Dinosaurs' Gas May Have Warmed the Ancient Air - Wall Street Journal

By ROBERT LEE HOTZ

Belching dinosaurs may have spewed so much methane into the air that it could have affected the climate tens of millions of years ago, when temperatures were twice as high as today, a team of U.K. scientists reported Monday.

The stomach gas released each year by a family of long-necked, plant-eating dinosaurs, which included the world's largest known land animals, may have equaled the total amount of methane produced every year today from all natural, agricultural and industrial sources, the researchers said Monday in the journal Current Biology. Methane, a greenhouse gas, is 23 times as effective at trapping heat in the atmosphere as carbon dioxide.

The new scientific work highlights the importance of wildlife, livestock, and other natural sources of greenhouse-gas emissions in shaping global climate.

As with cows, sheep and buffalo today, these plant-eating dinosaurs, known as sauropods, likely digested their leafy greens with the help of methane-producing microbes in their stomachs that fermented the plant matter after it was chewed and swallowed. Generally, other plant eaters and creatures that eat meat, including people, don't digest their food this way and pass gas that is mostly nitrogen and carbon dioxide, with trace amounts of methane and hydrogen.

Cattle belching and passing gas are considered a significant source of methane today, accounting for about 20% of U.S. methane emissions, according to the Environmental Protection Agency.

"It occurred to us that if people worry about cows and methane in the modern world, we ought to ask what these sauropods would have done," said ecologist David Wilkinson at the U.K.'s Liverpool John Moores University, who led the study. "We became interested in sauropods because they were so weird."

Indeed, the family of sauropod species, which roamed the planet for about 140 million years, included such creatures as the 100-ton Argenitosaurus, which was about 120 feet long, and Sauroposeidon, whose neck alone stretched for 40 feet.

For their calculations, the researchers used a standard formula normally used to measure emissions from modern livestock based on their numbers and eating habits. They gauged the extinct creatures' prodigious appetites and gas-producing capacity based on theories of dinosaur biomechanics and lifestyles.

By their estimate, these dinosaurs generated about 520 million tons of methane each year, the same as the total amount produced today from all sources. In comparison, cows, goats, giraffes and other such grazers that rely on microbes to aid digestion today produce between 50 million tons and 100 million tons of methane each year. The remainder of today's output comes from natural and industrial sources.

Dinosaur experts were skeptical. "Undoubtedly, biological gases like methane were produced" by sauropods, said Mark Norell, chairman of the Division of Paleontology at the American Museum of Natural History in New York, who wasn't involved in the project. "It is difficult to judge the volume of the gases," given the dearth of direct evidence about their feeding habits, digestion, typical herd sizes and the microbes themselves.

"There are just too many variables. All of them can vary by an order of magnitude," Mr. Norell said.

Mr. Moore and his colleagues acknowledged that they had no direct fossil evidence to support their conclusions.

"We had to rely on estimates, which are not straightforward for an extinct animal," Mr. Moore said. "This is probably impossible to prove, without a time machine, but we have shown that it is quite plausible that this could have been the case."

Write to Robert Lee Hotz at sciencejournal@wsj.com