Life-forms from Pandora (the moon/planet that most of the movie is set on) have naturally occurring carbon-fibres laced throughout their bodies. This makes them very tough. I'm assuming that's why the Thanator could take that many shots to the head.Also, how does that thing take that many bullets in the face/mouth and keep on coming? Even if only a small percentage hit it still has to hurt!
the big monster really looks like a krootox, is GW will sue James Cameron for this one ?
I disagree. Kroot and krootox have a chicken/lizard look. They are rangy, scaly, with overlapping plates of armour, and a pointed beak. They are mostly bipedal, except for the Krootox, which seems to be a biped but hunched over like a gorilla with powerful shoulders and a "knuckle walk." They have also got quills, like a porcupine, and a tiny bit like the Predator.The big dog thing looks like a kroot/krootox - esque thing...strikingly, in my opinion. The dreds/flaps + the beak-ish maw are very similar.