Sternal Ribs

Another characteristic shared by pterosaurs and birds:
http://www.ploscollections.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0004497;jsessionid=A1CA60013B42AE8DCA4EDCACEF3A2BF7
The morphology of the trunk of pterosaurs differs from previous descriptions in several aspects that are crucial to lung ventilation and respiratory efficiency. Contrary to earlier reports [1], [7], [29], [30], pterosaur sternal ribs are not of uniform length and posterior elements commonly exhibit a two-fold or greater increase in length (Figs. 2, S1; Table S2). Consequently, and unlike recent reconstructions of pterosaurs which tend to show a horizontal or even posterodorsally sloping sternum, the posterior margin of the pterosaur sternum sloped posteroventrally, similar to birds[21]. (Leon P. A. M. Claessens^1*, Patrick M. O'Connor², David M. Unwin³⁾