In Godzilla (1954), Dr. Yamane states Godzilla is a creature from the Jurassic period, of 2 million years ago, a wildly incorrect statement, even at the time. However, Godzilla Raids Again (1955) retcons this to an appropriate time for dinosaurs of 150 to 75 mya.

As a side note, Godzilla's adversary in this film is an Ankylosaurus, however, they again get the date wrong according to their contemporary science, as Ankylosaurus was already determined to be a late Cretaceous dinosaur, living around 80 mya to 66 mya, as opposed to 150 mya to 75 mya.