Transformers Movie Concept Designs for Megatron Alt Mode

Essentially already confirmed by the leaked toy design pics comes the concept model sheet for the Megatron that shows alt mode and its various stages. Not sure what the differences are between the stages as they look identical to me. It also shows the design for his "Arm Cannon". Since none of the leaked designs before now have shown the traditional gun attached at the arm, I am guessing this is more like his arm transforms into the cannon.

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