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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 
> polytomy.

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.

Mickey Mortimer