RE: Sequential Centrosaurines, Batman!

["Andrew A. Farke" <andyfarke@hotmail.com>]

> -----Original Message-----
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu] On Behalf 
> Of Jaime A. Headden
> Sent: Tuesday, May 18, 2004 8:44 PM
> To: dinosaur@usc.edu
> Cc: twilliams_alpha@hotmail.com
> Subject: Re: Sequential Centrosaurines, Batman!
> 
> Tim Williams (twilliams_alpha@hotmail.com) wrote:
> 
> <BTW, the diagnostic characters of _Brachyceratops_ are thought by 
> some authors to be immature centrosaurine characters, and therefore
invalid.
> Ditto for _Monoclonius_.  Thus, both genera are deemed invalid under 
> this interpretation.>
> 
>   Yes. However, juveniles _can_ exhibit diagnostic features, even if 
> the juvenile condition cannot be compared to adults of other species 
> (reducing their diagnostic utility). The actuality of the features 
> that are present as unique in combination or existence, or as a 
> dinosaur, ornithischian, or ceratopsian, etc., makes these features 
> valuable and useful, even if the naming of the taxon is pushing it. 
> Otherwise, *Chasmosaurus canadensis,* *Brachyceratops montanus,* and 
> *Monoclonius crassus* are valid in their uniqueness, but hardly 
> comparable to the adult types and almost completely adult hypodigms of 
> other ceratopsians. Skulls referred to *Monoclonius* include the 
> species *M. lowei* and *M. dawsoni,* the former which is distinct from 
> both *Centrosaurus* and *Styracosaurus,* as well as other 
> centrosaurines, based on its frill morphology, and indicate they are 
> possible unique species, even if they may not validate the genus they were
placed it.
> 

I strongly recommend that anyone interested in this topic consult Sampson et
al., 1997. To summarize (and somewhat contradict what Jaime said), many (if
not most) of the features of juvenile ceratopsians are *not* diagnostic. A
juvenile centrosaurine is a juvenile centrosaurine is a juvenile
centrosaurine. Hence, the sinking of Brachyceratops and many of the
Monoclonius species.

SAMPSON, S. D., M. J. RYAN, AND D. H. TANKE. 1997. Craniofacial ontogeny in
centrosaurine dinosaurs (Ornithischia: Ceratopsidae): taxonomic and
behavioral implications. Zoological Journal of the Linnean Society,
121:293-337.

Of course, this is not to say that juveniles can't have features diagnostic
to species (e.g., Nanotyrannosaurus/Tyrannosaurus), but just that
ceratopsian juveniles often don't.

Andy