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Unidirectional breathing in archosaurs as described via Nile crocodile lungs



I haven't seen this hit the lists yet. PeerJ has a new article out on croc 
pulmonary anatomy and its place within Archosauria.

Pulmonary anatomy in the Nile crocodile and the evolution of unidirectional 
airflow in Archosauria

https://peerj.com/articles/60/

Abstract
 

The lungs of birds have long been known to move air in only one direction 
during both inspiration and expiration through most of the tubular 
gas-exchanging bronchi (parabronchi). Recently a similar pattern of airflow has 
been observed in American alligators, a sister taxon to birds. The pattern of 
flow appears to be due to the arrangement of the primary and secondary bronchi, 
which, via their branching angles, generate inspiratory and expiratory 
aerodynamic valves. Both the anatomical similarity of the avian and alligator 
lung and the similarity in the patterns of airflow raise the possibility that 
these features are plesiomorphic for Archosauria and therefore did not evolve 
in response to selection for flapping flight or an endothermic metabolism, as 
has been generally assumed. To further test the hypothesis that unidirectional 
airflow is ancestral for Archosauria, we measured airflow in the lungs of the 
Nile crocodile (Crocodylus niloticus). As in
 birds and alligators, air flows cranially to caudally in the cervical ventral 
bronchus, and caudally to cranially in the dorsobronchi in the lungs of Nile 
crocodiles. We also visualized the gross anatomy of the primary, secondary and 
tertiary pulmonary bronchi of C. niloticus using computed tomography (CT) and 
microCT. The cervical ventral bronchus, cranial dorsobronchi and cranial medial 
bronchi display similar characteristics to their proposed homologues in the 
alligator, while there is considerable variation in the tertiary and caudal 
group bronchi. Our data indicate that the aspects of the crocodilian bronchial 
tree that maintain the aerodynamic valves and thus generate unidirectional 
airflow, are ancestral for Archosauria.



Jason