Cranium of Sphaerotholus buchholtzae in dorsal view (arrows indicate lesions), from Peterson et al. (2013).

Belongs within: Genasauria.

The Pachycephalosauria are a group of bipedal herbivorous dinosaurs with a thickened skull roof known from the Cretaceous of Eurasia and North America (Maryanska et al. 2004).

Characters (from Maryanska et al. 2004): Skull roof thickened; frontal excluded from orbital margin; postorbital bar with dorsal surface flat, broad; parietal without caudolateral wings; squamosal extended onto occiput, bearing tubercles on caudolateral margin; basal tubera thin, platelike; prootic-basisphenoid plate contacting pterygoid-prootic plate; jugal and quadrate eliminating free ventral margin of quadratojugal; dorsal vertebrae with double ridge-and-groove articulations; sacral ribs elongate; caudal basket of fusiform ossified tendons present; illium with sigmoidal border; medial process present on iliac blade; pubis nearly excluded from acetabulum.

    |  i. s.: Yaverlandia Galton 1971 MCW04
    |           `--Y. bitholus Galton 1971 MCW04
    |         Heishansaurus Bohlin 1953 MCW04, D07
    |           `--H. pachycephalus Bohlin 1953 (n. d.) MCW04
    |--Stenopelix Mayer 1857 MCW04
    |    `--S. valdensis Meyer 1857 MCW04
    `--+--Wannanosaurus Hou 1977 MCW04
       |    `--W. yansiensis Hou 1977 MCW04
       `--Goyocephala MCW04
            |--Goyocephale Perle, Maryańska & Osmólska 1982 MCW04
            |    `--G. lattimorei Perle et al. 1982 MCW04
            `--Homalocephaloidea MCW04
                |--Homalocephale Maryańska & Osmólska 1974 MCW04
                |    `--H. calathocercos Maryańska & Osmólska 1974 MCW04
                `--+--Ornatotholus Galton & Sues 1983 MCW04
                   |    `--*O. browni (Wall & Galton 1979) S03 [=Stegoceras browni MCW04]
                   `--Pachycephalosauridae [Pachycephalosaurinae, Pachycephalosaurini, Tholocephalidae] MCW04
                        |  i. s.: ‘Troodon’ bexelli Bohlin 1953 MCW04 [=Stegoceras bexelli S03]
                        |         Gravitholus Wall & Galton 1979 MCW04
                        |           `--*G. albertae Wall & Galton 1979 (n. d.) S03
                        |         Dracorex hogwartsia D07
                        |--Stygimoloch Galton & Sues 1983 [incl. Stenotholus Giffin, Gabriel & Johnson 1987] MCW04
                        |    `--*S. spinifer Galton & Sues 1983 S03 (see below for synonymy)
                        `--+--Stegoceras Lambe 1902 [incl. Colepiocephale Sullivan 2003, Hanssuesia Sullivan 2003] MCW04
                           |    |--*S. validum Lambe 1918 S03, MCW04 (see below for synonymy)
                           |    `--S. edmontonense (Brown & Schlaikjer 1943) MCW04 (see below for synonymy)
                           `--+--Pachycephalosaurus Brown & Schlaikjer 1943 (see below for synonymy) MCW04
                              |    `--*P. wyomingensis (Gilmore 1931) S03 (see below for synonymy)
                              `--+--Tylocephale Maryańska & Osmólska 1974 MCW04
                                 |    |--T. bexelli D07
                                 |    `--T. gilmorei Maryańska & Osmólska 1974 S03
                                 |--Prenocephale Maryańska & Osmólska 1974 S03
                                 |    `--*P. prenes Maryańska & Osmólska 1974 S03
                                 `--Sphaerotholus Williamson & Carr 2002 MCW04
                                      |--S. buchholtzae Williamson & Carr 2002 MCW04
                                      |--S. edmontonense D07
                                      `--S. goodwini Williamson & Carr 2002 MCW04 [=Prenocephale goodwini S03]

Pachycephalosaurus Brown & Schlaikjer 1943 (nom. cons.) [incl. Tylosteus Leidy 1872] MCW04

*Pachycephalosaurus wyomingensis (Gilmore 1931) S03 [=Troodon wyomingensis MCW04; incl. P. grangeri Brown & Schlaikjer 1943 MCW04, Tylosteus ornatus Leidy 1872 MCW04, P. reinheimeri Brown & Schlaikjer 1943 MCW04]

Stegoceras edmontonense (Brown & Schlaikjer 1943) MCW04 [=Troodon edmontonensis MCW04, Prenocephale edmontonensis S03, Stegoceras edmontonenis (l. c.) S03, S. edmontonensis S03, S. edmontonesis (l. c.) S03]

*Stegoceras validum Lambe 1918 S03, MCW04 [=S. validus (l. c.) S03, Troodon validus S03; incl. S. breve Lambe 1918 MCW04, Prenocephale brevis S03, S. brevis (l. c.) S03, S. lambei Sternberg 1945 MCW04, *Colepiocephale lambei S03, Troodon sternbergi Brown & Schlaikjer 1943 MCW04, Gravitholus sternbergi S03, *Hansuessia sternbergi S03, Stegoceras sternbergi S03]

*Sygimoloch spinifer Galton & Sues 1983 S03 [incl. Stenotholus kohleri Giffin, Gabriel & Johnson 1987 MCW04]

*Type species of generic name indicated


[D07] Dixon, D. 2007. The Complete Illustrated Encyclopedia of Dinosaurs & Prehistoric Creatures. Hermes House: London.

[MCW04] Maryańska, T., R. E. Chapman & D. B. Weishampel. 2004. Pachycephalosauria. In: Weishampel, D. B., P. Dodson & H. Osmólska (eds) The Dinosauria 2nd ed. pp. 464–477. University of California Press: Berkeley.

[S03] Sullivan, R. M. 2003. Revision of the dinosaur Stegoceras Lambe (Ornithischia, Pachycephalosauridae). Journal of Vertebrate Paleontology 23 (1): 181–207.

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