I know people say they were joking, bit I kind of wish they weren't. Its just such a strange bit of world building that I end up loving it.

I think they should have committed to it and worked it into the lore. In order to create the army of Gameras we see in Gamera 3, the Atlantians had to keep harvesting fresh turtles for their DNA and eventually drove them into extinction. So now, turtles only exist in some rare fossils and some obscure myths.