Wallace Beery portrays "Prof. Challenger," a peculiar but respected explorer who attempts to persuade his doubting colleagues about a plateau deep within the Amazon where dinosaurs still exist. Mocked and dismissed, he manages to obtain some financial support from "Sir John Roxton" (Lewis Stone), gathers a group of people, and they head back—vowing to bring undeniable evidence. The performances are acceptable; however, what truly distinguishes this film is the impressive stop motion animation. These effects are remarkable, although simple in design, and the size of the jungle environments might not seem entirely realistic. Nevertheless, the narrative gains momentum as the creatures battle one another and search for something to eat (one even appears to pause for a cigarette!). They manage to capture an injured dinosaur and bring it back—not precisely the sort of proof Londoners anticipated when it begins causing trouble in Piccadilly! This was a pioneering achievement, establishing a benchmark that later artists like Ray Harryhausen would expand upon.

Source on TMDB