I once developed that theory that egg stealers caused the decline of the dinosaurs. Mammals were already around at the time of the dinosaurs and because they bared their young live, they could avoid egg stealers. The warm blooded mammal could move about, even when it was cold. While the cold blooded dinosaurs, who needed more heat, became way too slow to avoid the egg stealers. You don't need a global disaster, just a cooling trend. The places where ancient lizards still remain in the world, are in the tropical areas; defense was better. Florida still has alligators, which date back to the dinosaurs, even thought the giant asteroid hit nearby.