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my phylogeny, as of SVP'96 (long)
With all the talk of the other discoveries and papers at SVP, I haven't yet
gotten around to describing my new phylogeny. So, here it goes:
The subject was nonavian tetanurine phylogeny. Using Ceratosauria as the
closest outgroup, and various other dinosaurs as more distant outgroups to
polarize the characters, here are the results:
Piatnitzkysaurus and Eustreptospondylus are basal tetanurines, with E.
closer to the remaining forms.
My analysis found a (very weakly supported) Megalosauroidea (aka
Spinosauroidea, aka Torvosauroidea), with the structure Afrovenator +
(Megalosaurus + (Torvosaurus + Spinosauridae)). However, having seen some
of the illustrations of Baryonyx (the monograph comes out next year, folks!)
and talking with Angela Milner about spinosaurs in general, it turns out
many of the characters Sereno et al. and I have used to unite spinosaurids
with other basal tetanurines are not actually found in spinosaurids! For
example, they have quite large quadrate foramina. About all that holds this
grouping of basal tetanurines together are short forearms and big manual
digit I unguals. I suspect future analyses will leave Megalosaurus and
Torvosaurus as quite basal forms, that Spinosauridae will be closer to
avetheropods than to Torvosaurus (and thus, be neotetanurines), and that
Afrovenator may also be a neotetanurine, maybe even a basal carnosaur.
(In Milner's presenation, Spinosauridae was closer to Avetheropoda than to
Megalosaurus, and Torvosaurus was outside the Megalosaurus + (Spinosauridae
+ Avetheropoda) group).
Carnosauria, in this analysis, consists of Monolophosaurus + (Sinraptoridae
+ (an unresolved split between Acrocanthosaurus, Allosaurus,
Carcharodontosaurus, and Giganotosaurus)). I wouldn't be surprised if the
non-Allosaurus, non-Sinraptorid allosauroids fall out as a monophyletic
"Carcharodontosauridae", but my current study doesn't support it. I could
equally see an Allosaurus + Acrocanthosaurus and Carcharodontosaurus +
Giganotosaurus grouping falling out, and even have the latter closer to
sinraptorids than to Allosaurus. Neovenator and the new material of
Giganotosaurus may help sort this out.
As the most surprising (to me) aspect of the study, Gasosaurus came out as a
basal coelurosaur (i.e., closer to birds than to Allosaurus). Deltadromeus,
Dryptosaurus, and the recently-announced Bagarataan came out as more
advanced coelurosaurs, but ambiguous as to their relationship to each other
and to the maniraptoriform clades. Compsognathus and Ornitholestes were
found to be basal maniraptorans (as per Gauthier), with the more derived
maniraptorans comprising the as-yet-unnamed ((Oviraptoridae +
Elmisauridae/Caenagnathidae) + (Microvenator + (Alxasaurus +
Therizinosauroidea))) clade and the (Dromaeosauridae + (Archaeopteryx +
Ornithothoraces)) clade. In Arctometatatarsalia, Siamotyrannus was found
(on what can be determined) to be the sister taxon to Tyrannosauridae, and
Avimimus the sister to Troodontidae + (Pelecanimimus + Ornithomimidae). I
have not yet had time to study in detail the new alvarezsaurid or Coelurus,
so these were (unfortunately) left off. I am going to have to sit down with
the relevent material on Sigilmassaurus in order to see what is what before
I run it in the analysis.
That's pretty much it. There were quite a few other excellent dinosaur
posters at SVP, but unfortunately, we were only able to leave the posters up
between Thursday morning and 3:00 pm Friday: not enough time to absorb it all.
Thomas R. Holtz, Jr.
Vertebrate Paleontologist Webpage: http://www.geol.umd.edu
Dept. of Geology Email:firstname.lastname@example.org
University of Maryland Phone:301-405-4084
College Park, MD 20742 Fax: 301-314-9661
"There are some who call me... Tim."
-- Tim the Enchanter, "Monty Python and the Holy Grail"
---------- subtitle --[Monty Python ik den Holy Grailen]
"Tim?!? They called me TIM?!?!"
-- Tom the Paleontologist, on seeing "The Ultimate Guide to T. rex" :-)