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According to Variety, Cage is set to voice the role Crug, "a staunch traditionalist forced to lead his family beyond their comfortable usual haunts when an earthquake shakes things up."
On the other end, Reynolds is set to voice "yet-to-be-named" nomad whom "Crug meet up during their journey, that has a little bit more advanced ideas and thoughts than Crug is and ends up charming the clan, particularly Crug’s daughter. Trouble, naturally, follows."
Dreamworks is aiming to set this cavern picture set for 3D by March 2012. At the meantime, you may need some lesson on how to train the dragons first before going back in time of the cavern.