Gas exchange potential in reptilian lungs: implications for the dinosaur-avian connection

The theory that birds evolved from a group of small terrestrial theropod di nosaurs has created much controversy. One argument proposed against this th eory is that the lungs of early theropods were incapable of sustaining endo thermic gas exchange requirements and could not have given rise to the lung s of birds. A reexamination of the comparative physiological and morphologi cal literature combined with a theoretical analysis of gas exchange potenti al indicates that non-avian lungs would not constrain the gas exchange requ irements of early endotherms. Furthermore, our analysis suggests that facto rs besides diffusive gas exchange were important in the evolution of the di stinct morphology of the highly effective avian and mammalian lungs. (C) 19 99 Elsevier Science B.V. All rights reserved.