Birds are unique among living vertebrates in possessing pneumaticity of the postcranial skeleton, with invasion of bone by the pulmonary air-sac system. The avian respiratory system includes high-compliance air sacs that ventilate a dorsally fixed, non-expanding parabronchial lung. Caudally positioned abdominal and thoracic air sacs are critical components of the avian aspiration pump, facilitating flow-through ventilation of the lung and near-constant airflow during both inspiration and expiration, highlighting a design optimized for efficient gas exchange. Postcranial skeletal pneumaticity has also been reported in numerous extinct archosaurs including non-avian theropod dinosaurs and Archaeopteryx. However, the relationship between osseous pneumaticity and the evolution of the avian respiratory apparatus has long remained ambiguous. Here we report, on the basis of a comparative analysis of region-specific pneumaticity with extant birds, evidence for cervical and abdominal air-sac systems in non-avian theropods, along with thoracic skeletal prerequisites of an avian-style aspiration pump. The early acquisition of this system among theropods is demonstrated by examination of an exceptional new specimen of Majungatholus atopus, documenting these features in a taxon only distantly related to birds. Taken together, these specializations imply the existence of the basic avian pulmonary Bauplan in basal neotheropods, indicating that flow-through ventilation of the lung is not restricted to birds but is probably a general theropod characteristic.

Pterosaurs, enigmatic extinct Mesozoic reptiles, were the first vertebrates to achieve true flapping flight. Various lines of evidence provide strong support for highly efficient wing design, control, and flight capabilities. However, little is known of the pulmonary system that powered flight in pterosaurs. We investigated the structure and function of the pterosaurian breathing apparatus through a broad scale comparative study of respiratory structure and function in living and extinct archosaurs, using computer-assisted tomographic (CT) scanning of pterosaur and bird skeletal remains, cineradiographic (X-ray film) studies of the skeletal breathing pump in extant birds and alligators, and study of skeletal structure in historic fossil specimens. In this report we present various lines of skeletal evidence that indicate that pterosaurs had a highly effective flow-through respiratory system, capable of sustaining powered flight, predating the appearance of an analogous breathing system in birds by approximately seventy million years. Convergent evolution of gigantism in several Cretaceous pterosaur lineages was made possible through body density reduction by expansion of the pulmonary air sac system throughout the trunk and the distal limb girdle skeleton, highlighting the importance of respiratory adaptations in pterosaur evolution, and the dramatic effect of the release of physical constraints on morphological diversification and evolutionary radiation.

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Over the past two decades, the development of methods for visualizing and analysing specimens digitally, in three and even four dimensions, has transformed the study of living and fossil organisms. However, the initial promise that the widespread application of such methods would facilitate access to the underlying digital data has not been fully achieved. The underlying datasets for many published studies are not readily or freely available, introducing a barrier to verification and reproducibility, and the reuse of data. There is no current agreement or policy on the amount and type of data that should be made available alongside studies that use, and in some cases are wholly reliant on, digital morphology. Here, we propose a set of recommendations for minimum standards and additional best practice for three-dimensional digital data publication, and review the issues around data storage, management and accessibility.

The skeletal and visceral kinematics of lung ventilation of the American alligator (Alligator mississippiensis) was examined using cineradiography, pneumotachometry, and intrapulmonary pressure recording. The respiratory pattern of A. mississippiensis is intermittent and diphasic. The inspiratory lung volume is retained during the non-ventilatory period through closure of the glottis. The aspiration pump of A. mississippiensis consists of multiple components: visceral movement, pubic rotation, gastralial movement, and costosternal movement, which vary independently in their contribution to lung ventilation. Vertebral flexion and extension is also observed, and may be a passive artifact of costal displacement. The amount of craniocaudal visceral movement during lung ventilation is variable, and can produce as much as 60% of the tidal volume. Pubic rotation is not directly coupled to visceral movement and contributes a relatively small percentage of the tidal volume, approximately 4% on average, as does vertebral flexion, which contributes less than 3%. Costosternal movement contributes the remaining majority of tidal volume, generally over 40%. The gastralia stiffen the abdominal wall and likely facilitate unified displacement of the abdominal wall. Tripartite ribs facilitate thoracic movement, allowing substantial excursion of the body wall. A relatively abrupt change in position of the vertebral parapophysis in the anterior thorax results in an increase in lateral rib movement in the posterior half of the thorax. The crocodylian aspiration pump appears to consist of a derived pelvic and diaphragmatic breathing pump combined with a basal costosternal and gastralial aspiration pump.