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). In basal members of the group, such as Homalocephale calathocercos, the dorsal surface of the skull was relatively flat, but in the derived Pachycephalosauridae it became high and dome-shaped.

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)
                              `--+--Prenocephale Maryańska & Osmólska 1974 S03
                                 |    `--*P. prenes Maryańska & Osmólska 1974 S03
                                 |--Tylocephale Maryańska & Osmólska 1974 MCW04
                                 |    |--T. bexelli D07
                                 |    `--T. gilmorei Maryańska & Osmólska 1974 MCW04
                                 `--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.

Last updated: 5 August 2017.

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