PBDB Taxon

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Morphology	Ecology and taphonomy	External Literature Search	Age range and collections

Pachycephalosaurus

Reptilia

Taxonomy

Pachycephalosaurus was named by Brown and Schlaikjer (1943). Its type is Troodon wyomingensis.

It was assigned to Troodontidae by Brown and Schlaikjer (1943); to Ornithopoda by Ostrom (1965); to Domocephalinae by Sereno (1986), Goodwin et al. (1998); to Pachycephalosaurinae by Sereno (1997), Sereno (1998), Sereno (1999), Sereno (2000), Williamson and Carr (2003), Williamson and Carr (2006), Williamson et al. (2009); to Pachycephalosauridae by Sternberg (1945), Romer (1956), Tatarinov (1964), Kuhn (1964), Estes (1964), Romer (1966), Charig (1967), Swinton (1970), Maryańska and Osmólska (1974), Thulborn (1974), Galton (1974), Bonaparte (1978), Dong (1978), Wall and Galton (1979), McIntosh (1981), Dodson (1983), Russell (1984), Breithaupt (1985), Clemens (1986), Sues and Galton (1987), Russell (1987), Carroll (1988), Maryanska (1990), Olshevsky and Ford (1994), Sues (1997), Eberth (1997), Eberth et al. (2001), Maryanska et al. (2004), Butler et al. (2008), Schott et al. (2009); to Eupachycephalosauria by Dieudonné et al. (2020); and to Pachycephalosaurini by Sullivan (2003), Sullivan (2006), Goodwin and Evans (2016), Woodruff et al. (2021).

Species

P. wyomingensis (syn. Stygimoloch spinifer, Stenotholus kohleri, P. grangeri, Dracorex hogwartsia, P. reinheimeri, Tylosteus ornatus)

Synonyms

Stygimoloch was named by Galton and Sues (1983).

It was synonymized subjectively with Pachycephalosaurus by Goodwin and Evans (2016).

It was assigned to Pachycephalosaurinae by Sereno (1999), Sereno (2000), Williamson and Carr (2003), Williamson and Carr (2006); to Pachycephalosauridae by Galton and Sues (1983), Russell (1984), Clemens (1986), Sues and Galton (1987), Carroll (1988), Maryanska (1990), Olshevsky and Ford (1994), Sues (1997), Goodwin et al. (1998), Maryanska et al. (2004), Schott et al. (2009); and to Pachycephalosaurini by Sullivan (2003), Sullivan (2006), Woodruff et al. (2021).
Stenotholus was named by Giffin et al. (1988).

It was synonymized subjectively with Stygimoloch by Maryanska (1990), Goodwin et al. (1998), Sullivan (2003), Maryanska et al. (2004), Sullivan (2006), Williamson and Carr (2006).

It was assigned to Pachycephalosauridae by Giffin et al. (1988).
Tylosteus was named by Leidy (1872).

It was considered a nomen oblitum by Baird (1979), Sues and Galton (1987); it was synonymized subjectively with Pachycephalosaurus by Galton and Sues (1983), Maryanska (1990), Maryanska et al. (2004).

It was assigned to Lacertilia by Leidy (1873); to Lacertilia by Zittel (1890); to Amphisbaenidae by Hay (1902); to Ankylosauridae by Hay (1930); and to Acanthopholididae by Kuhn (1964).
Dracorex was named by Bakker et al. (2006).

It was synonymized subjectively with Pachycephalosaurus by Williamson et al. (2009), Goodwin and Evans (2016).

It was assigned to Pachycephalosaurini by Sullivan (2006), Bakker et al. (2006), Woodruff et al. (2021).

Synonymy list

Year	Name and author
1872	Tylosteus Leidy p. 40
1873	Tylosteus Leidy p. 285
1890	Tylosteus Zittel p. 610
1902	Tylosteus Hay p. 477
1930	Tylosteus Hay p. 239
1943	Pachycephalosaurus Brown and Schlaikjer pp. 132-133
1945	Pachycephalosaurus Sternberg p. 535
1956	Pachycephalosaurus Romer p. 632
1964	Pachycephalosaurus Estes p. 144
1964	Pachycephalosaurus Kuhn p. 30
1964	Tylosteus Kuhn p. 44
1964	Pachycephalosaurus Tatarinov p. 589
1965	Pachycephalosaurus Ostrom p. 39
1966	Pachycephalosaurus Romer p. 370
1967	Pachycephalosaurus Charig p. 716
1970	Pachycephalosaurus Swinton p. 231
1974	Pachycephalosaurus Galton p. 1064 fig. 6
1974	Pachycephalosaurus Maryańska and Osmólska p. 47
1974	Pachycephalosaurus Thulborn p. 173
1978	Pachycephalosaurus Bonaparte p. 569
1978	Pachycephalosaurus Dong p. 227
1979	Pachycephalosaurus Wall and Galton p. 1183
1981	Pachycephalosaurus McIntosh p. 35
1983	Pachycephalosaurus Dodson p. 95
1983	Stygimoloch Galton and Sues
1984	Pachycephalosaurus Russell p. 27
1984	Stygimoloch Russell p. 27
1985	Pachycephalosaurus Breithaupt p. 169
1986	Pachycephalosaurus Clemens p. 80
1986	Stygimoloch Clemens p. 80
1986	Pachycephalosaurus Sereno
1987	Pachycephalosaurus Russell p. 10
1987	Stygimoloch Sues and Galton
1987	Pachycephalosaurus Sues and Galton p. 30
1988	Pachycephalosaurus Carroll
1988	Stygimoloch Carroll
1988	Stenotholus Giffin et al.
1990	Pachycephalosaurus Maryanska p. 566
1990	Stygimoloch Maryanska p. 566
1994	Pachycephalosaurus Olshevsky and Ford p. 91
1994	Stygimoloch Olshevsky and Ford p. 91
1997	Pachycephalosaurus Eberth p. 202
1997	Pachycephalosaurus Sereno p. 440 fig. 2
1997	Pachycephalosaurus Sues p. 512
1997	Stygimoloch Sues p. 512
1998	Stygimoloch Goodwin et al. p. 363
1998	Pachycephalosaurus Goodwin et al. p. 371
1998	Pachycephalosaurus Sereno p. 62
1999	Pachycephalosaurus Sereno p. 2138 fig. 2
1999	Stygimoloch Sereno p. 2138 fig. 2
2000	Pachycephalosaurus Sereno pp. 500-501 fig. 25.8
2000	Stygimoloch Sereno pp. 500-501 fig. 25.8
2001	Pachycephalosaurus Eberth et al. p. 66
2003	Pachycephalosaurus Sullivan p. 198
2003	Stygimoloch Sullivan p. 199
2003	Pachycephalosaurus Williamson and Carr fig. 11
2003	Stygimoloch Williamson and Carr fig. 11
2004	Pachycephalosaurus Maryanska et al. p. 465
2004	Stygimoloch Maryanska et al. p. 466
2006	Dracorex Bakker et al. p. 331
2006	Dracorex Sullivan p. 357
2006	Pachycephalosaurus Sullivan p. 357
2006	Stygimoloch Sullivan p. 359
2006	Pachycephalosaurus Williamson and Carr p. 323
2006	Stygimoloch Williamson and Carr p. 323
2008	Pachycephalosaurus Butler et al. p. 8
2009	Stygimoloch Schott et al. p. 781 fig. 8
2009	Pachycephalosaurus Schott et al. p. 783 fig. 8
2009	Pachycephalosaurus Williamson et al. p. 291
2016	Pachycephalosaurus Goodwin and Evans p. 3
2020	Pachycephalosaurus Dieudonné et al.
2021	Dracorex Woodruff et al. p. 588 fig. 14
2021	Pachycephalosaurus Woodruff et al. p. 588 fig. 14
2021	Stygimoloch Woodruff et al. p. 588 fig. 14

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Rank	Name	Author
kingdom	Animalia	()
—	Bilateria
—	Eubilateria	Ax 1987
—	Deuterostomia
phylum	Chordata	Haeckel 1874
subphylum	Vertebrata
superclass	Gnathostomata
—	Osteichthyes	()
subclass	Sarcopterygii	()
subclass	Dipnotetrapodomorpha	(Nelson 2006)
subclass	Tetrapodomorpha	()
—	Tetrapoda
—	Reptiliomorpha
—	Anthracosauria
subclass	Amphibiosauria	Kuhn 1967
—	Cotylosauria	()
—	Amniota
—	Sauropsida
class	Reptilia
subclass	Eureptilia	()

Rank	Name	Author
—	Romeriida
—	Diapsida	()
—	Archosauromorpha	(Huene 1946)
—	Crocopoda
—	Archosauriformes	Gauthier 1986
—	Eucrocopoda
—	Archosauria	()
informal	Avemetatarsalia
—	Ornithodira
—	Dinosauromorpha
—	Dinosauriformes
—	Dinosauria	()
—	Ornithischia	()
—	Genasauria
—	Cerapoda
—	Marginocephalia
—	Pachycephalosauria	()
—	Eupachycephalosauria
genus	Pachycephalosaurus

If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.

G. †Pachycephalosaurus Brown and Schlaikjer 1943

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†Pachycephalosaurus wyomingensis Gilmore 1931

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Invalid names: Dracorex hogwartsia Bakker et al. 2006 [synonym], Pachycephalosaurus grangeri Brown and Schlaikjer 1943 [synonym], Pachycephalosaurus reinheimeri Brown and Schlaikjer 1943 [synonym], Stygimoloch spinifer Galton and Sues 1983 [synonym], Tylosteus ornatus Leidy 1872 [synonym]

Invalid names: Dracorex Bakker et al. 2006 [synonym], Stygimoloch Galton and Sues 1983 [synonym], Tylosteus Leidy 1872 [synonym]

Diagnosis

No diagnoses are available

Measurements

No measurements are available

Composition:

hydroxyapatiteo

Entire body:

yesg

Adult length:

10 to < 100o

Adult width:

1.0 to < 10o

Adult height:

1.0 to < 10o

Maximum body mass:

1000 kgg

Minimum body mass:

30 kgg

Architecture:

compact or denseo

Ontogeny:

accretion, modification of partso

Grouping:

gregariouso

Environment:

terrestrialo

Locomotion:

actively mobileo

Life habit:

ground dwellingo

Diet:

herbivoreo

Reproduction:

oviparouso

Dispersal:

direct/internalo

Dispersal 2:

mobileo

Created:

2005-08-25 05:50:23

Modified:

2005-08-25 07:50:23

Source: g = genus, o = order

References: Peczkis 1995, Marsh 1875

Age range: base of the Maastrichtian to the top of the Lancian or 72.10000 to 66.00000 Ma

Collections (30 total)

Time interval	Ma	Country or state	Original ID and collection number
Late/Upper Campanian	83.5 - 70.6	Canada (Alberta)	P. sp. (59222)
Maastrichtian	72.1 - 66.0	USA (Montana)	P. grangeri (47627) P. sp. (88987 88988) Predentata indet. (48848) Stenotholus kohleri (12977) Stygimoloch spinifer (47626 48844 48845 48846)
Maastrichtian	72.1 - 66.0	USA (North Dakota)	Stygimoloch spinifer (48843)
Maastrichtian	72.1 - 66.0	USA (South Dakota)	Dracorex hogwartsia (58813)
Lancian	70.6 - 66.0	USA (Wyoming)	P. sp. (72145) Stygimoloch spinifer (14544)
Lancian	70.6 - 66.0	USA (Montana)	P. sp. (14616) Stygimoloch spinifer (14550)
Late/Upper Maastrichtian	70.6 - 66.0	USA (Colorado)	P. sp. (49539)
Late/Upper Maastrichtian	70.6 - 66.0	USA (Wyoming)	P. grangeri (14585) P. sp. (26760) P. wyomingensis (64644) Triceratops sp. (64645) Troodon wyomingensis (52106)
Late/Upper Maastrichtian	70.6 - 66.0	Canada (Alberta)	P. sp. (168404)
Late/Upper Maastrichtian	70.6 - 66.0	USA (South Dakota)	P. sp., Dracorex hogwartsia (224484) P. wyomingensis, P. reinheimeri (47628)
Late/Upper Maastrichtian	70.6 - 66.0	USA (Montana)	P. sp. (183110) P. wyomingensis (52904 152397 161171) Tylosteus ornatus (91359)