Estimating methane emissions “for animals that are unlike anything living has to be a bit of an educated guess,” Dr. Wilkinson cautions in a prepared statement. The fossil record has allowed researchers to infer a great deal about the physiology and biology of sauropods. But estimates of their ranges and the number that could inhabit the same square mile of land require a lot of assumptions.
Still, the estimate “makes a lot of sense,” says Felisa Smith, a biologist at the University of New Mexico in Albuquerque. Dr. Smith and colleagues published an estimate two years ago of the possible climate effect from methane lost to the atmosphere as large plant-eating mammals roaming North and South America went extinct. Smith and others point to the large-scale arrival of humans from Eurasia around 14,300 years ago as the extinction's main cause.
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.
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.