If dinosaurs suddenly magically appeared today, could they

[raccoon]

breathe in today's atmosphere?

[TexasProgresive]

1. Probably but we might need to pump enough CO2

to support the great fern forests that supported the herbaceous dinos. Which gave big fat dino cows to the T-Rex and other predator dinos. This would be continuing the cycle as that giant bio-mass became the oil, gas and coal which we burn releasing more CO2 back in the the air. It's the cycle of life on a grand scale.

[OffWithTheirHeads]

2. but would T-Rex let Jesus ride on him?

[Romeo.lima333]

3. but they would be crushed by their own weight on today's earth

[Erich Bloodaxe BSN]

6. Wait, what?

Is that some sort of in-joke? The earth's gravitational field hasn't changed in any significant way since it formed. Yeah, we pick up a tiny bit of mass from meteorites, and lose a bit when things like helium escape the atmosphere, but overall it's basically constant.

[eppur_se_muova]

11. Yes, it's an in-joke. Some woo "scientist" suggested that Earth's gravity has varied over time ...

... so, you see, all those big giant dinosaurs weren't all that heavy. Gravity is stronger now, so we don't have such big animals anymore.

[Erich Bloodaxe BSN]

12. ahhhhh, ok :) nt

[rock]

4. I doubt it

So running after prey is out of the question. They would probably have to learn to ride motorcycles.

[Fumesucker]

14. Shouldn't be too difficult, they already ride bicycles..

[Thor_MN]

5. Depends what you mean by dinosaur.

If you are talking what most people mean, the really big ones, probably not.

The small ones would probably be OK.

[AlbertCat]

8. The small ones would probably be OK.

They are OK!

[Thor_MN]

9. Except that those are birds, which are descended from dinosaurs.

The question, in my opinion, although not overtly stated, was about dinosaurs being able to survive in today's atmosphere. The atmosphere has changed over the years and oxygen content now is less than in some eras. Modern birds have had the chance to adapt as the atmosphere changed, but would a dinosaur suddenly thrust into our atmosphere have issues?

I think it is likely that the biggest dinosaurs were able to get so big because they had more oxygen to breathe. They would probably struggle like we do at higher elevations.

[packman]

7. As I understand it, the Oxygen level was higher

way back when which helped the growth of the large beasties.

[muriel_volestrangler]

10. Probably

Different studies have come to different conclusions about the amount of oxygen in the atmosphere during different parts of the Mesozoic, with some concluding oxygen levels were lower than the current level (about 21%) throughout the Mesozoic,[8][9] some concluding they were lower in the Triassic and part of the Jurassic but higher in the Cretaceous,[10][11][12] and some concluding they were higher throughout most or all of the Triassic, Jurassic and Cretaceous.[13][14]

https://en.wikipedia.org/wiki/Mesozoic

We can adapt to the altitude at La Paz, which, at about 3500m, has about 2/3rds the oxygen (2/3rds of everything, of course) of sea level atmosphere. So even if they were used to more oxygen, they'd probably be able to breathe.

[NickB79]

13. And I'm sure there were mountain-adapted dinosaur species

Just as there are numerous species today that are adapted to living at high altitudes, I'm sure dinosaurs filled those niches as well, especially now that we're aware they were feathered and likely warm-blooded.

Even during the Cretaceous, when oxygen levels were highest, there would have been dinosaurs breathing much lower levels at high elevations, comparable to today's sea level content.

[Johonny]

15. Most likely yes

The pattern on bones suggests that dinosaurs had air sacks like birds. Air sacks allow for better extraction of O2 from the air. It is what allows birds to breath in atmospheric conditions where mammals struggle. Since the bone patterns of birds and bird like dinosaurs are so similar it is assumed that birds (who are a type of dinosaur) and dinosaurs had very similar lung physiology. There is of course another whole branch of dinosaurs that do not have evidence of air sacks in their bones. It is unclear if they had any air sacks at all. Would these dinosaurs have trouble in todays atmosphere. Well, these dinosaurs were more abundant the closer to modern times.

Peter Ward probably does a better job describing this than me. So I'll just recommend his book.

http://www.amazon.com/Out-Thin-Air-Dinosaurs-Atmosphere/dp/0309100615