In the journal Current Biology, an analysis led by Dave Wilkinson of Liverpool John Moores University totes up the toots from the ancient plant-eating sauropods of the Age of Dinosaurs, and finds they likely produced even more methane than cows do today.
Sauropods, the long-necked and four-footed vegetarian jumbos of the Age of Dinosaurs, typically weighed more than 20 tons and seem to have lived in dense herds, the authors note, likely producing plenty of methane from their digestive processes to help keep temperatures warmer during their era.
Methane is a greenhouse gas more than 20 times more potent than carbon dioxide in its potential to retain heat in the atmosphere. "Today methane from livestock is a significant component of the global methane budget. Sauropod methane emission would probably also have been considerable," begins the study.
"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 Wilkinson, in a statement.
Unlike cows, the sauropods had a slower reptilian metabolism, but because there were so many of the beasts and because they lived in hothouse conditions on large, flat continents, the study adds their numbers up to find their likely emissions were about 573 million tons (520 million metric tonnes) of methane annually, "comparable to the total modern-day methane emissions," made by factories, livestock and other industrial processes. Cows worldwide only produce about one-eighth as much methane now as this estimated amount for ancient sauropods.
"Take together, our calculations suggest that sauropod dinosaurs could potentially have played a significant role in influencing climate through their methane emissions.," conclude the authors.
"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," says the study.
For some much-needed perspective, we asked National Oceanic and Atmospheric Administration scientist Ed Dlugokencky, a methane emissions expert, to comment on the gassy greenhouse dinosaurs. Here's his comment, by email:
"Based on some quick, simple calculations, scaling an estimate of the current number of cows globally (1 billion) at 500 kg/cow to 20,000 kg sauropods and current emissions from cows (~60 Tg CH4/yr) to 520 Tg CH4/yr, I estimated there would need to be 220 million sauropod dinosaurs. At 5 per square km, that would be 30% of continent area inhabited by the dinos.
If I did my estimates correctly, it seems to be plausible, but at the high end of what is plausible."
Another comment comes from geologist Jerzy Trammer of Poland's University of Warsaw, an expert on dinosaur biomass, who by email says of the study authors, "their hypothesis is likely."
Visit Science Fair for your daily dose of scientific news, from dinosaurs to distant galaxies. Science Fair is written by science reporters Dan Vergano and Elizabeth Weise and weather reporter Doyle Rice. Their subjects are often controversial -- and always fascinating -- be they stem-cell research, slime mold, or underground slush on Mars. More about the team