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Science 14 November 1997:
Vol. 278. no. 5341, pp. 1267 - 1270
DOI: 10.1126/science.278.5341.1267
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Reports

Lung Structure and Ventilation in Theropod Dinosaurs and Early Birds

John A. Ruben, Terry D. Jones, * Nicholas R. Geist, W. Jaap Hillenius

Reptiles and birds possess septate lungs rather than the alveolar-style lungs of mammals. The morphology of the unmodified, bellowslike septate lung restricts the maximum rates of respiratory gas exchange. Among taxa possessing septate lungs, only the modified avian flow-through lung is capable of the oxygen-carbon dioxide exchange rates that are typical of active endotherms. Paleontological and neontological evidence indicates that theropod dinosaurs possessed unmodified, bellowslike septate lungs that were ventilated with a crocodilelike hepatic-piston diaphragm. The earliest birds (Archaeopteryx and enantiornithines) also possessed unmodified septate lungs but lacked a hepatic-piston diaphragm mechanism. These data are consistent with an ectothermic status for theropod dinosaurs and early birds.

J. A. Ruben, T. D. Jones, N. R. Geist, Department of Zoology, Oregon State University, Corvallis, OR 97331-2914, USA.
W. J. Hillenius, Department of Biology, College of Charleston, Charleston, SC 29424, USA.
*   To whom correspondence should be addressed. E-mail: jonest{at}bcc.orst.edu

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