Bony morphology of feather attachment and composition of wing shape. (a) – (c) Major bony landmarks as visible on a rock pigeon (Columba livia). (a) Dorsal view of the distal forelimb. I: digit I; II-1: proximal phalanx digit II; II-2: distal phalanx digit II; III: digit III; IIP: internal index process; cmc: carpometacarpus; r: radius; u: ulna. (b) 1° attachment features on digits II-III, dorsal view. dpf: dorsal phalangeal fossae (primaries VIII-IX); fp: flexor process of digit III (primaries I-VI); iip1: internal index process (primaries IX-X); iip2: position of caudal lobe of internal index process (primary IX); tvi: tendon of ventral interosseous muscle; tfdm: tendon of flexor digiti minimi muscle. (c) 2° attachments on the ulna, caudal view. drp: dorsal remigial papillae; crp: caudal remigial papillae. (d) Schematic of flight feather attachment and contribution to wing shape in a pink-footed shearwater Puffinus creatopus (left) and a roadrunner Geococcyx californianus (right), taxa with roughly equivalent wing area but very different wing shapes and functions. Shading indicates groups of feathers with distinct attachment points. Note that distal primaries form the pointed wingtip in Puffinus, while the rounded wingtip in Geococcyx is formed by more proximal primaries. pd1°: predigital primary (II-2); md1°: middigital primaries (II-1); ad1°: addigital primary (III); cm1°: carpometacarpal primaries (III + carpometacarpus + tfdm); 2°: secondaries. Bird images: Puffinus courtesy M. Taylor (CC-by-SA 3.0) 2009; Geococcyx courtesy G. Kramer and USFWS, 2009.