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RE: Ceratops analyzed in the Sampson et al. (2010) matrix
Tim Williams wrote-
> > Well, it found Torosaurus and Triceratops (and Nedoceratops) to be
> > sister taxa. They were entered as separate OTUs, so their distinction
> > was assumed by the authors. But being sister taxa in the cladogram is
> > just as congruent with the hypothesis they're synonymous.
> What's the bootstrap support? Unless it's high, then you effectively have a
Doesn't matter. Even if the cladogram had a polytomy between Triceratops,
Torosaurus and their sister taxon (e.g. Eotriceratops), that's still congruent
with the former two being synonymous. There has to be support against
Triceratops and Torosaurus forming a unique clade for there to be support
against their synonymy.
> > At worst,
> > this could make Utahceratops a junior synonym of Ceratops.
> Never gonna happen.
Only because of cultural reasons. Scientifically, since there's no objective
definition of genus, any sister species could be placed in the same genus.
> > As for Eoceratops, Longrich notes the long brow horns and hooked
> > squamosal distinguish it from Chasmosaurus, but he doesn't say anything
> > about comparison to Agujaceratops or other long-horned ceratopsines.
> > Just because a specimen is juvenile is not a reason to ignore it as a
> > holotype.
> Given the poor track record of ceratopsians that have immature specimens as
> their holotypes (_Brachyceratops_, _Monoclonius_), then I think we have
> strong grounds to regard _Eoceratops_ as a nomen dubium.
> Just to be clear... I'm not arguing that ALL genera based on
> juvenile/immature specimens should be dismissed as nomina dubia. Otherwise
> _Apatosaurus_ would be sunk in favor of _Brontosaurus_. Hmmm... now there's
> an idea. ;-)
I think each case should be examined separately. Brachyceratops (which is
Rubeosaurus based on stratigraphy if nothing else) may be equally consistant
with being a juvenile Rubeosaurus or Achelousaurus, but it does not follow that
Eoceratops is equally consistant with being a juvenile Mojoceratops or
Agujaceratops. Taxa don't all share the same ontogenetic timing for the
development of diagnostic characters.