Studies by Farmer and Sanders (2010) revealed that the lungs of the American Alligator--like those of birds, but unlike those of mammals--move air in only one direction during both inspiration and expiration through most of the tubular gas-exchanging bronchi (parabronchi). (In mammals, air moves tidally into and out of terminal gas-exchange structures, which are cul-de-sacs.) Given the phylogenetic relationship between crocodilians and birds, which are both archosaurs, Farmer and Sanders suggest that this air flow pattern may date back to the basal archosaurs of the Triassic and may have been present in their non-dinosaur descendants (phytosaurs, aetosaurs, rauisuchians, crocodylomorphs, and pterosaurs) as well as in dinosaurs, including birds (the avian dinosaurs).
