Unidirectional pulmonary airflow patterns in the savannah monitor lizard

The unidirectional airflow patterns in the lungs of birds have long been considered a unique and specialized trait associated with the oxygen demands of their volant lifestyle, endothermic metabolism and unusual pulmonary architecture; however, the discovery of similar flow patterns in the lungs of crocodilians indicates that this character is likely ancestral for all archosaurs, the group that includes extant birds and crocodilians as well as their extinct relatives, such as pterosaurs and dinosaurs. Unidirectional flow in birds results from aerodynamic valves, rather than from sphincters or other physical mechanisms, and similar aerodynamic valves appear to be at work in crocodilians. Due to anatomical and developmental similarities in the primary and secondary bronchi of birds and crocodilians, these structures and airflow patterns may be homologous. Thus the origin of this pattern is at least as old as the split between crocodilians and birds, which occurred in the Triassic; however...