New data on pachycephalosaurid dinosaurs (Reptilia: Ornithischia) from North America

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Abstract
Several new significant specimens of pachycephalosaurid dinosaurs from Upper Cretaceous strata of Canada and the USA are described and figured. The domes of an unusual pachycephalosaurid from the Judith River Formation (Campanian) of Alberta show a slightly thickened frontal with an ornamentation of bony tubercles; they are referred to a new genus [ORNATOTHOLUS (type species: Stegoceras browni Wail and Galton, 1979)]. A new genus [STYGIMOLOCH (type species: S. spinifer sp. nov.)] of Pachycephalosauridae is described from the Hell Creek Formation (Maastrichtian) of Montana; it has horn-like projections on the squamosal. Sutural fusion between the quadrate and squamosal of Pachycephalosaurus is reported; this is an unusual condition among the Ornithischia. The biological significance of certain cranial features is considered. [Other taxa described include Stegoceras sp. and P. wyomingensis (Gilmore, 1931).].