Evidence for bird‐like air sacs in saurischian dinosaurs

Abstract

Among extant tetrapods, pneumatic postcranial bones are only present in birds, and they are osteological correlates of the diverticular lungs and pulmonary air sacs. The presence of postcranial pneumaticity in sauropod and theropod dinosaurs suggests that some form of air sac system was also present in the dinosaurian ancestors of birds. In particular, anatomical and evolutionary patterns of pneumatization in nonavian saurischian dinosaurs are diagnostic for specific air sacs, including the cervical, clavicular, and abdominal air sacs. Pneumatic hiatuses are gaps in the pneumatization of the vertebral column and indicate pneumatization from multiple sources. A pneumatic hiatus in Haplocanthosaurus provides additional support for the presence of abdominal air sacs in sauropods. The origins of postcranial pneumaticity in archosaurs are enigmatic because the earliest putative traces of pneumaticity are difficult to distinguish from skeletal imprints of other soft tissues. Nevertheless, several lines of evidence suggest that air sac-driven lung ventilation was primitive for Saurischia.

A new sauropod dinosaur from the Early Cretaceous of Tunisia with extreme avian-like pneumatization

“…The holotype of T. hannibalis is interpreted to represent an ontogenetically mature individual based on the combination of large size, co-ossification of the sacrum, obliterated neurocentral suture in caudal vertebrae (Fig. 2b), and extensive pneumatization of the pelvic and caudal region 18 .…”

“…ARTICLE surface of the ischium of Tataouinea does not differ in shape, depth and presence of clearly defined margins, from the pleurocoels in the axial skeleton and is interpreted as pneumatic in origin. Pneumatic invasion of the pelvic girdle has been reported in both theropods and neosauropods 18,26,28 , but all previous reports were limited to the ilium. Other sauropods show small internal chambers pneumatising the iliac blades but not invading the pubic peduncle 26 , whereas a large chamber hollowing the latter peduncle was reported only in theropods 28 .…”

“…In the pelvis, pneumatization of the iliac blades, bones adjacent to the axial skeleton, preceded the pneumatization of the pubic peduncle of ilium and the ischium, bones not in direct vertebral contact, following a 'proximal-first patter'. Large pneumatopores penetrating the caudosacral vertebrae were considered as indication of abdominal air sacs 29,30 , a necessary component of the avian-like lung ventilation system 18 . A more conservative approach 28 considered axial pneumatization as ambiguous evidence of abdominal air sacs, and only pelvic pneumatization in areas removed from contact with the sacrum as unambiguous evidence of abdominal air sacs, to avoid potential confusion with extramural pneumatization by posterior expansions of the cervical air sacs.…”

“…The spinal foramen shows clearly defined margins and is present symmetrically in both sides of the lateral surface, leading to the corresponding camerate sector of the semicamellate NATURE COMMUNICATIONS | DOI: 10.1038/ncomms3080 ARTICLE structure. A semilunate fossa is present ventral to the left foramen; it likely represents incipient pneumatization 18 . The first five caudal vertebrae were preserved in their anatomical series (Fig.…”

Balance and Strength—Estimating the Maximum Prey‐Lifting Potential of the Large Predatory Dinosaur Carcharodontosaurus saharicus

“…The use of birds for lung volume estimation is based on the high degree of pneumatization seen in the skeletons of sauropods and both extinct and extant theropods (birds), and the inference that all these animals shared a bird-like, flow-through lung, and system of air sacs (Wedel, 2009). Table 1 summarizes the models of C. saharicus and L. tessonei.…”