I've been thinking of this, and it hasn't been given much thought in the way of WMGs (wild mass guessings) or any forum thread, but would be it possible that there could have been an ancient Na'vi civilzation has come to my mind as of lately, mainly out of some things I've noted in the film and in the backstory.
It's noted that the Na'vi's society is either as old as or older than human civilzation. This causes some questions to be brought up, namely how could an entire society not change for some 10,000 plus years? My minor quibble about this would be that it does not seem natural for ANY kind of society, which has brought me to a certain theory I would like to make:
Sometime in the last 10,000 years or so, the Na'vi had a sufficiently advanced civilzation. It thrived but either died off slowly, possibily due to environmental factors (similar to what happened to the Mayan and Anazazi civilzations; they didn't die off, they stopped living in the buildings and building and mantaining temples and cities) or they were catastrophically destroyed (maybe the first Time of Great Sorrow?), to the point that the Na'vi just couldn't live that way. The Na'vi eventually became the Omaticaya and other Clans we saw in the movie (I don't know about other Clans out there, but I suspect that every Na'vi clan is unique in it's own way); the cities and temples were later lost to the growing rainforests and jungles. When the RDA came around, the ruins of the former civilzation were so overgrown and deterioated that no one can recognize them as viable ruins. Add to the fact that the RDA were more interested in mining unobtainium than they were finding ruins or studying the Na'vi, outside of the anthrologists and the scientists coming there; and you have to wonder what else is out there. There is just so much about the Na'vi we don't know outside of a few tools, weapons, and their language; we do not know a lot of their songs, their stories, their mythology outside of Eywa and the floating seeds.
My main thought is that the second movie will explore the Na'vi's culture more in detail than it did in the first film, also get into their history and Eywa.


