According to The Illustrated Dinosaur Movie Guide: "Based on and idea by producer Merian C. Cooper. Historian Hiram P. Cobb believes there are Vikings still alive in a remote temperate region of the North Pole, known as the Blind Spot. With stunt pilot Jimmy Mathews, Cobb discovers the lost tribe, but their plane is crippled by a fifteen foot tall white snow eagle. After encountering a brontosaurus, triceratops, pterodactyls and a number of allosauri in the Valley of the Ancients, the Vikings mount their giant war eagles to defeat the German aerial armada of Zeppelins, which are attacking New York with a ray that neutralizes all electrical energy. A ten minute test reel was filmed by Willis O’Brien, with models built by Marcel Delgado, featuring a battle between a Viking-mounted giant eagle and an allosaurus. However, this proposed color project from MGM was eventually cancelled because of the outbreak of World War Two, when Cooper re-enlisted in the Army-Air Corps."