DINOSAURS may have farted themselves to extinction, according to a new study from British scientists.

The researchers calculated that the prehistoric beasts pumped out more than 520 million tons of methane a year - enough to warm the planet and hasten their own eventual demise. Until now, an asteroid strike and volcanic activity around 65 million years ago had seemed the most likely cause of their extinction.

Giant plant-eating sauropods were fingered as the key culprits in the study, which appears in the latest edition of the journal Current Biology. An average argentinosaurus, weighing around 90 tons and measuring 140 feet (42m), chomped its way through half a ton of ferns a day, producing clouds of methane as the food broke down in its gut.

Professor Graeme Ruxton from St Andrews University in Scotland and co-researcher David Wilkinson, from Liverpool John Moores University, worked out just how much of the greenhouse gas the billions of dinosaurs would have generated during the Mesozoic era, starting 250 million years ago.

"A simple mathematical model suggests that the microbes living in sauropod dinosaurs may have produced enough methane to have an important effect on the Mesozoic climate," Wilkinson said. "In fact, our calculations suggest these dinosaurs may have produced more methane than all the modern sources, natural and human, put together."

The dinosaur output of 520 million tons is comparable to current natural and man-made emissions of the greenhouse gas, which scientists say is around 21 times more powerful than CO2 at trapping heat on Earth and causing climate change. Cows and other farm animals globally contribute up to 100 million tons a year of methane.