This 1961 release is believed to be the final wide general release feature to use stock footage from "One Million B.C." (1940) to supplement the special effects.
This film, with its monster movie title, was based on Jules Verne's 1877 novel "Hector Servadac" (aka "Career of a Comet" aka "Off on a Comet").
Some US advertising materials promoted the movie as having been filmed in "Monstascope", suggesting some kind of wide-screen process, but this was entirely misleading. In fact, the film was photographed with spherical lenses and projected at 1.85:1 - wider than regular Academy aperture (1.37:1), but not quite CinemaScope.