title: Pulmonary anatomy in the Nile crocodile and the evolution of unidirectional airflow in Archosauria.
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.
authors: Department of Biology, University of Utah , Salt Lake City, UT , USA.
authors: Emma R
authors: ER
authors: Schachner
authors: John R
authors: JR
authors: Hutchinson
authors: Cg
authors: C
authors: Farmer
keywords: Anatomy; Bronchi; Crocodylia; Endothermy; Evolution; Lung; Pneumaticity; Respiration
references: J Exp Zool A Ecol Genet Physiol. 2009 Oct 1;311(8):629-46
references: 19810215
references: Ergeb Anat Entwicklungsgesch. 1971;45(6):7-171
references: 4258755
references: Anat Rec (Hoboken). 2009 Sep;292(9):1501-13
references: 19711481
references: Syst Biol. 1997 Sep;46(3):479-522
references: 11975331
references: Biol Rev Camb Philos Soc. 2006 Nov;81(4):545-79
references: 17038201
references: J Morphol. 1979 Sep;161(3):257-279
references: 30200690
references: Respir Physiol. 1979 Feb;36(2):143-54
references: 441570
references: Biol Rev Camb Philos Soc. 2012 Feb;87(1):168-93
references: 21733078
references: Physiol Biochem Zool. 2010 Jul-Aug;83(4):561-75
references: 20377411
references: Science. 2007 Apr 27;316(5824):557-8
references: 17463279
references: Respir Physiol. 1988 May;72(2):241-55
references: 3375616
references: Anat Rec (Hoboken). 2012 Apr;295(4):699-714
references: 22344783
references: Science. 2010 Jan 15;327(5963):338-40
references: 20075253
references: Respir Physiol. 1988 Jul;73(1):111-24
references: 3175353
references: Nature. 2008 Jun 5;453(7196):745-50
references: 18463632
references: Am J Physiol. 1985 Oct;249(4 Pt 2):R477-81
references: 4051034
references: J Exp Zool A Ecol Genet Physiol. 2009 Oct 1;311(8):611-28
references: 19204909
references: Integr Zool. 2006 Jun;1(2):80-5
references: 21395998
references: Evolution. 2011 Nov;65(11):3285-97
references: 22023592
references: Respir Physiol Neurobiol. 2006 Nov;154(1-2):89-106
references: 16787763
references: Physiol Rev. 2005 Jul;85(3):811-44
references: 15987796
references: PLoS One. 2009;4(2):e4497
references: 19223979
references: PLoS One. 2008 Sep 30;3(9):e3303
references: 18825273
references: J Exp Biol. 2000 Oct;203(Pt 20):3045-64
references: 11003817
references: J Exp Biol. 2008 Jan;211(Pt 1):66-78
references: 18083734
references: Anat Rec (Hoboken). 2011 Sep;294(9):1532-47
references: 21809455
references: Proc Natl Acad Sci U S A. 2007 Aug 7;104(32):13198-203
references: 17666530
references: J Morphol. 2006 Oct;267(10):1199-226
references: 16850471
references: Environ Health Perspect. 1997 Feb;105(2):188-200
references: 9105794
references: Syst Biol. 2003 Jun;52(3):403-22
references: 12775528
references: Respir Physiol. 1972 Mar;14(1):44-63
references: 5042157
references: Respir Physiol. 1972 Jul;15(3):384-97
references: 5050476
references: Science. 2005 Apr 15;308(5720):398-401
references: 15831755
references: Nature. 2005 Jul 14;436(7048):253-6
references: 16015329
references: Respir Physiol. 1978 Jul;34(1):61-81
references: 705077
references: PLoS One. 2012;7(3):e34094
references: 22470520
references: J Exp Biol. 2001 Jul;204(Pt 13):2313-30
references: 11507114
references: J Biomech. 2011 Jan 4;44(1):189-92
references: 20846653
references: Respir Physiol. 1971 Dec;13(3):319-29
references: 5158850