The avian bronchial tree has a unique and elaborate architecture for the maintenance of unidirectional airflow. Gross descriptions of this bronchial arrangement have traditionally relied upon dissection and casts of the negative (air‐filled) spaces. In this study, the bronchial trees of five deceased African grey parrots (Psittacus erithacus) were segmented from micro‐computed tomography (μCT) scans into three‐dimensional (3D) surface models, and then compared. Select metrics of the primary bronchi and major secondary branches in the μCT scans of 11 specimens were taken to assess left–right asymmetry and quantify gross lung structure. Analysis of the 3D surface models demonstrates variation in the number and distribution of secondary bronchi with consistent direct connections to specific respiratory air sacs. A single model of the parabronchi further reveals indirect connections to all but two of the nine total air sacs. Statistical analysis of the metrics show significant left–right asymmetry between the primary bronchi and the origins of the first four secondary bronchi (the ventrobronchi), consistently greater mean values for all right primary bronchus length metrics, and relatively high coefficients of variation for cross‐sectional area metrics of the primary bronchi and secondary bronchi ostia. These findings suggest that the lengths of the primary bronchi distal to the ventrobronchi do not preserve lung symmetry, and that aerodynamic valving can functionally accommodate a wide range of bronchial proportions.

The morphology and function of the avian respiratory system has been studied and debated for over a century due to its distinct features, such as: unidirectional airflow, aerodynamic valves, and a volume‐constant lung ventilated by non‐vascularized, compliant air sacs. Intra‐ and interspecific variation in the shape, size, and number of avian bronchi and ventilatory air sacs has been described from gross dissections and latex injections, but little has been done to describe the three dimensional (3D) morphology and variation of the avian respiratory system in situ, largely due to the destructive nature of dissection. This research aims to generate a detailed anatomical description and 3D digital models of the lower respiratory system of the African grey parrot (Psittacus erithacus). Four micro‐computed tomography (micro CT) datasets of deceased P. erithacus specimens were segmented to produce 3D tetrahedral surface meshes of the pulmonary tree, lung surfaces, air sac surfaces, and skeleton. The anatomical models were then validated via latex injections. Bronchial tree measurements of P. erithacus (n=8) were collected for intraspecific and interspecific comparisons with two other well‐studied archosaurian taxa: the ostrich (Struthio camelus, n=10) and the American alligator (Alligator mississippiensis, n=10). Similarities in the relationships between the carina and the first four large secondary airways of the bronchial tree suggest a role in maintaining unidirectional airflow patterns in these taxa that would have been present in a common ancestor. In some P. erithacus specimens, the cervical air sacs were found to have a broad, thin, and sub‐sternal expansion that extended caudally to encapsulate more than half the ventral abdominal viscera. In another specimen, the right and left abdominal air sacs merged along the midline to form a single, common abdominal sac. These results suggest that the shape and extent of the air sacs in P. erithacus are more variable than previously described for other avian taxa. The models, which will be made available as a detailed 3D digital anatomical atlas through the Grey Parrot Anatomy Project, will likely become an invaluable resource to avian veterinarians for surgical planning.Support or Funding InformationAssociation of Avian Veterinarians (AAV) Research Grant AwardThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The avian respiratory system is composed of a unidirectionally ventilated, volume‐constant gas‐exchanging lung, and a series of compliant, flexible air sacs. Diverticula from the lungs and air sacs invade adjacent bone and create air‐filled cavities within the skeleton through the process of pneumatization. While previous studies have addressed the presence or absence of pneumatic bones in multiple species, the pattern of pneumatization has been vaguely generalized with respect to which lung elements are responsible for pneumatizing different skeleton regions. Here, we aim to address which components of the avian respiratory system are pneumatizing each component of the postcranial skeleton and how the patterns vary between different taxa. Computed tomography (CT) and microCT data are used to visualize the pneumatized bones and to segment 3D digital surface models of the skeletal and respiratory systems. Specimens used in this study include the African grey parrot (Psittacus erithacus), ostrich (Struthio camelus), red‐tailed hawk. (Buteo jamaicensis), and tundra swan (Cygnus columbianus). We found substantial differences in the pneumatization patterns between the birds. In all taxa examined, there is an extensive supramedullary diverticulum that travels through the vertebral canal which directly pneumatizes each vertebra in the parrots but does not contribute to any pneumatization in the swan or hawk. The sacral, pelvic, and femoral elements are pneumatized solely by pelvic diverticula in the ostrich, but predominantly by the abdominal sacs in parrots. These data indicate that the pneumatization patterns in birds are highly variable and warrant further study.

Innovations in three‐dimensional (3D) imaging and segmentation have facilitated unprecedented levels of anatomical investigation into the detailed structures of the respiratory system that are often difficult to study in situ. Recent hypotheses of homology between crocodilians and birds have facilitated quantitative comparative analyses of bronchial trees and in situ models reveal new complexities in the relationship between the respiratory and skeletal systems. Here we quantitatively compare the bronchial trees of two crocodilians, the American alligator (Alligator mississippiensis) and Cuvier’s dwarf caiman (Paleosuchus palpebrosus) with select birds, including the ostrich (Struthio camelus), the African gray parrot (Psittacus erithacus), and the red‐tailed hawk (Buteo jamaicensis). Notably, the relative distances from the carina to the secondary bronchi measured are conserved, indicating a possible ancestral or constrained trait. With respect to interspecific avian comparisons, we found grossly observable variation within a single taxon in air sac morphology (e.g., P. erithacus), as well as substantial differences between the individual taxa via segmented surface models – particularly in the expansions of the interclavicular sacs, the extent of the diverticula, and the size of the abdominal sacs. Furthermore, we found that specific sac contribution to postcranial pneumatization varies substantially across our dataset. Individual specimens imaged for this study also revealed multiple pathologies, including scoliosis, foreign objects inside the animals, and broken bones, which have been incorporated into the anatomical models for clinical surgical atlases that are under development. While these data are preliminary, they provide a framework for larger scale comparisons and hypotheses of the ancestral archosaurian pulmonary system.