Crocodilians and birds are quite closely related to one another- both belong in the clade Archosauria. Although they seem to not have much in common, researchers from the University of Utah have done tomographic studies of alligator lung anatomy and found some striking similarities to that of its avian relatives. This is interesting because “Conventionally, the avian lung + air sac system is viewed as a cornerstone for the renowned aerobic capacity of birds, and as a very derived and unique respiratory system (Maina, , ). However, the discovery of unidirectional airflow in alligator lungs (Farmer, ; Farmer and Sanders, ) raises the possibility that many features are synapomorphic for archosaurs.” (Sanders+Farmer 2012). It turns out that Alligator mississippiensis, or the American Alligator, also possesses the unidirectional air sac/lung combination found in birds. It is somewhat more simplistic, which makes sense because the rest of crocodilian anatomy is also less derived from the common archosaurian ancestor. Why would crocodilians have this unique lung structure? According to the authors of this paper, “ It is not clear if unidirectional airflow is an exaptation, initially serving in cardiogenic flow during apnea (Farmer, ), an adaptation for expanded aerobic capacity during a time of environmental hypoxia, (Farmer, ; Farmer and Sanders, ), or if it serves another, unknown function”. Obviously, not much research has been done in this area yet. Perhaps there is more to come. If you want to read the article, click here. Most of the Results section is detailing lung anatomy, and is too dense even for a nerd like me. If you want to learn more, I recommend the “Functional Morphology of the Alligator Lung and Its Relationship With Other Crocodilians” section. Also, for a more detailed description (with diagrams!) of avian respiratory anatomy, click here.