Time travel, already a risky business, just got a whole lot scarier.

Scientists in America have unveiled a full-scale model of an ancient snake so large it could swallow a crocodile whole.

'Titanoboa' lived in what is now South America around 58-60m years ago, was 42 feet long and weighed more than a ton.

The massive animal was the largest snake ever known to have lived, and was more than twice as large as the current biggest specimen.

While not venomous, Titanoboa cerrejonensis was about to crush prey with a force of about 400lbs per square inch, which according to the BBC is the equivalent of lying underneath the weight of one and a half Brooklyn Bridges.

The terrifying snake's existence was confirmed after scientists excavated a coal mine in Colombia, known to be the site of one of the world's first tropical rain forests, and found its enormous vertebrae in the rock.

They also found fossils of a new species of turtle boasting a shell as thick as a dictionary - but said even that would be unlikely to stop the Titanoboa in its frankly unsettlingly huge tracks.

Jason Head, the lead author of the new species description in the journal Nature and research associate at the Smithsonian's National Museum of Natural History, said:

"The discovery of Titanoboa challenges our understanding of past climates and environments, as well as the biological limitations on the evolution of giant snakes." said Head "This shows how much more information about the history of Earth there is to glean from a resource like the reptile fossil record."

A full-scale model of the snake was unveiled at New York City's Grand Central station before the exhibit opens at the Smithsonian in Washington DC.