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An onscreen credit reads: "Made at Shepperton Studios Limited, Shepperton, Middlesex, England, and on location in the Canary Islands." The first scene begins with an unseen narrator explaining that it is a time of man's fear of the unknown, before the moon had first appeared. Following this, the rest of the film's dialogue is in an invented caveman language. According to the Hollywood Reporter review, the dialogue consisted of a "27-word vocabulary synthesized from Latin, Sanscrit and Phoenician."
An October 1968 Variety news item stated that When Dinosaurs Ruled the Earth was "being shaped" for distribution by the Warner Bros. subsidiary 7 Arts, which had at that time been renamed W7. However, all contemporary sources list only Warner Bros. Upon its release in England in October 1970, the film was titled When Dinosaurs Ruled the World and ran for 100 minutes. For its February 1971 American release, the film was cut to 96 minutes and retitled When Dinosaurs Ruled the Earth. Jim Danforth and Roger Dicken received an Academy Award nomination for Best Achievement in Special Visual Effects. Star Victoria Vetri was Playboy's 1968 Playmate of the Year, then using the name Angela Dorian.