Interesting!
There's some evidence (https://geology.com/usgs/amber/) that oxygen levels were considerably higher during the cretaceous than current times. It's possible these higher levels enabled both giantism (some dinosaurs were *big*) and flight - particularly for large insects relying on diffusion down blind-ended 'trachaea' to support flight muscles. For example, there are fossils of dragonflies the size of current seagulls. This would have meant more forest fires - and there's also evidence that even marsh plants were more 'fireproof' (higher levels of lignin, first branches high above the ground).
I have to wonder if mammalian flight also predates the C-T 'boundary'.