In an interview with io9, concept designer Jordu Schell explained how he came up with the design for Avatar’s alien Na’vi. Starting the process he was given a rough sketch of what director James Cameron wanted the Na’vi to look like:

I knew that they were humanoid, that they were blue-skinned, that they were cat creatures, but that he very much wanted them to retain a humanoid, human-faced element to them.

And in the case of Neytiri, the main female character who ended up being played by Zoe Saldana, he says Cameron wanted her really sexy — in an exotic feline alien with blue skin and a tail sort of way.

Beyond that, Schell hints that there are still some otherworldly surprises hidden the Na’vi anatomy:

There are definitely some things about them that are more than just meets the eye … I mean, they don’t split open into gigantic demon creatures or something, but you’ll definitely see aspects of them that are unusual and cool and unique to this particular creature.

From Reelz Channel