Huh. I watched the original teaser trailer again and found something interesting.
Remember the scene when that one scientist who's face melted by the cobra/worm's acid came back and assaulted the crew? Well, if you watch the teaser again, you'll notice that Shaw is at the controls of the big eight wheeled land rover and is throwing it in reverse. And the shot of the two guys shooting at the mutated scientist? You can see Shaw and Weyland (in his supportive suit) behind them!
No wonder the scene felt so out of place. It was supposed to happen much later with the main characters involved! What the heck Scott?