Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa; Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, United States
Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa; European Synchrotron Radiation Facility, Grenoble, France; Natural History Museum, Imaging and Analysis Centre, London, United Kingdom
Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa; School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
Department of Biological Sciences, University of Alberta, Edmonton, Canada
William J de Klerk
Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa; Department of Earth Sciences, Albany Museum, Grahamstown, South Africa
Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa; Division of Paleontology, American Museum of Natural History, New York, United States
Ornithischian dinosaurs were ecologically prominent herbivores of the Mesozoic Era that achieved a global distribution by the onset of the Cretaceous. The ornithischian body plan is aberrant relative to other ornithodiran clades, and crucial details of their early evolution remain obscure. We present a new, fully articulated skeleton of the early branching ornithischian Heterodontosaurus tucki. Phase-contrast enhanced synchrotron data of this new specimen reveal a suite of novel postcranial features unknown in any other ornithischian, with implications for the early evolution of the group. These features include a large, anteriorly projecting sternum; bizarre, paddle-shaped sternal ribs; and a full gastral basket – the first recovered in Ornithischia. These unusual anatomical traits provide key information on the evolution of the ornithischian body plan and suggest functional shifts in the ventilatory apparatus occurred close to the base of the clade. We complement these anatomical data with a quantitative analysis of ornithischian pelvic architecture, which allows us to make a specific, stepwise hypothesis for their ventilatory evolution.
