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Clade
Subclade

Taxon
Taxon
Pachycephalosauria
Nominal Author
Maryanska and Osmˇlska 1974
2nd Nominal Author
Taxon Status ACTIVE
Comments
The active definition is a first-order revision of that initially proposed by Sereno (1998) and revised recently by Maryanska et al. (2004). Unlike these earlier versions, it includes several other species as external specifiers to maintain taxonomic content in the face of alternative phylogenetic arrangements. Ceratopsians may be the nearest outgroup, but this is far from certain.
Potential Synonomy

Active Phylogenetic Definition
Active Definition
The most inclusive clade containing Pachycephalosaurus wyomingensis (Gilmore 1931) but not Triceratops horridus Marsh 1889, Heterodontosaurus tucki Crompton and Charig 1962, Hypsilophodon foxii Huxley 1869, Ankylosaurus magniventris Brown 1908.
Shorthand
> Pachycephalosaurus wyomingensis but not Triceratops horridus, Heterodontosaurus tucki, Hypsilophodon foxii, Ankylosaurus magniventris.
Definitional Author
Sereno 2005
Definition Status checked
Definition Type STEM
Node-Stem Triplet STEM
Other Triplet Taxa
Marginocephalia, Ceratopsia
Specifiers
Specifier(s) A
Pachycephalosaurus wyomingensis
Specifier(s) B
Specifier(s) C
Triceratops horridus, Heterodontosaurus tucki, Hypsilophodon foxii, Ankylosaurus magniventris
Qualifiers
+Taxon
-Taxon
Datum
Taxonomic Content
Publication Year Unknown
Unknown
Unknown
1998

Inactive Taxon Status
Rejection Criteria
Critique
 

Definitional History #1
Earliest Record
All marginocephalians closer to Pachycephalosaurus than to Triceratops.
Latest Record
Sereno 1998:62
Range (My)
Range (My)
Pachycephalosaurus, Triceratops
Range (My)

Definitional History #2
Earliest Record
All the taxa more closely related to Pachycephalosaurus wyomingensis than to Triceratops horridus.
Latest Record
Maryanska et al. 2004:464
Range (My)
Range (My)
Pachycephalosaurus wyomingensis,Triceratops horridus
Range (My)

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