to shed a little light on the obscure history of this primate," Professor Herve Bocherens, of the Centre for Human Evolution and Palaeoenvironment (HEP), at the University of Tubingen, told AFP.

The international team of scientists concluded that the ape was a forest-dwelling strict vegetarian. That diet dwindled as Earth was struck by a massive ice age during the Pleistocene Epoch, which stretched from about 2.6 million to 12,000 years ago.

"Due to its size, Gigantopithecus presumably depended on a large amount of food," said Bocherens. "When more and more forested area turned into savannah landscapes, there was simply an insufficient food supply."

Other apes, as well as early humans in Africa, survived by switching their diets to eat the leaves, grass and roots offered by their new environments.

Others have pursued a very different theory - most notably Grover Krantz, a professor in the United States who spent 30 years hunting the sasquatch, or "Bigfoot", the apelike creature which is supposed to haunt the forests of the Pacific north west of America.

In Big Footprints: A Scientific Inquiry into the Reality of Sasquatch, he suggested that about 2000 of the animals were survivors of Gigantopithecus that escaped extinction and migrated from Asia over the Bering straits.