Besides...many dinos were either a) carnivores or b) decendants of birds, not mammals or bovine
(a) Like modern ecosystems, I think dinosaur populations were bottom-heavy with herbivores, with quite a few insectivores and omnivores thrown in...and a smaller but substantial number of carnivores at the "top" of the food chain. Could be wrong. Correct me if I am.
(b) A bit backwards isn't it? Aren't birds thought to be descendents of dinosaurs...specifically therapods...making the dinos predecessors? Be that as it may, the fact that dinos were not mammals doesn't really say much about their flatulence one way or the other. Admitting to a lack of in-depth knowledge, I'd hazard a wild-assed guess that ruminants are ruminants the world over and may well fart pretty much the same. :glassesgr
As for paleo-greenhouse gasses, I seem to remember reading a while back that there's evidence indicating GHG levels tracked the temperature changes rather than vice versa. The gist was temp changes led to large changes in flora populations and perhaps large scale die-offs (and the resulting decomposition) that were responsible or contributed greatly. Vulcanism was cited as another major player during some periods, as well.
Edit to explain an inaccurate screw-up: I used "ruminant" when I probably should've said "grazers are grazers the world over" or some such. Technically speaking, ruminants (like cows) have multiple stomachs to digest tough vegetable matter and not all herbivores are ruminants. I don't know off the top of my head if any dinosaurs had multiple stomachs but I do understand that many (most?) herbivores had only one and that certain sauropods like Apatosaurus swallowed stones to aid in digestion.