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RE: Ceratopsine phylogeny questions



I think this will be exciting as a paper once we get to see it - did not
make it to England, so did not see the talk. So I can happily mention what I
would expect without inferring at all that the authors didn't or won't meet
my expectations.

It is important to note just how tricky it will be to back up the assertion
they are making. In papers where authors are trying to do significant
clumping (something I have done), it is important to show insignificant
differences in the characters that were used to discriminate the taxa
involved in the first place. If the argument here is mostly showing that
Torosaurus is a natural extension of Triceratops allometrically, that is
really not enough to show they are the same as taxa within the same family
often show very congruent growth patterns and share allometric trajectories.
So demonstrating something as the same taxon rather than the result of some
heterochronic mechanism is the trick and will necessitate lots of
discussion. So I would hope, and anticipate, the talk, and the resulting
paper will have extensive allometric analyses and discussions of these
factors. Will be fun.

Ralph

-----Original Message-----
From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] On Behalf Of
Thomas R. Holtz, Jr.
Sent: Wednesday, October 07, 2009 11:30 AM
To: tehdinomahn@live.com; dinosaur@usc.edu
Subject: RE: Ceratopsine phylogeny questions

> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] 
> On Behalf Of Michael Erickson
>
> Tim Williams wrote:
>  
> > So "genera" such as _Brachyceratops_ and _Monoclonius_ are 
> regarded as 
> > nomina dubia
>  
> Hate to be a party crasher here, but Dodson (1992) showed 
> that _Monoclonius_ was a vlid genus. _Brachyceratops_, 
> however, is indeed a jeuvenile of some other centrosaurine, 
> probably _Styracosaurus_.
>  
> Ref.
>  
> Dodson, Peter (1992). On the status of the ceratopsids 
> _Monoclonius_ and _Centrosaurus_. In: Dinosaur systematics: 
> Approaches and Perspectives. Cambridge University Press. pp. 
> 231 - 245. ISBN 0521438100.

Not universally accepted by any means, in light of more recent discoveries
of centrosaurine populations.

> > On that basis, _A. ajax_ would be regarded as a nomen dubium. This 
> > would render>_Brontosaurus_ a valid genus,

But Iff that basis (that juveniles weren't acceptable as types, which they
currently are) were accepted. Sad to say, the case for _Brontosaurus_ is not
particularly good...

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Earth, Life & Time Program, College Park Scholars
http://www.geol.umd.edu/~jmerck/eltsite/
Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA