Several aspects of the pelvic girdle suggest that pterosaurs were specialized for pelvic aspiration during flight. As in birds, the three pelvic bones of pterosaurs were solidly fused into a single unit (Fig. 9), and an increased number of dorsal vertebrae were incorporated into the sacrum (3 to 5 in Rhamphorhynchus and as many as 10 in Pteranodon) (Wellnhofer, 1978, 1987). The preacetabular process of the ilium was very long and in pterodactyloids it was fused with additional dorsal vertebrae to form a synsacrum-like structure (Eaton, 1910). The distal ends of the pubic bones did not meet on the ventral midline, but the ischiadic portion of the puboischiadic plate was fused at the midline (Padian, 1983); making the pelvis partially open ventrally. (
David R. Carrier2,1,2and Colleen G. Farmer1,2)
At their distal ends, the pubic bones expand laterally and medially into broad plates that form the ventral margin of the posterior belly.