The Swimbladder as a Respiratory Organ in Lepidosteus

In the past there have been many papers presented which have given evidence pointing to a probable origin of air-breathing vertebrates from certain physostomous fishes. The animals to which these papers have referred, apparently have some organ capable of supplementing respiration in times of need. Several of the Dipnoi and Ganoids have been credited with this adaptation and therefore have been responsible for the transition of a large number of vertebrates from water to land. Such a change gives rise to the need for organs capable of respiring atmospheric air