Key words: Ornithischia, Pachycephalosauria, Marginocephalia, Stenopelix, Cretaceous, Germany.

Richard J. Butler [R.Butler@nhm.ac.uk], Department of Palaeontology, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK; and Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK (corresponding author); Robert M. Sullivan [rsullivan@state.pa.us], Section of Paleontology and Geology, The State Museum of Pennsylvania, 300 North Street, Harrisburg, PA 17120-0024, USA