Or with our imagination ? After all since lungs are not too well preserved it is hard to study how they evolved. But we do have some hints. My question to you is how do you believe 'animal' to 'bird type' lungs would require a problem for evolution ?
As far as I understand birds use a far more effective exchange mechanism by breathing in through one and out through another port and they can do this at the same time. But I also understand that the bird lungs are morphologically the same, other than the buffering and port redirection.
For instance "theropods do have thin-walled, hollow bones (Gauthier, 1986)." Although there are no reports of pneumatopores connecting the "air sacpces" in the lung bones with the air sacs in the long bones of dinosaurs"
http://www.cmnh.org/fun/dinosaur-archive/1997Nov/msg00276.html
http://whfreeman.com/life/update/chap41.html has some cool pictures explaining this.
http://www.dinosauria.com/jdp/misc/lungs.html discusses some of the lungs/dinosaurs issues.
Are all the details known ? I don't think so, but has a convincing case been made that the evolution of bird lungs could not have taken place ? I don't think so either. It's an area of study. It appears to me that this is similar to the imho incorrect "irreducibly complex" arguments. We cannot imagine it, therefor it could not have happened.
Donald Howes: <<And the same with feathers, if they are only understandably useful as perfectly formed structures, then doesn't the idea that they formed slowly strange, in that they must have been advantageous at each stage? If we can't imagine how that would happen, isn't that a problem in evolution?>>
Or in our imagination. Plus your assertion that they are understandably useful as 'perfect structures' does not preclude that they are not useful or even disadvantageous at intermediate levels. Your assumption that they 'must have been advantageous at every stage' is incorrect as well.
http://www.talkorigins.org/faqs/feathers.html discusses a 'possible' path.
Donald Howes:<< I know that some will say that just because we can't imagine how it
happened, doesn't mean it didn't happen, but isn't it still a problem?>>
Sure, just not that devastating that it would require abandoning evolution.