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RE: Ceratops (was RE: Glishades ericksoni, ...)



Tim Williams wrote:
>
> Paul P <turtlecroc@yahoo.com> wrote:
>
>> Nah. Ceratopsidae is a great name for that clade because,
>> again, Ceratops is likely a basal form, i.e. near the root
>> of Centrosaurinae + Chasmosaurinae,
>
>
> Yep, _Ceratops_ may indeed be "near the root of
> Centrosaurinae+Chasmosaurinae".  But is _Ceratops_ inside or outside this
> clade?  This is what I'm driving at.
>
>
> Because unless _Ceratops_ is actually *within* the
> Centrosaurinae+Chasmosaurinae clade, then it is NOT a ceratopsid.  In
> other words, to qualify as a ceratopsid, _Ceratops_ must lie inside the
> clade specified by _Triceratops_ and _Centrosaurus_ (or
> _Pachyrhinosaurus_, depending on whose definition of Ceratopsidae you
> use).
>
>
> _Triceratops_ is a chasmosaurine, and _Centrosaurus_ and
> _Pachyrhinosaurus_ are centrosaurines.  Thus, you cannot have either a
> non-chasmosaurine ceratopsid or a non-centrosaurine ceratopsid.  So there
> cannot be a "basal ceratopsid" that does not belong to either the
> Chasmosaurinae or Centrosaurinae.

It depends on what the agreed upon definition of Ceratopsidae is to be. If
it is (for example) Centrosaurus + Chasmosaurus, than Ceratops might well
be a non-ceratopsid. If instead Ceratopsidae is defined as Ceratops +
Centrosaurus + Chasmosaurus, than it would be included by definition, but
might be outside Chasmosaurus > Centrosaurus and Centrosaurus >
Chasmosaurus.

This is basically the situation that Prieto-Marquez advocates:
Hadrosauridae = Hadrosaurus + Saurolophus + Lambeosaurus; Saurolophinae =
Saurolophus > Lambeosaurus; and Lambeosaurinae = Lambeosaurus >
Saurolophus. In his phylogeny, Hadrosaurus is a hadrosaurid but neither a
saurolophine nor a lambeosaurine.

-- 
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
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Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
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                        University of Maryland
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