The avian respiratory system is very interesting because seperate regions are responsible for moving air in and out of the body (the air-sacs) and for gas-exchange (the lung). In addition air moves in the same direction through the gas-exchange regions of the lung on inspiration as it does on exhalation due to aerodynamic mechanisms (Bernoulli effects, jetting, etc.). We are investigating when, why, and how unidirectional airflow in lungs evolved by studying air-flow patterns in the lungs of the sister group to birds, the crocodilians.