A monodactyl nonavian dinosaur and the complex evolution of the alvarezsauroid hand

Digital reduction is a striking evolutionary phenomenon that is clearly exemplified in theropod dinosaurs by the functionally didactyl manus of tyrannosaurids, the flight-adapted manus of birds (Aves), and the tridactyl but digit II-dominated manus of alvarezsauroids. The enlargement of manual digit II in alvarezsauroids and the concurrent reduction of the lateral digits have been interpreted as adaptations for digging, although no detailed...