[prawks]

From what I understand, higher oxygen levels were only linked to large invertebrates, not dinosaurs:

Some paleontologists speculated that oxygen might be behind the evolution of huge dinosaurs, too, but the hypothesis has been totally undermined by evidence from the geological record and dinosaur anatomy. Geochemical evidence has shown that Jurassic and Cretaceous air contained about as much oxygen as today, if not a little less. More than that, the dinosaurs did not need increased oxygen to adequately nourish their bodies.

As part of their respiratory system, sauropods had a complex network of air sacs that gave them two advantages.

http://phenomena.nationalgeographic.com/2013/02/25/dinosaur-...