Like modern-day ruminants, giant plant-eating dinosaurs likely had microbes in their guts that gave off large amounts of methane—a potent greenhouse gas even more effective at trapping heat than carbon dioxide. (Read about the greenhouse gas effect.)

Today cows, goats, sheep, giraffes, and other ruminants contribute to global warming by releasing as much as 50 million to 100 million metric tons of methane per year—a significant chunk of the 500 million to 600 million metric tons emitted annually, mostly due to human activity, according to the World Meteorological Organization.

The cud-chewing animals have large forestomachs packed with microbes that break down coarse plant material. The main byproduct of the process is methane—and it's got to go somewhere.

"Methane can come out of