Wallace Beery is the rather eccentric "Prof. Challenger" - an eminent explorer who tries to convince his justifiably sceptical peers of a plateau in the Amazonian jungle where there be dinosaurs... Derided and ridiculed, he secures some funding from "Sir John Roxton" (Lewis Stone), assembles a team and back they go - promising to return with proof positive. The acting is adequate - that's not what matters, really - it's the wonderful and fluent actions of the stop motion photography that makes the stand out. These effects are superb. Basic, sure, and the scale of the sets around them isn't likely to convince anyone - but the story really picks up pace amidst the jungle as these beasts fight each other and look for the odd snack or two for themselves (one even looks like he's stopped for a Woodbine!)... They manage to capture an injured one and take it home - not quite the proof the Londoners were expecting when it starts marauding round Piccadilly! It is groundbreaking, this - and set the standards for a world of creatives like Ray Harryhausen to build upon.
