Heterochrony structured theropod wing for flight and influenced its evolutionary paths

<p>The theropod forewing evolution could have been shaped by changes in developmental timing, as seen for the skull. Theropods leading to birds suffered miniaturization with forelimb lengthening attributed to heterochrony (changes in developmental timing and/or rate) which has never been strictly tested. Using phylogenetic analysis of growth series shape-change, we detected paramorphism in the paravian node as an immature wing resembling adult early-diverging theropods. The coinciding development of pennaceous feathers, longer wings, and mobile shoulders in the paravian common ancestor demonstrates a major reorganization of the forelimb just before flight appeared. Once flight evolved, heterochrony continued influencing wing evolution and the rapid early diversification of avian flight styles. Our study extends the role of heterochrony to the wings of theropods, playing a central role in flight evolution.</p>