Discussion of Deltadromeus and Carcharodontosaurus

From: jrw6f@faraday.clas.virginia.edu

If you have access to CNN, go to it now! "I found another skull" Sereno et al. just had their press conference about their new African theropods. I cannot remember the details (T. Holtz, can you enlighten us with species names). The "spidery allosaur" is an impressive beastie, with extremely long arms (therizinosaur/deinocheirid-like? My roommate saw them and asked "it's quadrupedal?"), a *HUGE* pectoral girdle, and very gracile. The "huge charcharodont" is very aberrant, with a very sharp snout and an elongate naris. It's skull is larger than T. rex. The CNN commentator very pointedly said that it "ambushed it's prey", which makes me wonder... See the news, read the article in Science, wish YOU had the grant money...

The CNN story can be found at: http://cnn.com/TECH/9605/17/dinosaurs/index.html on the web. This includes a reasonable shot of the big guy, which the article identifies as Charcarodontosaurus. Looks heavily reconstructed. Features:

• Invasion of postorbital bone into the orbit (orbit shaped like Giganotosaurus)
• Rostro-caudally elongate enlarged external naris
• Rostro-dorsal inclination of quadratojugal-squamosal articulation(?)
• Scalpel-shaped maxillary tooth row.

Boy does it look Carnosaur!

From: Thomas_R_HOLTZ@umail.umd.edu (th81)

I have seen the original paper for this, though I missed Paul Sereno's press conference (I was typing in my Environmental Geology exam at the time...).

The skull is referable to Carcharodontosaurus saharicus. It is a GIGANTIC skull, although the exact figure of 1.6 m rests on the size of the (currently unknown) premaxilla. Scaling up from the previous specimen, this guy should have a 1.45 m femur (marginally bigger than Giganotosaurus).

Sereno et omnia recognize a monophyletic Carcharodontosauridae (with Acrocanthosaurus and Giganotosaurus), as one part of an allosauroid polytomy (the other branches being Sinraptoridae, Cryolophosaurus, Monolophosaurus, and Allosaurus). This matches very well with my abstract for SVP this year, so it's nice to see we're all on the same track in this part of the clade...

The second theropod is a basal coelurosaur, Deltadromaeus agilis. No skull material, whopping huge coracoids, an unpinched oviraptorid-like foot, and similar in many ways to Bahariasaurus. I hope they find a claw: I suspect it might be somewhat (if not very) similar to Dryptosaurus. They place it as closer to other coelurosaurs than is Ornitholestes, but Compsognathus is still conspicuous by its absence...

There is a phylogenetic data matrix in this paper (THANK YOU!!), so I've got to go through those and add new ones to the ever-more ponderous matrix of mine.

Paul and company, if you are reading this: On behalf of dinosaur paleontologists everywhere, Thank you! These are wonderful new additions (and clarifications) to our understanding of theropod phylogeny and dinosaur biogeography.

(For those interested, the specimens are from the Kem Kem region of Morocco, and are Cenomanian in age, contemporaneous with Giganotosaurus.)

The authorship is Sereno, Duthiel, Iarochene, Larsson, Lyon, Magwene, Sidor, Varrichio, and Wilson. Theropod taxonomists will not forgive this team when we have to type out the trinomial Deltadromaeus agilis Sereno, Dutheil, Iarochene... 1996! :-)

From: Thomas_R_HOLTZ@umail.umd.edu (th81)

Peter Buchholz writes:

>I have a question about Sereno's new theropod
>called Deltadromeus. He says it is a Coelurosaur (in the proper
>sense), but not what kind. Does anyone know what of Coelurosaur it
>is? Is it possible that it is related to Baryonichids, Spinosaurids,
>Irritatorids or Troodontids? I would think that that might be a

Those first three are all really the same clade. Lack of serrations on teeth which are otherwise indistinguishable does not rank (;-) up there as justifying a new family, in my humble opinion.

Deltadromeus seems to be more like Ornitholestes or Dryptosaurus than any of those others you mention. And, of course, there is no strong evidence for the coelurosaurian, much less bullatosaurian, nature of the spinosaurs.

Sereno et omnia place it closer to "other coelurosaurs" than to Ornitholestes. (A parenthetical comment: Why aren't my fellow theropod systemacists including Compsognathus in their cladograms? It's not exactly a poorly known or poorly described taxon, and there are some excellent casts (e.g., the Yale Peabody cast) in North America!).

From: Dinogeorge@aol.com

Peter Buchholz writes:

>I have a question about Sereno's new theropod
>called Deltadromeus. [etc., see above]

Tom Holtz suggested a close relationship with Dryptosaurus (Cope's Laelaps) from the Maastrichtian of New Jersey. I'm quite inclined to agree with him because of the general proportions of the hind limbs of Deltadromeus and Dryptosaurus, but to clinch it I'd like to see a picture of a Dryptosaurus metatarsal III: if it's >>not<< pinched, we've got a good case for referring Deltadromeus to Dryptosauridae.

From: Thomas_R_HOLTZ@umail.umd.edu (th81)

George Olshevsky wrote:

>...I'd like to see a
>picture of a Dryptosaurus metatarsal III

So would I, since that element isn't currently known!!

The anatomy of mts II and IV suggest that it *could* be moderately pinched, but not as far as a good arctomet foot.

The humeri of Deltadromeus and Dryptosaurus are similar, as well.

From: NJPharris@aol.com

In a message dated 96-05-31 11:49:06 EDT, Jonathan Wagner wrote:

>...I believe, but I'm not sure,
>that this is part of the Charcharodontosaurus-as-abelisaur theory that has
>been put up (I believe Holtz, mentions it in the big paper (1994)).

No, I don't believe so. In this month's National Geographic, Sereno is pretty committal in labeling Carcharodontosaurus an allosauroid. Based on what I've seen, I have to agree. *Very* close to Acrocanthosaurus, and closer to Sinraptoridae than to Allosauridae, IMHO. I still haven't seen the new paper. What's the ref? [It's the cover story of the May 17th issue of Science -- MR]