Interspecific variation in avian postcranial pneumaticity: A pilot study

Abstract

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.