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Repeated evolution: air bladders or lungs in different groups of fishes evolved multiple times


Stuff happens ….

Several times throughout their radiation fish have evolved either lungs or swim bladders as gas-holding structures. Lungs and swim bladders have different ontogenetic origins and can be used either for buoyancy or as an accessory respiratory organ.

Therefore, the presence of air-filled bladders or lungs in different groups of fishes is an example of convergent (repeated) evolution.

https://www.ncbi.nlm.nih.gov/pubmed/15547792