New data on the postcranial skeleton of the tapejarid Sinopterus from the Early Cretaceous Jehol Biota

We reported a new skeleton of the tapejarid Sinopterus from the Jehol Biota, providing more additional information of the postcranial morphology, especially the anatomy of the tail, the pectoral and the pelvic girdles. The reduced tail is composed of nine caudal vertebrae, as a new evidence of the tail reduction of the azhdarchoids. An eminence is present on the posterior surface above the coracoidal crest, as the first record in the Jehol tapejarids, comparable with the modest coracoidal tubercle of the Brazilian tapejarids Caiuajara, Keresdrakon, and Tupandactylus, which implies a coexistence of the coracoidal crest and the coracoidal tubercle in the tapejarids. The pelvic girdle has an elongate pre-acetabular process, a hatchet-like postacetabular process, a medium-sized obturator foramen, and a kidney-shaped prepubic blade. The postacetabular process is unconstricted in the mid-shaft, and its terminus is subequal to the acetabulum in length, distinct from the more derived condition in the Brazilian tapejarids. This discovery sheds a new light on the evolution of the postcranial morphology in tapejarids and azhdarchoids.