When something the size of a large dinosaur has as small of lungs as they did and small nostrils, when they have to move much they can't get enough volume into their lungs without more pressure than what our atmosphere has.

If you were put in a sealed room with more oxygen in it than what is in our atmosphere and yet you only had a small straw to breath through and you had to run, you wouldn't get enough oxygen. You would need more pressure in the room to help push enough oxygen in for you to breathe right. Understand now?

Nyarlathotep

If it's possible for you to give me info on were I can research your claims I would appreciate it.

From what you are saying doesn't add up to me. I can understand that if you have a sealed containment system that you add anything else to it, that would increase pressure. But if you remove gas A, and replace it with the same amount of gas B, how does that increase pressure? You are aware that the Earth today doesn't have anything to hold in any extra pressure right? Trees do absorb gasses from the atmosphere right? And they release gasses back into the atmosphere right? I believe that it would be basically at the same rate. So if a tree died, and fell in the swamp, wouldn't the inability of it to remove anything more from the atmosphere, and the inability to release anything back into the atmosphere, keep it the same as the seconds before it dyed and fell into the swamp? Oh yeah they don't just fall over when they first die do they?

I explained in an earlier post. If you were to go into a sealed room and replaced one or more of the normal levels of another gas besides oxygen. And then you put oxygen into that room in an even amount as the gas you removed so the pressure was the same as before you swapped the gasses. And then you had to put a small straw in your mouth and plug your nose so you could only breathe through the straw. And then you ran around the room. You would not get enough oxygen, and you would have to yank the straw out so you could get enough oxygen in so you don't pass out.

It wouldn't be very hard for you to perform this experiment. All you would have to do is use room in your home. Get an instrument that you can read the atmospheric pressure, and large plastic sheeting, a vacuum cleaner, a bottle of compressed oxygen, and some tape.
Keep the vacuum outside the room with the hose in the room. Seal the room with the plastic and tape completely with you inside. Check the atmospheric pressure in the room. Now have someone turn on the vacuum (preferably by someone you trust, and if not take a knife in with you so you can cut your way out in the event of a problem. I'm not trying to have you commit suicide) until you notice a good difference in your breathing and or the pressure in the room. Then turn on the oxygen to bring the pressure back up to its original level, no more no less. Oh and you need a straw also. So place the straw in your mouth and tape your lips and nose closed. Duct tape works well. Now do some exercises that are cardiovascular in nature and you will see that it won't take long and you will find it hard to breathe. But then before you remove the straw, stick it over the outlet on the oxygen tank and turn it up until you get enough in that you feel you can breathe again. That will show you that you need more pressure to force it in the small opening. Like the small nostrils the dinosaurs have.

Please tell me that you get it now. I thought you were supposed to be the smart one?