There can be little doubt that pterosaurs had an excellent repiratory system and expansion of the ribcage facilitated this. This was a good paper in many respects and covered several important issues. However...

Claessens et al. (2009, fig. 3a) sought to demonstrate ventral expansion of the pterosaur abdomen to facilitate respiration via “caudoventral rotation of the prepubis.” In the Rhamphorhynchus specimen (MB-R. 3633.1-2) Claessens et al. (2009, fig. 2a-c) used as an example, they considered the prepubis to be articulated to the pubis with a movable joint and with its major axis in line with the gastralia. The prepubis was correctly identified, but Claessens et al. (2009) failed to notice it had been rotated during taphonomy such that the hollow cylindrical stem moved into the plane of the gastralia with its pubic articulation open anteriorly. The actual anterior process of the distal prepubis remains clearly visible ventral to the pubis (Claessens et al. 2009, fig. 2a-c). The ventral prepubis continues largely hidden beneath the pelvis. Properly rotated and configured like that of other pterosaurs (see later), the prepubis actually deepens the torso. In Rhamphorhynchus muensteri the torso would have been greatly deepened if the unusually elongated prepubis were correctly configured, extending ventrally. In such a configuration the proposed (Claessens et al., 2009) “caudoventral rotation at the pubis-prepubis joint” could only stretch the gastralia away from the sternal complex, not ventrally expand the torso. Perhaps more importantly, the actual pubis-prepubis joint is flat or slightly expanded preventing caudoventral rotation. To that point, in Claessens et al. (2009, fig. 3b) the prepubis of Pteranodon is correctly figured extending ventrally from the pubis and their own figure demonstrates torso expansion during respiration without prepubis rotation. Claessens et al. (2009, fig. 3c) introduce a hypothetical prepubis in Anhanguera aligned with the gastralia. The prepubis has not been found in that specimen (AMNH 22555) and is unknown in other published anhanguerids.

In summary, ventral expansion of the torso would have facilitated respiration. However, as the prepubis was already oriented chiefly ventrally, no expansion could have been expected from its movement, which was prevented in any case by a flat-to-flat pubis-prepubis joint in all pterosaurs.