This was the final film from the British production company, Amicus.
The armored creature that attacks McBride and his group in the cave near the end of the film was actually a model of the Late Permian reptile called Scutosaurus.
The seaplane bears the "Hat in the ring" insignia of the 94th Aero squadron from World War I. It was the first American unit to arrive in France during the war.
The replica Vickers Viking aeroplane built for the movie is currently on display at the Brooklands museum in Weybridge, Surrey.
Paintings by Frank Frazetta appear in the film either as murals on walls or as the inspiration for tableaux performed by the characters.