DOI: 10.5061/dryad.h702r
title: Data from: Pulmonary anatomy in the Nile crocodile and the evolution of unidirectional airflow in Archosauria.

description: 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.
description: CT scan of Nile
 crocodile lungs (NNC5)This file includes the
 DICOM files for Crocodylus niloticus specimen number NNC5 (0.5kg). The
 lungs of NNC5 were inflated and scanned in a medical grade CT unit at the
 Royal Veterinary College, London at 90 kVp and 133MA with a slice
 thickness of 0.75 mm The lungs were excised and soaked in an iodine
 potassium iodide (I2KI) solution at concentrations varying from
 2.25%-3.75% (following the methods of Jeffery et al., 2001; reference
 available in the manuscript) prior to scanning.Crocodylus_niloticus_NNC5.zipMicro CT scan of Nile crocodile lung (NNC9)This file includes the DICOM files for the lungs of Crocodylus niloticus specimen number NNC9 (0.58kg). The lungs were excised and soaked in an iodine potassium iodide (I2KI) solution at concentrations varying from 2.25%-3.75% (following the methods of Jeffery et al., 2001; reference available in the manuscript) prior to scanning. The lungs of NNC9 were scanned in a micro CT unit at the University of Cambridge with a slice width of 0.0816 mm.Crocodylus_niloticus_NNC9.zipCT scan of Nile crocodile lungs (NNC6)This file includes the DICOM files for Crocodylus niloticus specimen number NNC6 (0.8kg). The lungs of NNC6 were inflated and scanned in a medical grade CT unit at the Royal Veterinary College, London at 90 kVp and 133MA with a slice thickness of 0.75 mm The lungs were excised and soaked in an iodine potassium iodide (I2KI) solution at concentrations varying from 2.25%-3.75% (following the methods of Jeffery et al., 2001; reference available in the manuscript) prior to scanning.Crocodylus_niloticus_NNC6.zip