The Pulmonary Anatomy of Alligator mississippiensis and Its Similarity to the Avian Respiratory System

Using gross dissections and computed tomography we studied the lungs of juvenile American alligators (Alligator mississippiensis). Our findings indicate that both the external and internal morphology of the lungs is strikingly similar to the embryonic avian respiratory system (lungs + air sacs). We identified bronchi that we propose are homologous to the avian ventrobronchi (entobronchi), laterobronchi, dorsobronchi (ectobronchi), as well as regions of the lung hypothesized to be homologous to the cervical, interclavicular, anterior thoracic, posterior thoracic, and abdominal air sacs. Furthermore, we suggest that many of the features that alligators and birds share are homologous and that some of these features are important to the aerodynamic valve mechanism and are likely plesiomorphic for Archosauria. Anat Rec, 2012. © 2012 Wiley Periodicals Inc.

[1]  O. Larsell,et al.  The embryology of the bird's lung. Based on observations of the domestic fowl. Part II , 1916 .

[2]  R. Boelaert.  Sur la Physiologie de la Respiration de L'Alligator Mississippiensis , 1942 .

[3]  H R Duncker,et al.  The lung air sac system of birds. A contribution to the functional anatomy of the respiratory apparatus. , 1971, Ergebnisse der Anatomie und Entwicklungsgeschichte.

[4]  C. Farmer.  Evolution of the vertebrate cardio-pulmonary system. , 1999, Annual review of physiology.

[5]  G. Mitchell.  On the origin of avian air sacs , 2006 .

[6]  J. Maina.  Development, structure, and function of a novel respiratory organ, the lung-air sac system of birds: to go where no other vertebrate has gone. , 2007, Biological reviews of the Cambridge Philosophical Society.

[7]  M. Benton,et al.  Superiority, Competition, and Opportunism in the Evolutionary Radiation of Dinosaurs , 2008, Science.

[8]  C. Brochu.  PHYLOGENETIC APPROACHES TOWARD CROCODYLIAN HISTORY , 2003 .

[9]  S. Perry.  Gas exchange strategy in the Nile crocodile: a morphometric study , 1990, Journal of Comparative Physiology B.

[10]  E. Hazelhoff.  Structure and Function of the Lung of Birds , 1951 .

[11]  J L Lehr,et al.  Inspiratory aerodynamic valving in goose lungs depends on gas density and velocity. , 1987, Respiration physiology.

[12]  C. Farmer,et al.  Unidirectional Airflow in the Lungs of Alligators , 2010, Science.

[13]  J. Maina,et al.  What it takes to fly: the structural and functional respiratory refinements in birds and bats. , 2000, The Journal of experimental biology.

[14]  M. Benton,et al.  The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida) , 2010 .

[15]  S. Nesbitt.  The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades , 2011 .

[16]  P. Sereno.  Basal Archosaurs: Phylogenetic Relationships and Functional Implications , 1991 .

[17]  S. Perry.  Gas exchange strategies in reptiles and the origin of the avian lung , 1992 .

[18]  C. Farmer,et al.  Reproduction: The Adaptive Significance of Endothermy , 2003, The American Naturalist.

[19]  E. Holmes.  A reconsideration of the phylogeny of the tetrapod heart , 1975, Journal of morphology.

[20]  K. Johansen,et al.  Physiological adaptations in vertebrates : respiration, circulation, and metabolism , 1992 .

[21]  C. Farmer.  Parental Care: The Key to Understanding Endothermy and Other Convergent Features in Birds and Mammals , 2000, The American Naturalist.

[22]  M. Norell,et al.  Extreme convergence in the body plans of an early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda) , 2006, Proceedings of the Royal Society B: Biological Sciences.

[23]  C. Farmer,et al.  The Provenance of Alveolar and Parabronchial Lungs: Insights from Paleoecology and the Discovery of Cardiogenic, Unidirectional Airflow in the American Alligator (Alligator mississippiensis) , 2010, Physiological and Biochemical Zoology.

[24]  D. Carrier,et al.  Evidence for Endothermic Ancestors of Crocodiles at the Stem of Archosaur Evolution , 2004, Physiological and Biochemical Zoology.

[25]  Fanny Moser.  Beiträge zur vergleichenden Entwicklungsgeschichte der Wirbeltierlunge. (Amphibien, Reptilien, Vögel, Säuger.) , 1902 .

[26]  D. Carrier,et al.  The evolution of pelvic aspiration in archosaurs , 2000, Paleobiology.

[27]  D. Carrier,et al.  Ventilation and gas exchange during treadmill locomotion in the American alligator (Alligator mississippiensis). , 2000, The Journal of experimental biology.

[28]  S. Perry.  Functional Morphology of the Lungs of the Nile Crocodile, Crocodylus Niloticus: Non-Respiratory Parameters , 1988 .

[29]  Franck Pichaud,et al.  Pax genes and eye organogenesis. , 2002, Current opinion in genetics & development.