Yeah, those poor lizards whose footage would end up in countless other features throughout the proceeding years, including "Valley of the Dragons" which
is essentially "One Million B.C." but remove Victor Mature, Carole Landis & Lon Chaney, Jr (and add a bit of footage of Rodan!).
Was always curious why Hal Roach never approached Willis O'Brien to do the effects. My own theory was that when Roach produced "March of the Wooden Soldiers", which did utilize stop-motion, he probably found it time consuming and costly, so it was to be lizards with back fins that would rule this world (and strangely, garner an Academy Award for special effects!).