I don't know that this "remained a mystery, until now" - an alternate (and I think more plausible) theory is that the higher oxygen content of the atmosphere in prehistoric times allowed for larger insects: http://insects.about.com/od/evolution/f/Why-Prehistoric-Insects-Were-So-Big.htm

The fact that we have children successfully begging for donations to cover their parents' healthcare expenses is proof that America has the best healthcare system in the world.