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Which other pachycephalosaur species did Spaherotholus goodwini & S. buchholtzae most resemble? Did they have a dome like Stegoceras, Prenocephale, or Pachycephalosaurus? Apparently, they seem to form a sister-group with Pachycephalosaurus & Stygimoloch, so I suppose they may have had domes that looked more like these two, right?

What bugs me is that the taxonomy of North American pachycephalosaurs seems so messy. HP Micky Mortimer provided me with valuable info some time back & helped me sort out the mess, but it appears that the describers of Sphaerotholus have differing opinions.

Here is the list of species Mickey Mortimer provided last May in response to some of my queries (thanks a lot mickey)

Stegoceras Lambe 1902
= Ornatotholus Galton and Sues 1983
S. validum Lambe 1902
= Troodon validus Gilmore 1924
= Stegoceras browni Wall and Galton 1979
= Ornatotholus browni Galton and Sues 1983
late Campanian, LC
Judith River Formation, Alberta, Canada
Comments- Ornatotholus has a parietal identical to Stegoceras and is
synonymous (Sullivan, 2000).
References- Sullivan, 2000. Stegoceras revisited. JVP 20(3) 72A

"Stegoceras" lambei Sternberg 1945
Comments- This taxon is a new genus (Sullivan, 2000).
References- Sullivan, 2000. Stegoceras revisited. JVP 20(3) 72A

Gravitholus Wall and Galton 1979
G. sternbergi (Brown and Schlaikjer 1943) Sullivan 2000
= Troodon sternbergi Brown and Schlaikjer 1943
= Stegoceras sternbergi
= Gravitholus albertae Wall and Galton 1979
late Campanian, LC
Oldman Formation, Alberta, Canada
Comments- Stegoceras sternbergi is the same as Gravitholus albertae, making
the new combination Gravitholus sternbergi (Sullivan, 2000).
References- Sullivan, 2000. Stegoceras revisited. JVP 20(3) 72A

Prenocephale Maryanska and Osmolska 1974
P. brevis (Lambe 1918) Sullivan 2000
= Stegoceras breve Lambe 1918
= Troodon brevis Hay 1930
late Campanian, LC
Judith River Formation, Alberta, Canada
syntype- (NMC 1423) (juvenile) frontoparietal dome
plesiotypes- (NMC 121) frontoparietal dome
(NMC 193) (juvenile) frontoparietal dome
(NMC 194) (juvenile) frontoparietal dome
(NMC 8819) (juvenile) frontoparietal dome
P. edmontonensis (Brown and Schlaikjer 1940) Sullivan 2000
= Troodon edmontonensis Brown and Schlaikjer 1940
early Maastrichtian-late Maastrchtian, LC
Horseshoe Canyon Formation, Alberta, Canada; Hell Creek Formation, Montana,

However, according to THOMAS E. WILLIAMSON, and THOMAS D. CARR, Gravitholus (which they affix the species name "albertae") is a Stegoceras, while Prenocephale edmontonensis is a nomen dubium and is referred to cf. Sphaerotholus sp.

Also, Prenocephale brevis & "stegoceras" lambei are still classified under Stegoceras.

This is messy. Which classification reflects the current consensus as to the taxonomy & phylogeny of North American pachycephalosaurs?

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