Pneumatic structures in the cervical vertebrae of the Late Jurassic Tendaguru sauropods Brachiosaurus brancai and Dicraeosaurus

Abstract

The presacral vertebrae of sauropod dinosaurs were surrounded and invaded by a complex system of pneumatic diverticula, which originated most probably from cervical air sacs connected with the respiratory apparatus. Cervical vertebrae of Brachiosaurus brancai and Dicraeosaurus sp., two sauropods from the Late Jurassic (?Oxfordian-Kimmerigian-Tithonian) eastern African locality Tendaguru, were examined with computed tomography to visualize internal pneumatic structures. With this method, comparative reconstructions of pneumatic diverticula in the neck of these sauropods were done that help to understand the biomechanical role of vertebral pneumaticity in sauropods. Internal pneumatic structures in Brachiosaurus brancai are semicamellate with few large camerae in the vertebral centrum, surrounded by pneumatic camellae. Dicraeosaurus exhibits a procamerate pneumatization pattern with few deep fossae penetrating to a broad median strut in the vertebra, but no internal pneumaticity was found. The semicamellate pneumatization pattern of Brachiosaurus brancai corresponds with another Late Jurassic Brachiosaurus specimen, whereas in Cretaceous brachiosaurid taxa like Sauroposeidon, the complexity of internal pneumatization increases to form a fully camellate pneumatization pattern. In Dicraeosaurus, internal pneumatization has most likely secondarily been reduced. Brachiosaurus and Dicraeosaurus possess a similar distribution of main external pneumatic diverticula, with Brachiosaurus having much more subdivided diverticula. Due to the weight reduction achieved by these pneumatic diverticula, the neck of Brachiosaurus was up to 25 per cent lighter than without pneumatic structures, whereas that of Dicraeosaurus was only 6 per cent lighter. Pneumatization of the cervical vertebrae therefore can play an important role in lightening some sauropods.