It looks like there is a theory that dermal bone in early tetrapods was used this way, but it's still fairly speculative. https://www.nbcnews.com/id/wbna47176272
Breathing air came with challenges, though. A major one was getting rid of the air's carbon dioxide, which, when it builds up, reacts with water in the body and forms an acid.
Breathing air came with challenges, though. A major one was getting rid of the air's carbon dioxide, which, when it builds up, reacts with water in the body and forms an acid.