"That's Sir John Roxton – sportsman." Cast Bestiary Prehistoric animals Agathaumas (seen in battle with Allosaurus and Tyrannosaurus and is based on a hypothetical restoration by Charles R. Knight,) Allosaurus (main carnivorous dinosaur seen, attacking Trachodon and Triceratops among others) Apeman (menaces the team of explorers) Brachiosaurus (seen during the volcanic eruption, one of which was attacked by a Tyrannosaurus) Brontosaurus (The main antagonist. After falling into a bog at the conclusion of a fight with an Allosaurus, one is captured and taken to civilization, where it escapes and terrorizes the city) Edmontosaurus (is preyed upon by the Allosaurus and called by synonym Trachodon or Anatosaurus) Pteranodon (the first prehistoric animal seen by the team of explorers) Stegosaurus (one disturbs the Agathaumas before the fight with the Allosaurus and Tyrannosaurus. It escaped the volcano eruption) Toxodon (a juvenile was seen being eaten alive by the Pteranodon. It is the only prehistoric mammal that is not a primate they find on the plateau) Triceratops (shown to be capable of handling an Allosaurus in battle) Tyrannosaurus (is seen to have little trouble bringing down Agathaumas, as well as having a taste for a Pteranodon that swoops in too close. One fights with a Brachiosaurus in the eruption scene. Like the film Fantasia, it is shown with three fingers.) Other animals on the plateau Mesopithecus live-acted by a Capuchin monkey Chimpanzee (helps the apeman antagonize the explorers) Crane Laughing owl live-acted by a horned owl Feathered Hylonomus Peccary Spider monkey Animals in the Amazon Anaconda Caiman or alligator Jaguar (stock footage) Peccary Python Scarlet macaw Spectacled bears (erroneously identified as "spectacle cave bears") Two-toed sloth (stock footage) Three-toed sloth Production This was the first feature-length film made in the United States, possibly the world, to feature model animation as the primary special effect, or stop motion animation in general. Willis H. O'Brien had previously, in 1918, worked on a film called The Ghost of Slumber Mountain that used stop motion photography. In The Lost World, he combined animated dinosaurs with live-action footage of human beings, but at first he was able to do this only by separating the frame into two parts (also known as split screen). As work went on, O'Brien's technique grew better and he could combine live-action and stop-motion footage in the same part of the screen. For the live action scenes, an open sewer behind the MGM studio in