Re: Na'vi anatomy
All flying creatures had two sets of wings as far as I can remember. But yeah, the second pair of some was small enough, so that can suggest that the third set of limbs might disappear in certain species one way or another.
The second pair of wings were their legs.
"There is no reason why good cannot triumph as often as evil. The triumph of anything is a matter of organization. If there are such things as angels, I hope that they are organized along the lines of the Maffia." - Winston Niles Rumfoord.