Extreme postcranial pneumaticity in derived sauropod dinosaurs from the Upper Cretaceous of Argentina

IGNACIO A. CERDA; LEONARDO SALGADO; JAIME POWELL

Jornada; XXVI Jornadas Argentinas de Paleontología de Vertebrados; 2012

Birds are the only extant group of vertebrates that possesses a pneumatic postcranial skeleton, which results from invasion of bone by extensions (diverticula) from the lung and air-sac system. The osteological correlates of these avian airsac diverticula have been characterized, and postcranial skeletal pneumaticity (PSP) has been reported in numerous extinct archosaurs including pterosaurs and non-avian theropods. In sauropod dinosaurs, the pattern of PSP in the axial skeleton has been interpreted as evidence for an avian-like air sac system in this group. Here we report a case of extreme PSP in a group of small-bodied, armored titanosaurian sauropods from the Upper Cretaceous of South America. Based on osteological data, we corroborate pneumatic features in the pelvic girdle of this group of sauropod dinosaurs and report an extensive invasion of pneumatic diverticula along the vertebral column, reaching the distal portion of the tail. Also, we provide the first evidence of pneumaticity in the scapular girdle for a sauropodomorph dinosaur. The strict correlation between specific air sacs and the axial elements that they pneumatize in extant birds allow to infer the presence of an avian-like clavicular air sac in sauropod dinosaurs. Our study also reveals that the extreme PSP in archosaurs is not restricted to pterosaurs and theropod dinosaurs. The PSP appears to be related to the development of a heterogeneous respiratory system, which possibly allowed a more efficient, flow-through ventilation of the pulmonary apparatus.