Huge plant-eating dinosaurs may have produced enough greenhouse gas by breaking wind to alter the Earth's climate, research suggests.
Like leviathan cows, the mighty sauropods would have generated enormous quantities of methane.
Sauropods, recognisable by their long necks and tails, were widespread around 150 million years ago.
They included some of the largest animals to walk the Earth, such as Diplodocus, which measured 150 feet and weighed up to 45 tonnes.
Scientists believe that, just as in cows, methane-producing bacteria aided the digestion of sauropods by fermenting their plant food.
"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," said study leader Dr Dave Wilkinson, from Liverpool John Moores University.
"Indeed, our calculations suggest that these dinosaurs could have produced more methane than all modern sources - both natural and man-made - put together."
The research is published in the journal Current Biology.
Methane is a more potent greenhouse gas than carbon dioxide, with a stronger ability to trap heat.
Dr Wilkinson and colleague Professor Graeme Ruxton, from the University of St Andrews in Scotland, began to wonder about Mesozoic methane while investigating sauropod ecology.
Research on a range of modern species has allowed experts to predict how much methane is likely to be generated by animals of different sizes.
The key factor is the total mass of the animal.
Medium-sized sauropods weighed about 20 tonnes and lived in herds of up to a few tens of individuals per square kilometre.
Global methane emissions from the animals would have amounted to around 472 million tonnes per year, the scientists calculated.
The figure is comparable to total natural and man-made methane emissions today. Before the start of the industrial age, about 150 years ago, methane emissions were around 181 million tonnes per year.
Modern ruminant animals, including cows, goats, and giraffes, together produce 45 to 90 million tonnes of methane.
Sauropods alone may have been responsible for an atmospheric methane concentration of one to two parts per million (ppm), said the scientists.
In the warm, wet Mesozoic, forest fires and leaking natural gasfields could have added another four parts per million.
"Thus, a Mesozoic methane mixing ratio of six to eight ppm seems very plausible," the scientists wrote.
"The Mesozoic trend to sauropod gigantism led to the evolution of immense microbial vats unequalled in modern land animals. Methane was probably important in Mesozoic greenhouse warming.
"Our simple proof-of-concept model suggests greenhouse warming by sauropod megaherbivores could have been significant in sustaining warm climates."