cranial ontogeny in stegoceras validum (dinosauria pachycephalosauria) a quantitative model of pachycephalosaur dome growth and variation剑角龙validum颅个体发生(恐龙pachycephalosauria)肿头龙圆顶增长和变化的定量模型.pdf

Cranial Ontogeny in Stegoceras validum (Dinosauria: Pachycephalosauria): A Quantitative Model of Pachycephalosaur Dome Growth and Variation 1 1,2 3 4 1 Ryan K. Schott *, David C. Evans , Mark B. Goodwin , John R. Horner , Caleb Marshall Brown , Nicholas R. Longrich5 1 Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada, 2 Royal Ontario Museum, Toronto, Ontario, Canada, 3 Museum of Paleontology, University of California, Berkeley, California, United States of America, 4 Museum of the Rockies, Montana State University, Bozeman, Montana, United States of America, 5 Department of Geology, Yale University, New Haven, Connecticut, United States of America Abstract Historically, studies of pachycephalosaurs have recognized plesiomorphically flat-headed taxa and apomorphically domed taxa. More recently, it has been suggested that the expression of the frontoparietal dome is ontogenetic and derived from a flat-headed juvenile morphology. However, strong evidence to support this hypothesis has been lacking. Here we test this hypothesis in a large, stratigraphically constrained sample of specimens assigned to Stegoceras validum, the best known pachycephalosaur, using multiple independent lines of evidence including conserved morphology of ornamentation, landmark-based allometric analyses of frontoparietal shape, and cranial bone histology. New specimens show that the diagnostic ornamentation of the parietosquamosal bar is conserved throughout the size range of the sample, which links flat-headed specimens to domed S. validum. High-resolution CT scans of three frontoparietals reveal that vascularity decreases with size and document a patter