Increased oxygen isn't going to make up for the fact that if these mega-saurs existed under Earth's present gravity they would be crushed as neither their bones nor muscles could handle the stress. To many, the size of these behemoths is clear evidence that Earth's gravity has not always been constant. That during the time of their existence, earth's gravity was significantly less than it is today. Of course, physicists who want to believe that gravity is a constant do not like these tidbits of data raising doubts about their precious constants, that are not constants.
Good post
Peace
#daemon-nice
Source on your claim that modern gravity woild crush dinosaurs?