Implications of an avian-style respiratory system for gigantism in sauropod dinosaurs


  • ADF

    anatomical diffusion factor


    diffusing capacity

    equation image

    Membrane diffusing capacity

    equation image

    Physiological diffusing capacity for oxygen

    equation image

    Diffusion constant for oxygen (material property)


    Body mass [kg] or [ton], see text


    Change in metabolic rate (represented by equation image) for each 10°C change in TB


    Respiratory surface area


    Surface area


    Body temperature

    equation image

    Oxygen consumption rate

    equation image

    Maximum oxygen uptake capability (represents maximum possible metabolic rate)

    equation image

    Oxygen driving pressure: partial pressure difference between pulmonary capillary blood and lung air


    Harmonic mean thickness of air–blood diffusion barrier


In light of evidence for avian-like lungs in saurischian dinosaurs, the physiological implications of cross-current gas exchange and voluminous, highly heterogeneous lungs for sauropod gigantism are critically examined. At 12 ton the predicted body temperature and metabolic rate of a growing sauropod would be similar to that of a bird scaled to the same body weight, but would increase exponentially as body mass increases. Although avian-like lung structure would be consistent with either a tachymetabolic-endothermic or a bradymetabolic-gigantothermic model, increasing body temperature requires adjustments to avoid overheating. We suggest that a unique sauropod structure/function unit facilitated the evolution of gigantism. This unit consisted of (1) a reduction in metabolic rate below that predicted by the body temperature, akin to thermal adaptation as seen in extant squamates, (2) presence of air-filled diverticula in the long neck and in the visceral cavity, and (3) low activity of respiratory muscles coupled with the high efficiency of cross-current gas exchange. J. Exp. Zool. 311A:600–610, 2009. © 2009 Wiley-Liss, Inc.