Image caption Strange days: The lizard was among a menagerie of animals inhabiting South East Asia during the Eocene

A newly described 6ft lizard that roamed South East Asia from 36-40 million years ago has been named after The Doors singer Jim Morrison.

The choice of name Barbaturex morrisoni is a play on the late frontman's epithet "The Lizard King".

Higher temperatures at the time are thought to have helped the lizard evolve to its unusual size.

The scientists were surprised to find that the reptile successfully competed for food against mammals.

You can't fully understand the evolution of ecosystems in the modern world without looking at the ones that preceded them Dr Jason Head, University of Nebraska-Lincoln

The study is published in Proceedings of the Royal Society B.

A team of palaeontologists analysed fossils of the giant reptile and discovered it was the largest plant-eating lizard to have ever existed.

It lived alongside other herbivorous and carnivorous mammals during the Eocene epoch. It was likely to have weighed about 27.2 kg (60 pounds).

Modern day lizards, like iguanas and agamids, are smaller than other herbivores and provide tasty meals for many larger predators.

But Barbaturex morrisoni was larger than most carnivorous mammals. And competition for resources did not appear to restrict its evolution into such a large lizard, the study found.

"Reptiles and mammals co-exist in most places on the Earth today. What is interesting about the Lizard King is that it was a large vegetarian co-existing and competing with other herbivorous mammals," co-author Prof Russell Ciochon, from the University of Iowa, told BBC News.

"Large lizards on the Earth today, such Indonesia's Komodo Dragon, and in the past, such as the late Cretaceous Chinese Chianghsia nankangensis and the Pleistocene Australian Varanus priscus, are all carnivores. These large carnivorous lizards were eating the mammals they co-existed with, not competing with the mammals.

"The large size of the Lizard King certainly protected it from many predators. But there is no doubt that it was hunted by mammalian carnivores of the day."

Lead researcher, Jason Head from the University of Nebraska-Lincoln believes his research will show how climate helped the reptile evolve.

Image caption Jim Morrison (far right - with band members) died in 1971

"We think the warm climate during that period of time allowed the evolution of a large body size and the ability of plant-eating lizards to successfully compete in mammal faunas."

"You can't fully understand the evolution of ecosystems in the modern world without looking at the ones that preceded them," Dr Head explained.

"By going back in time using the fossil record, we can find unique information on the origin of modern ecosystems.

"I was listening to The Doors quite a bit during the research," Head said. "Some of their musical imagery includes reptiles and ancient places, and Jim Morrison was of course 'The Lizard King', so it all kind of came together."

He added that it could be possible for such giant lizards to evolve again, but only if the climate was right.

Commenting on the work, Paul Barrett from the Natural History Museum, London, said that lizards were important herbivores in the past.

"Their existence seems to have depended on the climate being right to support large-bodied herbivorous creatures.

"Climate probably has a bigger influence on the evolution of plant-eating reptiles than we realised. It seems to be a more important factor than competition with other herbivorous mammals." he told BBC News.

Image caption Lizards today are generally smaller than other herbivores

"But we're changing the atmosphere so fast that the rate of climate change is probably faster than most biological systems can adapt to.

"So instead of seeing the growth and spread of giant reptiles, what you might see is extinction," he said.

That Barbaturex morrisoni lived during the late middle Eocene - a time when temperatures across the planet soared - is a very exciting finding, said Dr Darren Naish from the University of Southampton, who was not involved with the study.

"This was meant to be the time in history when all the modern mammal groups are starting to take off in terms of diversity and the evolution of modern body shapes.

"But in this fauna, which is well-known for early primates and early hoofed mammals, living alongside early members of the modern mammal lineage, are these giant lizards," he said.

Unanswered questions remain, say the researchers. Namely how long the lizards lived, how far they moved around the planet and the relationship their body size had to the changes in global temperatures.