Cross-sections of the wing of A. santanae. (a) Three-dimensional reconstruction of the fleshed-out wing skeleton, cheiropatagium, cruropatagium, and the narrow and broad reconstructions of the propatagium, indicating the plane of the cross-section used for the wind tunnel models. (b–d) Wing sections, with (b) broad, (c) narrow and (d) no propatagium. All three sections are shown at an angle of attack of 0°. Scale bar=50 mm. Abbreviations and symbols: bp, broad propatagium; np, narrow propatagium; s, spar; θ_e, entry angle; θ_pd, propatagium deflection angle.

Skeletal reconstruction of A. santanae. (a) Reconstructed skeleton of the right wing and membrane outlines in dorsal view, adapted from Wellnhofer (1991b), showing the pteroid in the antero-ventral orientation, supporting a broad propatagium (solid line) and in the medial orientation, supporting a narrow propatagium (broken line): scale bar=200 mm. (b) Right medial carpal in distal view and right pteroid in proximal view, showing the articular surfaces of the carpal–pteroid joint: scale bar=20 mm. (c) Right wrist in antero-medial view, showing articular motion of the pteroid. Two planes have been superimposed, intersecting at the carpal–pteroid joint—one parallel to the wing spar, one normal to it. During the initial phase of flexion the pteroid (solid line) occupies the normal plane, and angulation thus takes the form of pure depression. During the second phase the articular head of the pteroid rotates laterally with respect to the medial carpal, and angulation therefore gradually shifts from depression to adduction. The pteroid swings out of the normal plane until at the limit of flexion (broken line) it comes to occupy the parallel plane. Abbreviations: ch, cheiropatagium; cr, cruropatagium; ds, distal syncarpal; f, femur; fov, fovea of the medial carpal; h, humerus; lf, lateral facet of the pteroid; mc, medial carpal; mf, medial facet of the pteroid; pro, propatagium; ps, proximal syncarpal; pt, pteroid; r, radius; t, tibiotarsus; u, ulna; wf, wing-finger; wm, wing-metacarpal.

Wind tunnel results for the pterosaur wing sections. (a) Polar diagram, in which the lift and profile drag forces measured for each model have been converted into their respective dimensionless coefficients, C_L and C_D,pro (equations (4.1) and (4.2)), and plotted against each other. Each point represents a C_L and C_D,pro value measured at a single angle of attack, and angle of attack increases from −2° at the bottom left to 20° at the top right. Open circles, broad forewing model; closed circles, narrow forewing model; triangles, model without a forewing. (b) L : D ratios. Symbols as in (a). (c) Polar diagram showing the effects of variation in θ_pd on the performance of the broad propatagium model. Open squares, θ_pd=30°; closed squares, θ_pd=40°; crosses, θ_pd=50°. The solid line indicates the best performance over the entire angle of attack range, and it is this composite polar for the broad propatagium model that has been plotted in (a). (d–f) Polar diagram showing the effects of variation in ϵ on the performance of (d) the broad propatagium model, (e) the narrow propatagium model and (f) the model without a propatagium. Open diamonds, ϵ=0.02; closed diamonds, ϵ=0.04; open triangles, ϵ=0.06. The solid lines again indicate the best performance, and are plotted in (a).