Study of sauropods indicated that their burps and flatulence were a major source of greenhouse gas.
LOS ANGELES - Dinosaurs' gassy guts may have contributed to global warming tens of millions of years ago, according to a study that finds a group of plant-eating dinosaurs could have produced about as much methane as all of today's natural and man-made sources of the greenhouse gas.
British researchers reported in Tuesday's edition of Current Biology that methane emissions from sauropods far outstripped those of today's cattle, goats and other cud-chewers.
Sauropods were a diverse bunch of plant-eating dinosaurs, known for small heads and giant bodies with long necks and tails. An average-sized sauropod -- such as Apatosaurus louisae -- could weigh 44,000 pounds.
Like many modern herbivores, scientists think, sauropods probably hosted a diverse community of microbes in their guts to help digest food, producing methane in the process. In cattle and other ruminants, that gas is released in the form of burps and flatulence.
Such emissions from cattle are considered a major source of the greenhouse gas, roughly 55 million to 110 million tons a year. Though carbon dioxide is more abundant in the atmosphere, methane is more than 20 times as effective at trapping heat.
The problem of cattle emissions prompted ecologist David Wilkinson of Liverpool John Moores University in England to consider climate-changing effects of sauropods. He and two other researchers used a formula from a study that linked body mass to methane emissions from guinea pigs and rabbits. The relationship is straightforward: The more body mass, the more methane produced.
They had to make some assumptions -- for example, that the ratio of body size to gas produced is the same for small and extremely large animals. "That's a slightly dodgy thing to do," Wilkinson said, "but in this case there's not any other option."
Researchers also used published dinosaur population estimates for the late Jurassic (about 161 to 145 million years ago).
The team concluded sauropods were probably producing about 572 million tons of methane per year -- more than five times as much methane as modern-day cattle and other ruminants. Today, worldwide emissions from animals and from such human activities as burning natural gas and collecting trash in landfills are estimated to produce 550 million to 660 million tons per year, researchers said.