Re: RE: Elaphrosaurus and Abelisaur Taxonomy

[Thomas_R_HOLTZ@umail.umd.edu (th81)]

>Nick Pharris asked for ideas about the taxonomy of Elaphrosaurus and the
>Abelisaurs (and some other critters I hadn't even heard of);
>
>Elaphrosaurus:  Personally, my inexperienced eye questions Gregory Paul's
>assignment of this genus to the ceolophyids.  I think he's right that it's
>not an ornithomimid.  Tom Holz (apprently Tim's twin ;) ) recently called it
                             ^
                            TZ.  That is H-o-l-T-z.  Americanized.

>an "Ornithomimid-mimic".  Gadzooks, what a mouthful!  I'd be interested to
>know if anyone has done a cladistic analysis which suggests this.

Umm, well... me.  In the 1994 paper, _E._ came out as the sister to
Abelisauridae, but in my more recent, MUCH larger matrix, it falls in a
trichotomy with _Dilophosaurus_ and Coelophyosidae, so it seems to be a
coelophysoid.

> It sounds as if the specimen is too fragmentary to really tell.

Not at all.  Sure, a skull would be nice, but it is very good for a Late J
small theropod in terms of completeness.

>Abelisaurs:  Someone mentioned recently that some of Greg Paul's (no, he is
>not my only reference!) Intertherapoda actually form a monophyletic clade.
>     Discussion:
>     1)  Torvosaurus (often placed at the next branching after Ceratosaurs
>one the family cladogram) have hypershortened forearms, as does
>Poikilopleuron (the humerus of which, as figured in _The Dinosauria_
>(Weishampel et al.) seems to preclude congenericity, which Paul (oops, here
>we go again) suggested in _PDW_ (Paul).  I do think he is on to something
>with Torvosaurus and Megalosaurus, though.).  This is a trait associated with
>Abelisaurs.

_Poekilopleuron_ may be _Megalosaurus_.  The case for a monophyletic
Megalosauridae (_Torvosaurus_, _Poekilopleuron_, _Megalosaurus bucklandi_)
is growing.

>     (Incidentally:  In _Hunting Dinosaurs_, Jim Jensen calls Torvosaurus a
>"big sauropod-killer", due to it's "large arms and big claws", good for
>"ripping through the tough hides of sauropods" [paraphrased].  I don't see
>how this is possible, considering it's really short forearms.

Short, but MASSIVE.  Huge muscle attachments.  Powerful claws.  Not at all
like the (grotesquely) shortened arms of _Carnotaurus_ (which, incidentally,
has a very well developed scapulocoracoid: for what,I have no clue).

>     2)  I'd like to know why Abelisaurs are placed in Ceratosauria.  They
>seem superficially similar to Ceratosaurus itself, but not the more derived
>Coelophysids.  They appear to have small pubic boots.  Then again, apparently
>so does Ceratosaurus.

Very small, in the case of _Ceratosaurus_.  The monophyly of Neoceratosauria
has been established in papers by Novas, Bonaparte, and me.

>     One interesting character the process which devides the orbit between
>the otic ring and the rest of the orbit formes a circle, and the center off
>the otic ring is set behind the posterior edge of the (ill-defined) bottom of
>the orbit.  This character seems to be present in Giganotosaurus as well.

And tyrannosaurids.  And _Acrocanthosaurus_.  This seems to arise
independantly in several large theropod taxa.

>     3)  Yangchuanosaurus seems too Allosauroid to be included.  I believe it
>is currently listed in the Sinraptoridae, closest to the Allosaurs (look at
>the maxillary process of the lacrimal).  It's Pubic boot is small, but it
>appears to have a obpturator [sic?] process on the ischium.

Drop the "p".  In any case, very well established as a sinraptorid
allosauroid.  See the Currie and Zhao 1994 (Canadian J Earth Sciences) and
Sereno et al. _Afrovenator_ paper in Science for details on sinraptorid and
allosauroid synapomorphies.

>     4)  Eustreptospondylus and Piatznykisaurus... pass

Unresolved basal tetanurines (Holtz 1996 abstract).

>     5)  Sarcosaurus, inconclusive.

Neoceratosauria indeterminate.

>     6)  How Paul Sereno comes up with Spinosauridae + Torvosauridae is
>beyond me.  He lists two characters for the clade (footnotes to the article
>on Eoraptor), one of which is hyper-enlarged manual digit I ungual, which I
>have never heard attributed to Torvosaurus.

Weakly supported clade, as he notes in the footnotes.  In my latest run, the
case for a Spinosauridae-Megalosauridae group drops out.

>     What I am guessing, and obviously this would have to be thoroughly
>worked out, is what I believe Nick and Tom Holz came up with a few weeks ago,

H-o-l-T-z.  Not to be snotty (okay, TO be snotty...), if you are going to
write about theropod systematics, you better learn how to spell my name... ;-)

Incidentally, just in case you don't know the reference:

Holtz, T.R., Jr.  1994.  The phylogenetic position of the Tyrannosauridae:
implications for theropod systematics.  Journal of Paleontology 64: 1100-1117.

>a clade characterized by increasingly shortened forearms, no opdurator
>process of the iscium (plesiomorphy), general absense of many tetanuran
>characters, and a small pubic boot which seems (and I know seems...) to be of
>equal size on both sides of the pubic shaft, and plesiomorhpic (downturned?)
>femoral heads.  Not much to go on.  If it could be proven, I think it would
>be appropriate to adopt Gregory Paul's terminology (sorry Mr. Paul), and
>label this group Intertherapoda, sister to Avetheropoda.

If they are monophyletic, and if you use a superfamily "rank" (as have
Sereno et al.), then the proper name is "Megalosauroidea" (since the
presence of _Megalosaurus_ tends to supercede all later taxonomic names).
If you were to use a non-superfamilial name, then "Intertheropoda" is the
only one out there, although Greg's taxon was paraphyletic.

>     The big problem here is that most of these characters (except the arms)
>are primitive to theropods, and it always seems that earlier Tetanurae were
>very conservative of body plan, and I'm not sure there will be enough
>evidence to ever prove or disprove early relationships amongst them.

Got that right!

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661

"There are some who call me...  Tim."