If you studied animal form & function in year 12, you may well have looked at gas exchange systems. Most first-year bio courses will build on that, & at Waikato we introduce a whole range: skin surface, external & internal gills, the tracheal system in insects, & lungs. Including bird lungs.
Now, bird lungs are cool - they're really rather small relative to the animal's size, tucked away at the front end of the body cavity. And they're quite unlike our own lungs in the way they operate. Ours work on a tidal flow system - but birds have a one-way flow that allows them to maximise their extraction of oxygen from the air that they breathe. And birds evolved from a lineage of dinosaurs - so what, if anything, can we infer about dinosaur lungs?
Quite a lot, it seems :-) I've just happened across a post by PZ Myers, on Pharyngula, in which he looks at this very question. While the lungs and their interconnecting air sacs wouldn't fossilise, nevertheless they leave evidence of their presence in the organism's bones. The post includes some excellent illustrations & the comments thread is also well worth a read, not least for the way that it shows how scientific arguments play out.