I don’t want to be too dogmatic about this claim, but Godzilla is unrealistic.  I don’t want to be too non-dogmatic about this claim either.  OK then, just how dogmatic should I be?  I have all sorts of reasons for thinking that skyscraper sized lizards or dinosaurs don’t actually exist.  Honestly, the most important of these is probably that none of the people who I imagine would know if they did exist seem to believe in them.  I never hear any mention of them in the news, in history books, etc, and I don’t see their effects in the national death statistics.  No industries seem to exist to deal with their rampages, and no oil or shipping companies lose stock value from lizard attacks.  Casually, at least, Godzilla attacks don’t seem like the sort of basic fact about the world that people could just overlook.  How confident should I be that Godzilla type creatures don't exist? 

I can also fairly easily recognize good biological reasons not to expect there to be giant rampaging lizards.  The square/cube law, in its many manifestations, is the most basic of these, but by itself is not completely decisive.  I can imagine physical workarounds that would allow sequoia giganticus sized reptiles, but not without novel bio-machinery that would take a long time to evolve and would surely be found in many other organisms.  I can even vaguely imagine ways in which biology might prove resistant to conventional military weaponry and ecological niches and lifestyles that might support both such biology and such size, though much of my knowledge of Earth’s ecosystems would have to be re-written.    For all that, if I lived in a world where essentially all authorities did refer to the activities of godzilla giganticus  I would probably accept that they were probably correct regarding its existence.  What should a hypothetical person who lived in a world where the existence of Godzilla type creatures was common knowledge and was regarded as an ordinary non-numinous fact about the world believe?

Godzilla would be considerably more perplexing than thunderstones, and would have to be considerably better documented to be credible.  Even with the strongest documentation I would have substantial unresolved questions, inferring that Godzilla’s native ecosystem must be quite different from any known (possibly inferring that the details are classified), and even wondering whether Godzilla was a biological creature at all as opposed to, for instance, a giant robot left behind by an advanced and forgotten civilization, a line of inquiry that would greatly increase my credence in secret history of all kinds.  For the most part though, I would probably go about life as normal.  Even Natural Selection, the most damaged part of my world-view, would endure as a great intellectual triumph explaining the origins of almost all of Earth’s life forms.  Only peripheral facts, such as distant history and the nature of some exotic ecosystems would be deeply called into question, and such facts are not tightly integrated with the broader edifice of science.  In a conversation with a hypothetical Michael Vassar who believed in Godzilla, the issue would typically not come up.  Science in general would not be called into question in my mind, but should it be?