New insight into the evolution of the vertebrate respiratory system and the discovery of unidirectional airflow in iguana lungs
The avian respiratory system appears strikingly distinct from all other animals. Purported key innovations underpinning avian patterns of airflow are an enclosed intrapulmonary bronchus, intercameral perforations, heterogeneous parenchyma; these traits allegedly coevolved with separation of the cardiac ventricle into right and left sides and are presumed to have been favored by selection because they facilitate high activity metabolisms. In contradistinction to these prevailing theories, here we show that unidirectional flow is present in the lungs of the green iguana, an ectothermic animal with low aerobic capacity, no intrapulmonary bronchus, and no intercameral perforations. This discovery indicates a transformation in our understanding of the evolution of the vertebrate respiratory system is needed.