Godzillafan1995-- I doubt that Darabont would change a key plot point.
Not only does the whole plot revolve around finding a Godzilla body. Not only does it provide Godzilla with a name, it explains the connection between Godzilla and the muto and explains why muto is a threat, why Godzilla and Muto fight.
To have the skeleteon be another giant creature would just be confusing. I'm going to say at this point, I'm 80% sure the script was real and I'm 90% sure this skeleton is of a Godzilla. To just have a third, odd creature in the film would make almost no sense and give no idea of how dangerous the muto are.
The script basically explains that Muto were mortal enemies of Godzilla's species and capable of taking a Godzilla down... I know a few things about story telling and if Muto is portrayed as being capable of killing Godzilla, it really hurts the suspense factor in the film.
But-- whatevs. When the film comes out, one of us is going to be jamming out to Mr. Bumpy's I was right and you were wrong song. Until then, lets just agree to disagree.
He is 350ft Tall people, those things on his neck ARE gills, and the Brazil photo is part of the final advertising design-- Deal with it.