The origin of lungs, the swim bladder as an oxygen-enriched diving system

The origin of the lung is the story of the origin of the swim bladder. So, what is the origin of the swim bladder? Historically, it has been assumed to be an adaptation for buoyancy. While this is true, there is a second function of the swim bladder that is not as widely recognized. The swim bladder is able to adjust the blood gas ratios (Hall, 1924), an adaptation that allows for increased vertical range of movement.