Throwing out a kinda-obvious one here. The similarity in the two different aliens' physiology suggests they are different evolutionary offshoots; the Super 8 alien is to humans what the Cloverfield monster is to, say silverback apes. Thus, the Super 8 alien is the dominant sentient lifeform of that planet. The aliens' space program had them send Clovers into outer space, like we did with monkeys. One of them crash-landed into the ocean on Earth about a thousand or so years before Super 8 starts. The aliens finally gather up enough resources and send off one of their boys to check up on their spacemonkey's status, but drops the ball and ends up crashing his spacemobile just outside the small town of Roswell, New Mexico. The locals discovered the unconscious alien and drag it and the remains