 When Godzilla first rises from the ocean, the costume appears to be  the complete suit used in the prior film (Godzilla vs Mothra) which  features a longer and more reptilian looking head. This does not  match the head used for the monster throughout the rest of the film.  Toho commonly used older versions of their monster suits when  filming scenes that take place in water, in order to avoid wear and  tear on the new featured costume.