FIG. 1 in Pennaraptoran Theropod Dinosaurs Past Progress And New Frontiers

FIG. 1. Flight feather morphology across paravian phylogeny (modified from Feo et al., 2015). Early-diverging taxa (indicated by dashed pink lines) exhibit flight feather trailing edges characterized by narrow angles of barb-to-rachis attachment. The crownlike condition (broad angles of barb-to-rachis trailing edge attachment; blue dashed lines) arose on the internode subtending Ornithothoraces, and may have conferred a more flexible trailing edge of the wing during flight in order to increase feather-to-feather contact and maintenance of a coherent wing surface in flight during active downstrokes. Silhouettes from phylopic.org.