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RE: Armour Symposium Recollections



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Matthew Bonnan
>
> Tom Holtz was extremely enthusiastic, and I'm glad we have him
> here as our
> T. rex expert on the list.  I think if they had let him, he could
> have gone
> on for several hours and all of us at the symposium would have
> all been held
> in rapt attention.  Please keep up the enthusiasm, Tom!
>
Thanks!

Well, other people seemed to summarize a lot of the highlights of the other
speakers comments, so I suppose I should talk a bit about my own, but first
a few interesting comments by HP Currie (one from the Armour Symposium, one
from his talk on Sunday about feathered dinosaurs):

Phil Currie observed that _Aublysodon_-like teeth are more common in Lancian
sediments than in Judithian ones (although the type, _A. mirandus_, is
Judith River).  He proposed that perhaps these represent the premaxillary
teeth of juvenile _Tyrannosaurus_ and its closest relatives.  Yikes!
Interesting thought.  However, the problem remains that one might very well
be able to generate _Aublysodon_-type teeth by erosion and/or digestion of
run-of-the-mill tyrannosaurid-type premax teeth.

At the Feathered Dinosaur talk, Currie mentioned the possibility of naked
skinned tyrannosaurids!!  Apparently some skin impressions were found in
repreparation of the type of _G. libratus_ decades ago, and these lacked
mosaic scales.  Additionally, he said there are patches on some Dinosaur
Park specimens showing this.  As he mentioned, it may be that these
impressions are more common than we appreciate, but because they lack the
bumpiness of traditional dinosaur skin impressions they were missed by folks
for decades.  Unfortunately, no images of these impressions.  Much food for
thought...

As for my talk, the brief form:
* Tyrannosaurids very transformed theropods, and this has made them
difficult to place in theropod phylogeny (lacking, at least before, a tyrant
analog to _Archaeopteryx_)
* Inclusion of _Eotyrannus_ and _Stokesosaurus_ (and a couple others) to my
SVP2K matrix results in some changes:
        ** Tyrannosaurids are coelurosaurs, but lie outside Maniraptoriformes.
(Just outside, but outside).
        ** _Siamotyrannus_ (weakly), _Stokesosaurus_, and _Eotyrannus_ 
(strongly)
are supported as non-tyrannosaurid tyrannosauroids
        ** As such, it implies that features such as the midline iliac crest,
convergence of the ilia towards the midline, fully D-shaped premaxillary
teeth, elongate distal limb elements, and fused nasals occurred much earlier
in tyrant history than reduction of the forelimb, didactyly, and
arctometatarsality.

* A modified version of the tyrannosaurid matrix used to make my Tree of
Life page (which will be updated eventually to include this new info)results
in a tree with _Stokesosaurus_ outside _Eotyrannus_ plus Tyrannosauridae;
_Alectrosaurus_ outside _Alioramus_ plus Tyrannosaurinae; and a split
between an _Albertosaurus_-_Gorgosaurus_ clade and a _Daspletosaurus_ +
(_Tyrannosaurus_ + _Tarbosaurus_) clade.
        **Incidentally, there was agreement among the tyrannosaurid presenters 
on
the _Alb_+_Gorg_ vs. the Big Guys division.  HP Brochu did caution about the
possibility that the synapomorphies uniting _Tyr_ and _Tarb_ might be the
consequence of large size and shortened snouts in those two, and that
_Daspletosaurus_ may indeed be closer to _Tyr_ than is _Tarb_.

*Finally, the presence of tyrannosauroid premaxillary teeth
(?_Stokesosaurus_?) in Guimarota and in the Morrison (mis-identified as
"dromaeosaurid" teeth by Bakker in the Gaia volume) indicate that small
tyrannosauroids were around in the Late Jurassic.  This is to be expected if
tyrannosauroids are indeed outside Maniraptoriformes.

(Brief...  Well, I tried!).

I just want to end this by thanking the FMNH and the symposium organizers
for inviting us and taking care of us, and to say that I really enjoyed the
smaller scale, informal nature of this event.  Wish there were more venues
of this sort.

Back to writing evil nasty historical geology final exams... :-)

                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): 301-405-0796