Just so we're all on the same page, you can disagree with the belief but still find it reasonable for someone else to think that way.
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Edited by Cerulean Velox: 6/3/2014 6:35:41 PMThe primitive mammals (who were small and rat-like at the time) couldn't evolve into bigger forms until their main natural threat (the dinosaurs) were gone. While the dinosaurs still existed, the mammals lived mostly underground and only came out at night. On the other hand, recent research has shown that the disappearance of the dinosaurs may not have been as sudden as originally thought.