We've all read about how the oxygen crash in the Permian led to the dinosaur resurgence in the Jurassic. Here's the latest. It leaves out some steps but, Twitter.
First to explain is how anything survived the end of the Permian - at all. That's the era "when pigs ruled the world". I don't think that the complex bird respiratory-system evolved for the crisis. More likely immediate quick-fixes evolved for the problem, like barrel chests on Andean people. Of the whole reptile clade it wasn't just dino ancestors that survived; we're still here. As are crocodiles and lizards. Besides larger lung capacity I imagine iiiit allll gottt sloooowwwerrr.
I think dinosaurs gradually evolved throughout the Triassic, and only at the end beat out the rivals. [UPDATE 9/18: And there was another extinction just 19 My later.] Low metabolisms all 'round, I think, further implies slow evolution. It did take all the Triassic for something to break out the doldrums.
It seems the Triassic was low-oxygen for a long time. It follows that oxygen-hungry flying insects didn't do well, either. Otherwise I'd have expected flowering plants to appear on the scene earlier than they did.
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