“About 300 million years ago, long before the first dinosaurs appeared, a different type of oversized critter inhabited Earth: giant insects. Scientists suspect bugs grew bigger then because the atmosphere contained more oxygen than it does now. For example: Wings of one ancient dragonfly measured almost as long, tip to tip, as a Little League baseball bat. Alas, the giant insects didn’t last, and a modern dragonfly can fit comfortably inside a Wiffle ball. In a new study, researchers say the reign of mammoth insects ended when hungry, flying predators came along about 150 million years ago.” (Source) To read more about prehistoric insects click here and here.