An international team of scientists Wednesday announced the discovery in northern Colombia of fossil remains of the largest snake ever known to have existed. It was named Titanoboa cerrejonensis, meaning titanic boa from Cerrejón, the open-pit coal mine where the fossil was found.

Modern boas and anacondas, which average less than 20 feet in length and reach a maximum of 30 feet, have been known to swallow Chihuahuas, cats and other small pets, but this prehistoric monster ate giant turtles and primitive crocodiles. The fossil snake bones were found in an open-pit coal mine, along with its prey, which included turtles and crocodiles.

The 42-foot behemoth used to weigh more than a ton, according to an analysis in today's issue of the journal Nature. By studying fossilized sections of the snake's remains, scientists were able to estimate the size of the crocodile-consuming boa.

"This is amazing. It challenges everything we know about how big a snake can be," said herpetologist Jack Conrad of the American Museum of Natural History in New York, who was not involved in the research. The fossil "is the same as the largest Tyrannosaurus rex that we know of, although it only weighs one-sixth as much," he added.

Palaeontologists have long known that as temperatures go up and down over geological time, generally speaking, so does the upper size limit of cold-blooded creatures - or poikilotherms. This is because the metabolism of a poikilotherm is more or less controlled by the average temperature of its environment. Now, a snake this big could only live where the average temperature was between 30 and 34 degrees Celsius. So we gain info also about the climate at the time along the equator where the remains were found were once much balmier.

"Tropical ecosystems of South America were surprisingly different 60 million years ago," said Jonathan Bloch, a vertebrate paleontologist at the University of Florida, Florida Museum of Natural History, who worked with Head on the snake study. "It was a rainforest, like today, but it was even hotter and the cold-blooded reptiles were all substantially larger. The result was, among other things, the largest snakes the world has ever seen ... and hopefully ever will."

The giant reptile was a boine snake, a type of non-venomous constrictor that includes anacondas and boas. In the same fossil rainforest, the researchers also found giant sea turtles and crocodile relatives. That seems to fit with a general evolutionary drift toward "bigger is better," even if smaller has its advantages under other circumstances.

Previously, the largest known snake was Gigantophis, which lived about 39 million years ago in Egypt and was at least 10 meters long. The longest of the snakes currently living in the world is the reticulated python, measuring up to nine meters long.