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RE: Horner's Pachy Lumpin' - Your Thoughts?



> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] 
> On Behalf Of Michael Erickson
>
> >You also made claim that Triceratops horns are longest in adults. Do 
> >you know this for certain? How many Triceratops skulls have 
> you looked 
> >at (even in photos)?
> 
> Tons, as _Triceratops_ is one of my favorite dinosaurs. I 
> have never seen a young individual with horns bigger than an 
> adult's, if anyone else has feel free to point it out. 
> Everything I've seen indicates that the horns are biggest in 
> adults and very late subadults.

http://www.dinosaures-web.com/images/dino/triceratop_horns.jpg

That said, a scatterplot of a lot of skulls would be very nice... (Thanks
for the shoutout, Ralph!)

> Tom Holtz wrote:
> 
> >Another ceratopsid case of metaplasia: the postorbital and 
> nasal horns 
> >ofyoung Pachyrhinosaurus are indeed horns, but as they aged the 
> >postorbital horns get resorbed and remodeled into pits and the nose 
> >horn into the distinctive mound.
> 
> I've heard a lot about this but can never find a reference. Anyone...?
> 
Currie, P. J., Langston, Jr., W., Tanke, D. H., 2008. A New Horned Dinosaur
from an Upper Cretaceous Bone Bed in Alberta. NRC Press. 152pp. ISBN-13
9780660198194.

SCOTT D. SAMPSON, MICHAEL J. RYAN & DARREN H. TANKE. 1999. Craniofacial
ontogeny in centrosaurine dinosaurs (Ornithischia: Geratopsidae): taxonomic
and behavioral implications. Zoological Journal of the Linnean Society. 121:
293-337
(http://www3.interscience.wiley.com/cgi-bin/fulltext/120802209/PDFSTART)

> Don Ohmes wrote:
> 
> >There may not be an extant analogue, but so what? Is there a 
> dinosaur 
> >that grew annual antler-analogs? Should we assume one existed, just 
> >because we now have elk?
> 
> That's a weak argument right there. No one has even compared 
> dinosaurs to mammals until you just did. I totally ignored 
> mammals, actually, focusing on reptiles and birds. But 
> anyway, I think that the fact that no extant organism more 
> derived than a fish seems to grow in such a manner is a bit 
> too weighty an argument to be cast off automatically. It's 
> not conclusive, to be sure, but it is suggestive (just how 
> suggestive is open to debate, but still).
> 
> I find that the EPB has been pretty much ignored in this 
> discussion, something I find peculiar. Just a few weeks ago 
> many were stating that it is most parsimonious to conclude 
> that _Sinornithosaurus_ did not posess a venomous bite, based 
> on the EBP*. Why doesn't it apply here? Why isn't it most 
> parsimonious to conclude that pachycephalosaurids did not 
> grow in this manner, considering that no extant reptile or 
> bird does? Is it because Horner and Goodwin's arguments are 
> considered conclusive enough to trump parsimony? If so, then 
> I would beg to differ, of course.

The EPB is used for inferring traits otherwised not observed and for showing
the relative support for inferring these traits (level I: both members of
the bracket have it; level II: only one does; level III: neither do). It is
NOT a guide to utterly exclude traits in the fossil form, particularly if
other lines of evidence (such as histological ones) apply.

And the Erickson et al. papers and their spin offs HAVE demonstrated that
there are peculiarities of growth in Mesozoic Dinosauria that are not
present in Mammalia, Testudines, Lepidosauria, Crocodylia, and living Aves.

> Has anyone else on the list noticed that _Stygimoloch_ is 
> exactly the same size as _Dracorex_?:
> 
>
http://upload.wikimedia.org/wikipedia/commons/0/05/Pachycephalosaurus_ontoge
ny.png
> 
> I know Bakker et al. 2006 noted it, but it doesn't seem to 
> have received much attention otherwise.

Actually, doi:10.1371/journal.pone.0007626.t001

All that being said, an actual adult Dracorex specimen or a juvenile
Pachycephalosaurus that isn't Stygimoloch and/or Dracorex would end this
debate really damn quick.

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