the dome were less angled than in Stegoceras. Discovery and naming The holotype of Foraminacephale is CMN 1423, a nearly complete frontoparietal dome collected in Dinosaur Provincial Park, Alberta in 1902 and reported on during the same year. The layers of rock where the specimen were found belong to the Dinosaur Park Formation of the Belly River Group. Various other fragments of the skull are also known from the Dinosaur Park Formation, representing juvenile, subadult, and adult individuals. Although it has been reported that many specimens are known from the contemporary Oldman Formation, only one (catalogued as TMP 2015.044.0041) can definitely be assigned to Foraminacephale. Another specimen from the Horseshoe Canyon Formation formerly assigned to Foraminacephale, CMN 11316, was re-identified as a small, juvenile indeterminate pachycephalosaurine. CMN 1423 was first assigned to a new species of Stegoceras by Lawrence Lambe in 1918; there was considerable debate over whether "S." brevis represented a truly distinct animal or simply a morph, perhaps the female, of S. validum. Later, it was assigned to Prenocephale by Robert M. Sullivan in 2000, and then it was assigned to Sphaerotholus by Longrich, Sankey & Tanke in 2010. In 2011, Ryan Schott suggested a new generic name, Foraminacephale, in his Master of Science thesis, resulting in a new combination Foraminacephale brevis. It remained an invalid nomen ex dissertatione until Schott and David Evans formally renamed "S." brevis to Foraminacephale brevis in 2016. The generic name combines Latin foramina ("foramina") with cephale, Latinised Greek for "head", referring to the many pits that covered the top of its dome. Classification A phylogenetic analysis in 2016 found that Foraminacephale was a member of the Pachycephalosaurinae, in a more derived position than Stegoceras, but in a more basal position than Prenocephale. The consensus of the phylogenetic trees recovered is shown below. The topology of this phylogenetic tree is not very stable, likely due to the incompleteness of most pachycephalosaur specimens. Paleoecology The Belly River Group is particularly rich in pachycephalosaur remains; 70% of all known pachycephalosaur fossils come from this region. Because of a lack of understanding of pachycephalosaur ontogeny, various authors have assigned this material to anywhere from a single species, Stegoceras validum, to four different genera. This has significant implications for the Late Cretaceous biodiversity of herbivorous dinosaurs. The 2016 description of Foraminacephale recognized four distinct species of pachycephalosaur from the Belly River Group: Stegoceras, Foraminacephale, Hanssuesia, and Colepiocephale,