I've also heard some contention over the ground up evolutionary theory for birds. Mainly that you don't evolve flight from jumping up, but rather from jumping tree to tree and gliding. I'm certainly not an expert in this but as a layman it does make sense to me, if you jump to escape a predator on the ground you inevitably come back down, but if you can make it to the next tree and your predator can't, that would indeed be a significant enough advantage to be passed down to your children. Seems easier to convert lizardy gliders like on the yi qi to wings too, rather than lizardy arms to wings.