On the origin of avian air sacs

@article{Farmer2006OnTO,
  title={On the origin of avian air sacs},
  author={C G Farmer},
  journal={Respiratory Physiology \& Neurobiology},
  year={2006},
  volume={154},
  pages={89-106}
}
  • C. Farmer
  • Published 1 November 2006
  • Biology, Medicine
  • Respiratory Physiology & Neurobiology
For many vertebrates the lung is the largest and lightest organ in the body cavity and for these reasons can greatly affect an organism's shape, density, and its distribution of mass; characters that are important to locomotion. In this paper non-respiratory functions of the lung are considered along with data on the respiratory capacities and gas exchange abilities of birds and crocodilians to infer the evolutionary history of the respiratory systems of dinosaurs, including birds. From a… 
Vertebral morphometrics and lung structure in non-avian dinosaurs
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Although fully avian lungs were a rather late innovation, it is quantitatively show that non-avian dinosaurs and basal dinosauriforms possessed bird-like costovertebral joints and a furrowed thoracic ceiling, which could have permitted high levels of aerobic and metabolic activity in dinosaurs, even in the hypoxic conditions of the Mesozoic, contributing to their successful radiation.
Pulmonary anatomy in the Nile crocodile and the evolution of unidirectional airflow in Archosauria
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The data indicate that the aspects of the crocodilian bronchial tree that maintain the aerodynamic valves and thus generate unidirectional airflow, are ancestral for Archosauria.
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Key events in archosaur evolution where respiratory physiology likely played a major role are highlighted, such as their radiation at a time of relative hypoxia following the Permo-Triassic mass extinction, and their evolution of elevated metabolic rates.
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    Journal of experimental zoology. Part A, Ecological genetics and physiology
  • 2009
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Several lines of evidence suggest that air sac-driven lung ventilation was primitive for Saurischia, and anatomical and evolutionary patterns of pneumatization in nonavian saurischian dinosaurs are diagnostic for specificAir sacs, including the cervical, clavicular, and abdominal air sacs.
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Comparing the thoracic rib and vertebral anatomy of Sinraptor, Allosaurus, Tyrannosaurus, and Deinonychus provides new evidence supporting the hypothesis of flow‐through ventilation in nonavian theropods, and concludes that an avian‐style pulmonary system was likely a universal theropod trait.
Postcranial Pneumaticity in Dinosaurs and the Origin of the Avian Lung
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Some of the diversity in gross anatomical features directing airflow in avian and non-avian reptiles and new insights into the cellular anatomy of the blood-gas barrier are reviewed, which in mammals is composed of specialized endothelial as well as epithelial cells.
Similarity of Crocodilian and Avian Lungs Indicates Unidirectional Flow Is Ancestral for Archosaurs.
  • C. Farmer
  • Biology, Medicine
    Integrative and comparative biology
  • 2015
TLDR
Results show thatAir sacs are not requisite for unidirectional flow, and therefore raise questions about the function of avian air sacs, and suggest a paradigm shift is needed in the understanding of the evolution of this character.
Cardio‐pulmonary anatomy in theropod dinosaurs: Implications from extant archosaurs
TLDR
The likely absence of bird‐like pulmonary function in theropods is inconsistent with suggestions of cardiovascular anatomy more sophisticated than that of modern crocodilians.
Chapter 13 – Respiration
TLDR
The unique structure of the avian respiratory system, which separates the functions of ventilation and gas exchange between large, poorly vascularized air sacs and small constant volume lungs, respectively, confers functional advantages over other vertebrates, especially in hypoxia.
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