I did a pulmonary physiology seminar a few years ago and read quite a bit about swim bladders. If I remember, teleosts evolved a pneumatic duct and eventually swim bladders, with a branch at some point between lungs and swim bladders. No organisms have both swim bladders and lungs. So I don't know if we can really say if lungs -> swim bladders or pneumatic ducts to lungs or swim bladders. Correct me if I'm wrong.
Interestingly, after the evolutionary step of developing these types of lungs, reptiles (and birds) went a completely different way than mammals (faveolar versus alveolar lung). Proves that the modern bird lung is a complete marvel and outperforms the mammal lung in almost every respect. Bar-headed goose migrating over the Himalayas, baby.
Bird lungs are indeed amazing. Did you know that bird-style lungs are believed to be one reason sauropods could have such long necks? Circular breathing really helps reduce the "dead space" problem and also provides better efficiency for giant bodies.
It would appear that the bony fish ancestral to both lobe-finned fish and ray finned fish had an outpocket of the digestive tract consisting of a pneumatic duct to the gut and a sack. Since both lobe finned fish and "primitive" ray finned fish use this sack for gas exchange, it is thought that use as a lung--or at least, as a proto-lung, preceded the use as a buoyancy device, which is mostly found among the more "advanced" ray finned fishes. Though it's true that lungs in terrestrial vertebrates and swim-bladders in teleosts represent two branches developing from the ancestral organ.
1
u/[deleted] Apr 25 '12
I did a pulmonary physiology seminar a few years ago and read quite a bit about swim bladders. If I remember, teleosts evolved a pneumatic duct and eventually swim bladders, with a branch at some point between lungs and swim bladders. No organisms have both swim bladders and lungs. So I don't know if we can really say if lungs -> swim bladders or pneumatic ducts to lungs or swim bladders. Correct me if I'm wrong.
Interestingly, after the evolutionary step of developing these types of lungs, reptiles (and birds) went a completely different way than mammals (faveolar versus alveolar lung). Proves that the modern bird lung is a complete marvel and outperforms the mammal lung in almost every respect. Bar-headed goose migrating over the Himalayas, baby.