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Did dinosaur 'emissions' help warm the prehistoric climate? (+video)

In a new study, scientists theorize that giant, vegetation-munching sauropods emitted nearly as much methane each year into the warm atmosphere as do all natural and industrial sources today.

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The connection between natural sources of methane – from the stomachs of cows and other ruminants to termites to swamp mud – already get factored in to modern greenhouse-gas calculations. Still, while Brontosaurus burps or emissions via other, more-egregious, violations of good manners trigger giggles, such calculations also suggest “that the feedback between animals and climate is a little tighter than we tend to think it is today,” Dr. Smith says.

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For Dr. Wilkinson and colleagues, it's all about the microbes in a ruminant's digestive tract.

The bacteria would have had a lot to process. Sauropods still hold the record for largest land animals in the planet' s 4.6 billion-year history. From nose to tail tip, they ranged in length from 20 feet to 112 feet. One member of the group, Amphicoelias fragillimus, is thought to have spanned 190 feet and weighed up to 135 tons.

Based on the fossil record, many of these creatures sported teeth better suited for stripping vegetation than for long sessions of contemplative chewing. No “stomachs” in these animals. Researchers speak instead of fermentation chambers.

For their estimate, Wilkinson and colleagues settled on 10 22-ton sauropods to every 250 acres of land. Increased warmth, moisture, and CO2 levels would have sustained far more vegetation than does today's climate. Given the behemoths' appetites, the team estimated that all the sauropods on the planet would have produced a combined 520 million tons of methane a year, compared with between 50 million and 100 million tons for today's ruminants.

Even if sauropod emissions only amounted to 260 million tons a year, the methane still would have had a significant climate effect, according to the team.

The work represents a “proof of concept,” Wilkinson and colleagues write in the paper detailing their results in Tuesday's issue of the journal Current Biology.

But it resonates with Smith. In 2010, she and colleagues from the Los Alamos National Laboratory and the Smithsonian Institution's National Museum of Natural History calculated that the relatively sudden die-off in large-bodied plant eaters – mastodons, giant sloths, and other large animals – within about 1,000 years of humans' large-scale arrival in the Western Hemisphere corresponded with a decline in atmospheric methane.

This decline came at the beginning of a cool period that lasted a little more than 1,000 years – called the Younger Dryas. Smith's team estimated that the loss of large plant eaters in North and South America could have accounted for at least 12.5 percent of the methane decline, and perhaps all of it.


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