" I next cut the wing Through the I humeri In Another fowl, and tying up the trachea, as in the cock, Found That the Air Pass to and from the bones by the canal in this bone "
(J. Hunter, 1758)
I think the only article in my undergraduate days I keep a copy of the paper is still consult the classic Schmidt-Nielsen on how birds breathe. This article (highly recommended!) Summarizes the characteristics of the respiratory system of birds, including the presence of air sacs and hollow bones connected to the respiratory system, plus the ability to air flow in one direction. For too long, it has been suggested that the particular characteristics of the respiratory system of birds they would particularly efficient to extract oxygen from the air, and even several authors suggested that these features could have been the result of natural selection pressures imposed by flight an energetically costly form of locomotion. However, a few years ago showed that the air sacs and hollow bones unidirectional flow of air is not unique to birds, but were also present in non-flying theropod dinosaurs, a fact that essentially led to reject the hypothesis of that these structures have evolved as adaptations related to flying (1 ). To make matters worse, last year published new fossil evidence indicates that members of the group of organisms closely related to dinosaurs (including birds), pterosaurs, also had hollow bones and air sacs ( 2 ) implying that the origin of these features probably came at a much earlier stage of evolution of the archosaurs (the group that includes birds, other dinosaurs, pterosaurs and crocodiles). Well, Science has recently published a finding that forces us to look further ago. The article shows that the unidirectional flow of air is not unique to birds, or the descendants of the most recent common ancestor shared by birds and dinosaurs: this seems to be also a feature of the respiration of the crocodiles!
And? Well, to me that itself seems a very interesting because it reinforces the idea that to understand the biology of any group of organisms, in this case birds, it is essential to know the evolutionary history of lineage to which belong. The respiratory system of this particular group may well have facilitated the evolution of flight (probably no coincidence that two of the three groups of flying vertebrates-birds and pterosaurs, are archosaurs), but clearly did not emerge as an adaptation for flight. And on the other hand, if the respiratory system and efficient highly modified with birds today have existed since the time when there was the most recent common ancestor of all archosaurs, other hypotheses about the history of life on Earth seem to start to be supported: it was proposed (4 ) that archosaurs survival in periods of low oxygen concentrations could have been facilitated by its highly efficient respiratory system and this could explain why this group was not as affected as many others in the mass extinction event of the late Permian ( 5 ).
In another tone, the finding that the crocodiles are unidirectional air flow as the birds is perhaps the closest thing to a crocopato evidence, the animal and now the actor Kirk Cameron ultracristiano and anti-evolution (and mentally retarded, according to this website ) suggested there should be if the theory of evolution were true. The next two images, which coincidentally my father sent me last night, came at the right time. If someone is sick enough to want to know the crocopato argument in detail, in the end there a (sad) video of Cameron.
Farmer, C., & Sanders, K. (2010). Unidirectional Airflow in the Lungs of Alligators Science, 327 (5963), 338-340 DOI: 10.1126/science.1180219
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