Evolution of pelvis types in basal dinosaurs
Zusammenfassung der Projektergebnisse
To investigate different pelvic shapes of archosaurs under a biomechanical viewpoint and identify shape-forming mechanical influences on the pelvis, Finite Element methods were applied to the pelvis of extant crocodylians. The data collection was accompanied by a first, static 2D FEA model of the crocodylian pelvis, which highlighted an important role of the abdominal muscle m. obliquus abdominis externus and showed effects of missing loads on the pubis and ilium. During the course of the first FEA and data collection, a scientific paper describing the anatomy of the infrapubic abdominal wall in Crocodylus was written. Because of the pioneering character of this work, it took a long time and several runs of the 3D FEA to identify all muscle forces that contribute during the chosen load cases to a force and moment equilibrium. Only the complete set of these muscle forces make is possible to get a uniform physiological distribution of compressive stresses in the 3D FEA, which then explains and confirms the investigated structure biologically and biomechanically. During the last phase of the project, some additional muscle forces have been discovered that still need to be added to the FE model to complete the analysis. However, the results of the first 3D FEA already give directions to the importance of individual muscles and explain bone shape and orientation in the crocodilian pelvis. The results show that the mobile pubis is actively braced in a tension chord by m. ischiopubis and m. ischiotruncus against cranially directed loads of the abdominal and ventilatory muscles, i.e. m. obliquus abdominis externus, m. diaphragmaticus and m. rectus abdominis. These muscles have an important role not only for moving the pubis during respiration, but also to reduce bending loads. The importance of m. obliquus abdominis externus as part of the abdominal musculature for stabilizing the trunk during terrestrial locomotion is shown. M. iliocostalis adds furthermore to lateral stabilization of the trunk and requires a large cranial process of the ilium as well as strong counteracting forces of m. ilioischiocaudalis to suspend the ilium. The ischium is suspended between rostrally directed respiratory muscles and caudally and dorsally directed locomotory muscles. Contribution of m. diaphragmaticus and m. rectus abdominis during activity of m. ilioischiocaudalis at least during aquatic locomotion make an active tension chord that prohibits a displacement of the ischium. The originally planned Finite Element Structure Synthesys of the crocodylian pelvis was omitted due to time reasons, but might be a topic for a future project. A FEA of a propubic dinosaur pelvis was not possible during the project time, but some first conclusions can be made from the FEA of the crocodile. In dinosaurs, the importance of abdominal muscles that have connection to the pubis and have an important role in stabilizing the lateral body wall during locomotion has also been underestimated. Changes in the attachment areas of the abdominal muscles are necessary prior to a re-orientation of the pubis in a caudal direction, but the absence of a hepatic-piston respiration mechanism in saurischian dinosaurs makes decoupling of the abdominal muscles from the pubis possible. Differences in the leg position between extant crocodylians and dinosaurs are indicative of differences in the position of single locomotory leg muscles, which influence morphology and position of pubis and ischium. Finally, the long bony tail of saurischian dinosaurs requires a strong m. ilioischiocaudalis for mobility and stabilization, which needs to be counteracted by rostrally directed muscles. This counter-play is an important reason why the ischium is never cranially directed. Reduction of the bony tail, however, makes a reduction of the ischium in dinosaurs possible.
Projektbezogene Publikationen (Auswahl)
- 2010. Pelvis shape and functional morphology of the pelvic girdle in extant crocodiles and dinosaurs. p. 74, 8th Meeting of the European Association of Vertebrate Palaeontologists, Aix-en-Provence, June 7th-12th, Abstract volume
Schwarz-Wings, D., Fechner, R. & Witzel, U.
- 2011. A functional explanation of the propubic and opisthopubic pelvis in extant archosaurs and dinosaurs, p. 107, Annual Meeting of the Society of Vertebrate Paleontology, Las Vegas, USA, Supplement to the online Journal of Vertebrate Paleontology, November 2011
Fechner, R. & Schwarz-Wings, D.
- 2011. The pelvis architecture of extant archosaurs and dinosaurs: a functional explanation. p. 44, IV Congreso Latinoamericano de Paleontolgía de Vertebrados, San Juan, Argentina
Fechner, R. & Schwarz-Wings, D.
- (2013). The muscles of the infrapubic abdominal wall of a six month-old Crocodylus niloticus (Crocodylia: Reptilia). - Anat Histol Embryol, 42 (3): 175-182
Fechner, R. & Schwarz-Wings, D.
- 2013. Finite Element Methods as a means for the mechanical analysis of the crocodilian pelvis. p. 46. In Reitner, J., Qun, Y., Yongdong, W., Reich, M. (Eds.) Palaeobiology and Geobiology of Fossil Lagerstätten through Earth History. Abstract Volume. Universitätsverlag Göttingen
Fechner, R. & Schwarz-Wings, D.
