1997/11/14 by John A. Ruben, Terry D. Jones, Nicholas R. Geist +1 · 4 citations
Environmental Science · Earth and Planetary Sciences · #Physiological and biochemical adaptations #Evolution and Paleontology Studies #Paleontology and Evolutionary Biology
paper · doi:10.1126/science.278.5341.1267
openalex publication_date 1997/11/14 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
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.