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Re: Sphaerotholus



Dino Rampage (dino_rampage@hotmail.com) wrote:

<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.>

  *Gravitholus* was originally always *G. albertae*, whereas
*Ornatotholus* is *O. browni*. It was *Stegoceras edmontonense*, rather,
as Sullivan's work is hardly an exemplary of systematic structure, rather
provenance and "gross" similarity. *Prenocephale* is best restricted to
type *P. prenes* and has close affinities to *Tylocephale*, wheres species
of *Stegoceras* are united on the basis of several features, including
restriction of the frontal dome with paired grooves above the
supraorbitals/prefrontals and a posterior parietal with a shelf dorsally
that is absent in *Prenocephale*, but is also found in other
pachycephalosaurs. Even "Ornatotholus" has this posterior "shelf" and
frontal lateral "grooves" in the dorsal surface. Sullivan's referral of
*Stegoceras sternbergi* to *Gravitholus* is similarly rejected, and the
species along with *Gravitholus*, are indicated as having shared derived
features with *Stegoceras* (contra Sullivan) and are indicated as
*Stegoceras* sp. (this does not mean they represent an unnamed species,
but that they definately belong to *S.* or the complex of species referred
to under that name, and each cannot be established on enough material to
qualify for a requisite diagnosis sufficient to distinguish it clearly
from other species of pachycephalosaurs). *Ornatotholus* and *Gravitholus*
are considered nomina dubia as a result of the relative immaturity of the
material and its brevity in the types.

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

  Williamson and Carr. At 55 characters, it is the most comprehensive
analysis of pachycephalosaurids to date, beating out Sereno's because his
(1999) was a Marginocephalia tree in general. Much of this is supplemented
by a clear understanding of the braincase anatomy. Nearly the same
phylogeny was found with Sereno's tree, however, and the enormous amount
of differences result from species ascription to *Stegoceras* and the
amount of non-diagnostic or partial material included.

  *Sphaerotholus*, the first real "bowling-ball" pachy.Other pachy domes
were either very narrow and peaked, or were egg-shaped, and in
*Prenocephale*, seem to have been developed into three separate dome
regions (paired caudal progressing into a single midline rostral
dome-let).

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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