I don't remeber the name of the video on youtube, but it showed a scientist theorizing that the earths atmospheric pressure was 7 times greater than it is today. Further speculating that the atmosphere was ripped away by an asteroid or the like. The cause of the exinction of the dinos was not enough O2 rather than an exinction event per se. Anyway following the change in atmospheric pressure life on earth came back in a smaller variety. Apparently greater pressure creates a perfect enviroment for life on earth. All things were bigger, trees, bugs, reptiles etc. To prove his theory he raises two piranah in barometric chambers. Fish#1 at current atmospheric presure and Fish#2 at a pressure 7X greater. Fish #1 was approximately 1lb while Fish#2 was like 5 lbs! Really huge. This could also explain the giant hominid fossils(steve quayle) found but suppressed. Just thinkin'