Hingabe an das morphologische Extrem - Systematische Revision des sauropoden Dinosauriers Dicraeosaurus aus dem Oberen Jura von Tendaguru (Tansania) und Rekonstruktion der dreidimensionalen Beweglichkeit und Biomechanik des Halses und Schultergürtels der Dicraeosauridae
Zusammenfassung der Projektergebnisse
The study presented here is centered around the small and rather short-necked sauropod Dicraeosaurus from the Late Jurassic Tendaguru Formation of southeastern Tanzania. Two temporally distinct species of Dicraeosaurus, D. hansemanni and D. sattleri, are known from the Tendaguru area, and both were ostelogically described in new detail in this work. The osteological description of the cranial, mandibular and postcranial material of both species allowed us to define autapomorphies for each of them, confirming their taxonomic validity. Isolated material attributed only to Dicraeosaurus sp. in the Tendaguru-collection of the MfN could be assigned to one of the two species. It was also possible to code both species separately for a new phylogenetic analysis, as well as to provide a generic diagnosis for the taxon Dicraeosaurus. A new osteological reconstruction of the skull including its orientation with respect to the cervical vertebral column, was devised, including studies of the endocast of Dicraeosaurus. The skull endocast displays remarkably extended dorsal excrescence and olfactory bulbs, both features contrasting the conditions in other sauropods. The triangular semicircular canals of Dicraeosaurus are also remarkable, all in all inducing a rostroventrally directed rostral skull portion, with both the eyes and the lateral semicircular canal positioned horizontally. Phylogenetically, with the hitherto uncertain validity of the two species, Dicraeosaurus has been mostly coded and studied on the genus level. In this study we were able to code both species separately, which bears some importance as all other dicraeosaurid taxa are monospecific. Thus, the more detailed character matrices and analysis of both species helped to refine the studies of the systematic relationships of dicraeosaurids, confirming also other studies. The new phylogenies confirm also studies of the biogeography and migration of dicraeosaurids. All well preserved material was 3D scanned. The complete skeleton of Dicraeosaurus hansemanni was assembled as a 3D model that helps to reconstruct the mobility of the neck of Dicraeosaurus as well as its muscular support by the shoulder girdle. The neck mobility of Dicraeosaurus exceeds previous models in terms of its range of motion in dorsal direction. It was demonstrated that the combination of high neural spines in the neck, bulky and badly pneumatized cervical vertebrae and a robust skull provided specific requirements to the neck support by cervicodorsal muscles and ligaments, and also the suspension on the shoulder girdle, and can be related to reduced neck lengths in Dicraeosaurus and other dicraeosaurids. The wide distribution of dicraeosaurid taxa in Laurasia and Gondwana demonstrates the adaptability of these sauropods to ecosystems with a complex and variable fauna of herbivorous dinosaurs, and the “competitiveness” of the special functional complex of neck and shoulder girdle.
