- The Paleontological Society
Theoretical models of skeletal structures provide suitable frameworks to assess macroevolutionary patterns of form change. We discuss three theoretical approaches to account for morphological patterns of the pelvic girdle in archosaurs. Every approach targets a different level of organization within the concept of morphospace. First, we build a morphocline by applying a mathematical transformation to the outline of the hip of the theropod dinosaur Deinonychus antirrhopus, in order to look at theoretical paths of evolutionary change based on changes of proportion. Second, we analyze the variability of a sample of 86 hips within a theoretical construction that incorporates information about the spatial orientation of the three paired bones that build this skeletal compound. Finally, we look at boundary patterns within these hips as a basis for generating a formalism based on graph theory. Insights about the evolution and development of the archosaur triradiate pelvis and its morphological trends are suggested in the light of each theoretical approach, with a special focus on the convergent evolution of a retroverted pubis in ornithischians and birds.