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RE: Doesn't George have a point? and the "Pachy Paradox Problem"



Trying to get multiple responses in here, then something new:

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> NJPharris@aol.com
>
> > Is it in line with
> >  prevailing standards of scientific analysis of
> >  prehistoric life to hypothesize that birds are
> >  dinosaur descendants when the dinosaurs the birds are
> >  said to have descended from come after the first birds
> >  in the known fossil record?
>
> Yes, it is.  "Prevailing standards of scientific analysis" do not
> look for
> ancestors; they look for relatives.

Precisely.  In fact, the news article by Stokstad in Science did a bit of a
condensation of my quote.  While in print it says: ""They're not playing the
game," says Tom Holtz", I had gone to elaborate: "They're still playing the
'find the ancestor' game, while most of the rest of us have moved on to the
'search for the sister taxon' approach."

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Dinosaur Interplanetary Gazette
>
> Does someone have a reference for an online cladistic diagram
> that shows the
> lineage for both of these models?
>
By "both of these models", do you mean George's BCF vs Gauthier's or mine or
Sereno's or Sues & Makovicky's or...?  I don't know if George has one
online, so hopefully he'll post one.  The Dinosauria.com site and the
Dinosauricon have various versions of the coelurosaur cladogram, as does my
intro to dinosaurs class site:
http://www.geol.umd.edu/~tholtz/coelclad.htm or
http://www.geol.umd.edu/~tholtz/104Lec25.htm, for examples.

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Dinogeorge@aol.com
>
> An interesting question is, What happened at the
> Jurassic-Cretaceous boundary
> that eliminated the less birdlike theropods and permitted the
> OODT theropods
> to take over those niches?

I wouldn't say "eliminated": _Scipionyx_ and _Nedcolbertia_ and the Wealden
forms and _Bagaraatan_ do not seem to be nearly as bird-like as the OODT
(aka non-avian maniraptoriform) theropods, for example.

Now, as for a new take on the "temporal paradox".  The following is entirely
analogous to the argument used by the Feducciaries, but since it concerns
creatures less beloved (to most people, although not to Ralph Chapman!!!)
than birds nobody tries to use it to overturn ornithischian systematics.
Okay, here it goes:

"How can those (nasty rotten ideologically flawed) cladists say that
pachycephalosaurs are ceratopsian ancestors!!  Don't they know that
pachycephalosaurs don't show up until the Late Cretaceous, but ceratopsians
are now known from the Middle Jurassic?  You can't be older than your
Grandma, you know!!"

[To translate this into the bird argument, change "pachycephalosaurs" to
"dromaeosaurids" and "ceratopsians" to "birds" (which, I admit, would be a
helluva transformation!).]

This argument might have some weight, if the dirty nasty filthy cladists
were actually ARGUING that pachycephalosaurs were ceratopsian ancestors.
But we're not: studies place them as the sister group rather than the
ancestors.  What the distribution does show is that the pachycephalosaur
record sucks relative to the ceratopsian record, but no more than that.

P.S.  Astute readers will note another similarity to the Feduccia-style
argument: the total dismissal of the Early Cretaceous.  Just as they don't
acknowledge the presence of good dromaeosaurids (like _Sinornithosaurus_ or
_Utahraptor_ or _DEINONYCHUS_, for heavens' sake!!) from the Early
Cretaceous, the Pachy Paradox problem as stated ignores the possible
presence of Pachycephalosauria, in the form of _Stenopelix_ (argued to be a
pachycephalosaur by Sereno in his 1999 paper in Science), in the Early
Cretaceous.

Hope this helps to put things into perspective.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-314-7843