[aruanan]

Maybe the velociraptor wasn’t really that fast and everything was sort of a molassass world.

I was referring only to movement of animals, not to density of air. I remember asking one of Paul Sereno's grad students about the higher oxygen content way back then. He acknowledged it but didn't have much to say.

[Swordmaker]

Re: more oxygen

There are some data to indicate that there might have been a higher O2 component in the atmosphere than in modern times. This might explain the ability of the megafauna to breathe through long passages from nostril to lungs (40ft!) but hyperbariatric oxygen studies don’t seem to show any benefit for strength enhancement but do show greater stamina of the muscles for extended exertion.