As the earliest birds known, the late Jurassic specimens of Archaeopteryx have been the object of great speculative interest. Ostrom1-3 has argued that Archaeopteryx was a terrestrial, cursorial predator that represents a preflight stage in the origin of birds in which the forelimbs were used as nets to trap insects. So far, this has been challenged mainly on the grounds that such activity would have caused excessive feather wear4. The principal evidence for regarding Archaeopteryx as flightless, or at best an inept non-flapping glider, has come from interpretations of the structure of the pectoral girdle. The absence of an ossified sternum for attachment of flight muscles has long been cited. More recently, it has been argued that the structure of the coracoid of Archaeopteryx would not have permitted the supracoracoideus muscle to function as a wing elevator2,5. Because the asymmetrical remiges of Archaeopteryx prove that the wing had an aerodynamic function6, we now hope to show that neither of the preceding points precludes a capacity for powered flight in Archaeopteryx.