of the flight energetics of modern insects and birds suggests that both the oxygen levels and air density provide an upper bound on size. The presence of very large Meganeuridae with wing spans rivaling those of Meganeura during the Permian, when the oxygen content of the atmosphere was already much lower than in the Carboniferous, presented a problem to the oxygen-related explanations in the case of the giant dragonflies. However, despite the fact that Meganeurids had the largest-known wingspans, their bodies were not very heavy, being less massive than those of several living Coleoptera; therefore, they were not true giant insects, only being giant in comparison with their living relatives. Lack of predators. Other explanations for the large size of Meganeurids compared to living relatives are warranted. suggested that the lack of aerial vertebrate predators allowed pterygote insects to evolve to maximum sizes during the Carboniferous and Permian periods, perhaps accelerated by an evolutionary "arms race" for increase in body size between plant-feeding Palaeodictyoptera and Meganisoptera as their predators. Aquatic larvae stadium. Another theory suggests that insects that developed in water before becoming terrestrial as adults grew bigger as a way to protect themselves against the high levels of oxygen. See also References Bibliography External links Picture of life sized model of Meganeura monyi made for Denver Museum of Natural History. Meganisoptera Pennsylvanian insects Gzhelian life Carboniferous invertebrates of Europe Paleozoic insects of Europe Fossil taxa described in 1885 Taxa named by Charles Jules Edmée Brongniart it:Meganeura