Hanssuesia sternbergi (Brown & Schlaikjer, 1943)

Hanssuesia sternbergi

Colepiocephale lambei Stegoceras validum Stegoceras novomexicanum Goyocephale lattimorei Homalocephale calathocercos Tylocephale gilmorei Foraminacephale brevis Amtocephale gobienses Prenocephale prenes Acrotholus audeti Pachycephalosaurus wyomingensis Alaskacephale gongloffi Dracorex hogwartsia Stygimoloch spinifer Sphaerotholus goodwini Sphaerotholus buchholtzae increased from 117 to 663 and the resolution of the strict consensus tree dropped considerably, collapsing Homalocephale , Tylocephale , Foraminacephale , Amtocephale , Prenocephale , and Acrotholus into a polytomy with the Sphaerotholus – Pachycephalosaurus clade ( Fig. 28 View Figure 28 , left). When F. brevis was removed completely the number of MPTs increased further to 4065, and in the strict consensus tree the Sphaerotholus – Pachycephalosaurus clade was collapsed into a complete polytomy and Goyocephale and Homalocephale were also collapsed into a polytomy ( Fig. 28 View Figure 28 , right). These results clearly indicate that inclusion of F. brevis as a distinct species is important for resolution of pachycephalosaur systematics, and that the material referred here contains important phylogenetic information. It is also likely that the lack of similar material from other species is hindering our ability to properly resolve pachycephalosaur phylogenetic relationships.