Science Commentary: unidirection flow in alligator lungs

15 January 2010.
Science Magazine Volume 327, No. 5963, pp. 338-340
DOI: 10.1126/science.1180219

Unidirectional Airflow in the Lungs of Alligators
C. G. Farmer and Kent Sanders

A new report published by two University of Utah biologists in Science Magazine provides experimental evidence for unidirection flow of inhaled and exhaled air in the lungs of alligators.

The researchers showed that even though living alligators (no scientific name provided, but abstract indicates American alligators Alligator mississippiensis were studied) lack the air sacs and pneumatic bones that allow living birds to efficiently take in oxygen, the soft-tissue arrangement nevertheless allows for a more circular breathing pattern than in other living air-breathing vertebrates (e.g. mammals have more of a 'tidal' breathing mechanism whereby incoming and outgoing air are mixed between the nose and the lungs).

While the new study provides fascinating possibilities for inferences to be made regarding the evolution of aerobic and metabolic efficiency of extinct archosaurs such as non-avian dinosaurs, the authors took it a little too far with their concluding "story" about how all archosaurs (including all dinosaurs) may have had this type of efficiency.

Given the evidence for unidirection air flow in lungs of alligators and birds, the concept of a phylogenetic bracket, or the use of extant organisms to infer morphology/behavior/physiology of intermediate extinct relatives, points to a possibility of non-avian dinosaurs sharing these features. However, it was done without undeniably strong evidence in this study; four individuals from a single alligator species (and please, even Wikipedia provides a scientific name for the American alligator in a non-scientific description!) were used in this study, to infer a common feature among animals spanning hundreds of millions of years (back to the Triassic).

Quite a stretch even to a non-science type, I would say.

I believe the main issue does not necessarily lie with the authors themselves. One should not expect the field of science to take giant leaps in every research paper; but nowadays researchers are often "forced" to make outlandish conclusions just to get into a more popular journal. More "Science" and less "Magazine", please?



220mya said...


I have to disagree with you here. Have you read the actual paper? The authors are very careful to indicate that this is a possibility. They only say "may have been present in their nondinosaur descendants". And I don't think that is unreasonable given that there is good evidence that all ornithodiran archosaurs had unidirectional lung flow, and the type of flow identified in Alligator doesn't leave any osteological traces. At the very least, I think you're being unfair picking on this paper. There are alot of other studies that make much more egregious claims in Science and Nature.

Zhijie (Jack) said...

Ok maybe the last part was more of a knee-jerk reaction; I did not mean to say that this paper embodies the story-telling spirit of many papers in the big journals. I did read through the paper, and the authors are more confident in the text and especially the last paragraph than in the abstract; they replaced "may have been" with "was" when discussing the presence of unidirectional flow in all archosaurs. Evidence for such a flow mechanism in both ornithodiran archosaurs and Alligator does make a stronger case for this characteristic being a common ancestral feature (symplesiomorphy) for all archosaurs, but the lack of osteological evidence to falsify this hypothesis still bothers means we cannot use the fossil record to test whether this explanation about the past is right/wrong. Now that is opening a bigger can of worms perhaps?

Thanks for the comment!

Spencer said...

More "Science" and less "Magazine", please?

I'd have to agree with that, Jack. As to the paper and your other feelings on it, I haven't a copy so can't decided for myself.

On the other hand, I understand your frustration. On a popular level, did you hear about the 2nd brain quote mining thing on the Discovery Channel? I saw that air and wasn't happy, even before I knew he was quote mined.

Shall we keep this out of our science and leave it to our entertainers?


P.S. My word verification is "unter." Ernest Untermann, anyone?