Oxygen levels of the Mesozoic - what were they like?

[Infinity Blade]

It looks like there's some uncertainty over what oxygen levels during the Mesozoic era were actually like. Id est, higher, lower, or the same as modern pO₂ concentration (which is ~21%), and at what points. Just looking at Wikipedia's page and references for the Mesozoic is enough to tell you that, never mind if you underwent an extensive overview of as much literature as you could find on the subject. Even very recently, the Mesozoic is apparently still considered a rather hypoxic era (and relate this to the evolution of the avian air sac system; Brocklehurst et al. 2018).


So let's discuss Mesozoic oxygen levels here.

[dinosauria101]

^I don't mean to be 'that guy', but doesn't this belong in the zoological section?

[Infinity Blade]

When the main topic is about oxygen? I don't see why it has to, although you could relate this to animals.

[dinosauria101]

Eh, I suppose you've got a point.

Regardless, would there have been anything to suggest it was significantly different from today? There weren't any giant bugs or anything like that

[theropod]

Absence of gigantism in insects is probably a good indicator oxygen levels weren't extremely high, but they must have fluctuated throughout earths history, yet giant land arthropods are only really a thing in the carboniferous.

[dinosauria101]

^And I'm guessing lower oxygen levels would've meant less biodiversity? In that case, I think it's reasonable to conclude the oxygen levels of the Mesozoic were close to today's oxygen levels

[creature386]

I suppose most of you are already familiar with this, but in case not.
en.wikipedia.org/wiki/Geological_history_of_oxygen#/media/File:Oxygenation-atm-2.svg
So, there is a range of estimates for Mesozoic oxygen. According to the lower range, oxygen levels in the Mesozoic were lower than today. According to the higher range, they were mostly higher with a peak near the time the dinosaurs went extinct.