Giant dinosaurs could have warmed the planet with their flatulence, say researchers.
British scientists have calculated the methane output of sauropods, including the species known as Brontosaurus.
By scaling up the digestive wind of cows, they estimate that the population of dinosaurs - as a whole - produced 520 million tonnes of gas annually.
They suggest the gas could have been a key factor in the warm climate 150 million years ago.
David Wilkinson from Liverpool John Moore's University, and colleagues from the University of London and the University of Glasgow published their results in the journal Current Biology.
Sauropods, such as Apatosaurus louise (formerly known as Brontosaurus), were super-sized land animals that grazed on vegetation during the Mesozoic Era.
For Dr Wilkinson, it was not the giants that were of interest but the microscopic organisms living inside them.
"The ecology of microbes and their role in the working of our planet are one of my key interests in science," he told BBC Nature.
"Although it's the dinosaur element that captures the popular imagination with this work, actually it is the microbes living in the dinosaurs guts that are making the methane."
Methane is known as a "greenhouse gas" that absorbs infrared radiation from the sun, trapping it in the Earth's atmosphere and leading to increased temperatures.
Previous studies have suggested that the Earth was up to 10C (18F) warmer in the Mesozoic Era.
With the knowledge that livestock emissions currently contribute a significant part to global methane levels, the researchers used existing data to estimate how sauropods could have affected the climate.
Their calculations considered the dinosaurs' estimated total population and used a scale that links biomass to methane output for cattle.