Arcouding to the public domain superhero wiki, the characters of Gorgo, Konga and Reptilicus are in the public domain. Claim that, since they first appeared in comic books and that copyright in those books have lapsed, that characters, not the movies, are now public domain. Is there any truth to this?

To our understanding this only means the comics themselves are in the public domain. The characters and the films they appeared in are not. Though don’t necessarily take our word for it, there’s probably someone else who knows much more about it.

Keeep in mind the Reptilicus comic had to be renamed Reptisaurus midway through due to Charlton Comics losing the rights to the name.