Gator breath...

The little red feathered dinosaur pictured here, and all its feathered relations, have respiratory systems structured very differently from yours and mine. Their lungs are small, but are supplemented by a group of internal air sacs - 7 or 9 of them, depending on the bird. The air sacs are significant for a couple of reasons - they allow a more or less constant supply of air to the lungs, and they also result in the flow of air through the lungs being unidirectional. The lungs of birds don't have alveoli like ours. Instead, they contain large numbers of tiny,highly vascularized tubules known as parabronchi. The unidirectional flow of air through the parabronchi minimizes the mixing of oxygen-rich and oxygen poor air and allows birds to extract oxygen more efficientlly. It has long been thought that this respiratory anatomy was associated with the development of birds and thier aerial lifestyle. New information suggests that it may not be that simple. This new insight comes from those close relatives of birds - alligators.

Nothing startling there. We've long known that alligators are more closely related to birds than they are to the animals in the traditional Class Reptilia. That similarity, indicated by a number of anatomical characteristics such as skull structure and backed up by DNA evidence, has led to the recognition that the Class Reptilia is not a good, monophyletic taxonomic division. Unless birds are included. Tables of contents of zoology text books are about to change.

Still, a study just published in the journal Science provides interesting new insight. Turns out that the american alligator (Alligator mississippiensis) also has a unidirectional flow of blood through its lungs. Of course, alligators are notoriously poor fliers. The fact that this unique respiratory anatomy is shared between alligators and birds pushes the development of it further into the past. Back into the Triassic, some 250 million years ago, prior to the split of the lineage leading to birds and crocodilians. The authors speculate that this remarkable adaptation, rather than being associated with the development of flight, may have given the ancestors of both birds and alligators a competitive advantage in the dryer, less oxygen-rich environment at the time. It's likely that other relatives of birds and alligators breathed in much the same way. That would be the dinosauars.