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

Authors


  • ADF

    anatomical diffusion factor

    D

    diffusing capacity

    equation image

    Membrane diffusing capacity

    equation image

    Physiological diffusing capacity for oxygen

    equation image

    Diffusion constant for oxygen (material property)

    M

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

    Q10

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

    SR

    Respiratory surface area

    S

    Surface area

    TB

    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

    τh

    Harmonic mean thickness of air–blood diffusion barrier

Abstract

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.

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