could not survive in the modern atmosphere. Other research indicates that insects really do breathe, with "rapid cycles of tracheal compression and expansion". Recent analysis of the flight energetics of modern insects and birds suggests that both the oxygen levels and air density provide a bound on size.

A general problem with all oxygen-related explanations of giant griffenflies is the circumstance that very large Meganeuridae (Arctotypus sp.) with a wingspan of 45 cm also occurred in the Late Permian