There is great debate as to whether or not large pterosaurs could fly or soar or even get off the ground. One question I have seen refers to the earth's density changing ie less density = less gravity and consequences. Space dust adding to density all sounds sensible

No one has made reference to surface gases being denser or lighter and drag ratios though I'm certain some one must have mentioned it. I have seen experiments carried out with humming birds in less dense atmosphere where they failed to fly effectively.

So was the atmosphere more dense than it is today as a result of say passing astroids knocking off atmosphere or causing different ratios of gas though I cannot yet imagine how.