In the original trailer - there were "claws" in the last scene that matched neither Godzilla or flying Muto. They would match a mean caterpillar though.
I'm not saying I'm right. Just throwing the possibility out there.
@cspyro - good answers. Not sure I agree with them. But I definitely understand the overstating of the monsters size on the posters. HOWEVER - the monster whose spines break the water at the atoll - in scale to the island itself - lends itself to the scale of the original "monster behind transamerica building poster" more then anything else.
Conversely - the scenes in Hawaaii - Honolulu or where ever, he's again small statured. The latest poster of him behind a building with the soldiers on it - lend to a smaller size. But in the trailer - they shoot flares at something enormous.
With everything thats unbelieveably cool about thios marketing campaign - the seemingly shifting size scale continues to catch my, probably over critical, eye.