Who put the Na'vi on Pandora?

I know that there are lots of important things going on but this issue needs clarification.

Pandora's dragonesque fliers, the Banshee and the gigantic Toruk are also bipeds. These raptor-like creatures have hindlimbs and membranous wings with a clawed digit. The odds of the human-like Na'vi and these bipeds evolving independently of the majority of Pandora's dominate hexapod species are vanishingly small, but if it is a conundrum in need of an explanation, I suspect they would have had to arrive at some distant era in Pandora's past.