Scientists say they have discovered fossil remains of a colossal prehistoric snake that once roamed the superheated Paleocene jungles of South America. The one-tonne Titanoboa cerrejonensis would have been more than 40 feet long and ten feet around at its thickest.

Investigating brainboxes say the mighty snake's huge size was made possible by the significantly higher temperatures on Earth 60m years ago. The size of cold-blooded creatures such as snakes is limited by the warmth of their environment.

"The size is pretty amazing," said David Polly of Indiana University. "We went a step further and asked, how warm would the Earth have to be to support a body of this size?"

Collaboration with Carlos Jaramillo of the Smithsonian Tropical Research Institute and Toronto paleontologist Jason Head produced an answer: 30°C to 34°C. This is noticeably hotter than present-day temperatures in Colombia, where the mega-snake fossils were found in a coal mine. Modern Colombian rainforest temperatures average out at 27°C, too cold for the monster snakes to survive.

"Tropical ecosystems of South America were surprisingly different 60m years ago," said Jonathan Bloch of Florida Uni, who found the fossils along with Jaramillo.

"It was a rainforest, like today, but it was even hotter and the cold-blooded reptiles were substantially larger. The result was, among other things, the largest snakes the world has ever seen."