the oxygen levels and air density provide a bound on size. A general problem with all oxygen related explanations of giant griffinflies is the circumstance that very large Meganeuridae with a wingspan of 45 cm also occurred in the Upper Permian of Lodève in France, when the oxygen content of the atmosphere was already much lower than in the Carboniferous and Lower Permian. suggested that the lack of aerial vertebrate predators allowed pterygote insects to evolve to maximum sizes during the Carboniferous and Permian periods, maybe accelerated by an "evolutionary arms race" for increase in body size between plant-feeding Palaeodictyoptera and meganeurids as their predators. Families and genera These families belong to the order Meganisoptera: Aulertupidae Zessin & Brauckmann 2010 Kohlwaldiidae Guthörl 1962 Meganeuridae Handlirsch 1906 Namurotypidae Bechly 1996 Paralogidae Handlirsch 1906 These genera belong to the order Meganisoptera, but have not been placed in families: Alanympha Kukalova-Peck 2009 Asapheneura Pruvost 1919 Dragonympha Kukalova-Peck 2009 Palaeotherates Handlirsch 1906 Paralogopsis Handlirsch 1911 Schlechtendaliola Handlirsch, 1919 Typoides Zalessky 1948 Notes References Bibliography External links Phylogenetic Systematics of Odonata Carboniferous insects Permian insects Pennsylvanian first appearances Lopingian extinctions Extinct insect orders Odonatoptera