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.: Heishansaurus Bohlin 1953MCW04, D07
    |           `--H. pachycephalus Bohlin 1953 (n. d.)MCW04
    |--Stenopelix Mayer 1857MCW04
    |    `--S. valdensis Meyer 1857MCW04
    `--+--Wannanosaurus Hou 1977MCW04
       |    `--W. yansiensis Hou 1977MCW04
       `--Goyocephala [Homalocephalidae]MCW04
            |--Goyocephale Perle, Maryańska & Osmólska 1982MCW04
            |    `--G. lattimorei Perle et al. 1982MCW04 [=Stegoceras lattimoreiP10]
                |--Homalocephale Maryańska & Osmólska 1974MCW04
                |    `--H. calathocercos Maryańska & Osmólska 1974MCW04
                `--+--Ornatotholus Galton & Sues 1983MCW04
                   |    `--*O. browni (Wall & Galton 1979)S03 [=Stegoceras browniMCW04]
                   `--Pachycephalosauridae [Pachycephalosaurinae, Pachycephalosaurini, Tholocephalidae]MCW04
                        |  i. s.: ‘Troodon’ bexelli Bohlin 1953MCW04 [=Stegoceras bexelliS03]
                        |         Gravitholus Wall & Galton 1979MCW04
                        |           `--*G. albertae Wall & Galton 1979 (n. d.)S03
                        |         Yaverlandia Galton 1971B93, MCW04
                        |           `--Y. bitholus Galton 1971MCW04
                        |--Stygimoloch Galton & Sues 1983 [incl. Stenotholus Giffin, Gabriel & Johnson 1987]MCW04
                        |    `--*S. spinifer Galton & Sues 1983S03 (see below for synonymy)
                        `--+--Stegoceras Lambe 1902 [incl. Colepiocephale Sullivan 2003, Hanssuesia Sullivan 2003]MCW04
                           |    |--*S. validum Lambe 1918S03, MCW04 (see below for synonymy)
                           |    `--S. edmontonense (Brown & Schlaikjer 1943)MCW04 (see below for synonymy)
                           `--+--Pachycephalosaurus Brown & Schlaikjer 1943 [incl. Tylosteus Leidy 1872]MCW04
                              |    `--*P. wyomingensis (Gilmore 1931)S03 (see below for synonymy)
                              `--+--Prenocephale Maryańska & Osmólska 1974S03
                                 |    `--*P. prenes Maryańska & Osmólska 1974S03 [=Stegoceras prenesP10]
                                 |--Tylocephale Maryańska & Osmólska 1974MCW04
                                 |    |--T. bexelliD07
                                 |    `--T. gilmorei Maryańska & Osmólska 1974MCW04 [=Stegoceras gilmoreiP10]
                                 `--Sphaerotholus Williamson & Carr 2002MCW04
                                      |--S. buchholtzae Williamson & Carr 2002MCW04
                                      |--S. edmontonenseD07
                                      `--S. goodwini Williamson & Carr 2002MCW04 [=Prenocephale goodwiniS03]

*Pachycephalosaurus wyomingensis (Gilmore 1931)S03 [=Troodon wyomingensisMCW04; incl. P. grangeri Brown & Schlaikjer 1943MCW04, Dracorex hogwartsiaP10, Tylosteus ornatus Leidy 1872MCW04, P. reinheimeri Brown & Schlaikjer 1943MCW04]

Stegoceras edmontonense (Brown & Schlaikjer 1943)MCW04 [=Troodon edmontonensisMCW04, Prenocephale edmontonensisS03, Stegoceras edmontonenis (l. c.)S03, S. edmontonensisS03, S. edmontonesis (l. c.)S03]

*Stegoceras validum Lambe 1918S03, MCW04 [=S. validus (l. c.)S03, Troodon validusS03; incl. S. breve Lambe 1918MCW04, Prenocephale brevisS03, S. brevis (l. c.)S03, S. lambei Sternberg 1945MCW04, *Colepiocephale lambeiS03, Troodon sternbergi Brown & Schlaikjer 1943MCW04, Gravitholus sternbergiS03, *Hansuessia sternbergiS03, Stegoceras sternbergiS03]

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

*Type species of generic name indicated


[B93] Benton, M. J. 1993. Reptilia. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 681–715. Chapman & Hall: London.

[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.

[P10] Paul, G. S. 2010. Dinosaurs: A Field Guide. A & C Black.

[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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