Re: STRANGE THEROPOD SKULLS

["Jaime Headden" <jaemei@hotmail.com>]

<<<The pelvis may not be a great diagnostic feature in theropods.>>>

<<Actually, it's very diagnostic. Especially the ischium. I've stated 
this before on the list. Strait as opposed to curved (and which 
direction it is curved); booted or not, laterally compressed or 
expanded; possession of a dorsal ridge (indicative of sinraptorids); 
obturator flange as opposed to obturator prong (or primitive to advanced 
gradient); long or short subacetabular puboischial symphysis; large, 
small, deep, shallow, narrow, and/or wide ischial peduncle (is this the 
right term for the ilial-ischial articulation?). I'm in the process of 
formulating a table of characters exclusive of pelves that also include 
other basal tetanurines and advanced ceratosaurs and "megalosaurs", for 
variation and comparison.>>

<It can be of some value when defining a species or seperating a 
species, but not for a whole group.>

Generally, but of all "allosaurs" like *Marshosaurus*, *Allosaurus*, and 
*Saurophaganax*, there is a slender ischium that is distolaterally 
expanded into a sort of "boot". There is a dorsal ridge (as stated 
before) on sinraptorids and *Afrovenator*. "Megalosaurs" like Meggie and 
Torvo have inwardly curved ischia with compressed "feet", as do several 
other of my basal "carnosaurs" like *Eustreptospondylus* et al.

<<But you're right, too. It's not a great character, but in the abscence 
of a skull or braincase for _the_ most indicative characters, the pelvis 
provides the number-two character set that is almost as good as the 
cranium. Also, better to use when you lack braincases to examine.>>

<Perhaps, but the pelvis has some function that increasingly changes 
it ( the hindlimb musclature ). So it may not be a very good diagnostic 
character.>

The femora of most "carnosaurs" I listed are diagnostic are all mostly 
strait, have a raised fourth trochanter near to the epiphysis, a large 
medially or forward-set lesser trochanter, and a raised femora head. A 
few lack some of these characters (e.g., *Gasosaurus*) and these almost 
all occur in the Jurassic, with the most advanced (or derived) forms 
appearing in the Cretaceous (carcharodontosaurs, Afro, spinosaurs and 
dryptosaurs).

These femora occur on pelves that have all long ischia with booted ends, 
unlike the short ischia of ceratosaurs (not neoceratosaurs like 
abelisaurs and *Ceratosaurus*, which may be tetanurans, but thats a 
different thread) or the short unbooted ischia of coelurosaurs.

<<<Baryonyx and Megalosaurus may have some relation but you cannot base 
it on some general similiarities.>>>

<<Oops. I meant this to assume a basal tetanurine status for Meggie, 
excluding him from the Ceratosauria. But size of skull compared to body 
size is interesting to note [could be indicative of diet alone, 
though).>>

<Oh, yes.>

Then maybe I should see how similar the maxillae and dentaries of 
*Baryonyx* and *Megalosaurus* are to each other. Or Afro and Bary with 
Spino, like I should have done. Good point, Paul.

<<<Function-related parts of the body can look extremely similiar in 
unrelated animals with similiar lifestyles.>>>

Also true.

<<Elongated ischium (as in any of my carnosaurs) are very similar to 
each other, sure, but not so inclusive of ceratosaurs, coelophysoids, 
and Coelurosaurs. This only refines the grouping (see below).>>

<Elongate ischium are also found in therizinosaurs.>

A good case for convergence, and this would in turn supply us with a 
case for convergence within my Carnosauria that would invalidate it. 
Another good point.

<<Piat may be a basal allosauriform, Mono an allosauroid basal to both 
sinraptorids and allosaurids and more advanced than Cryo (actually, 
nearly all carnosaurs are more advanced than Cryo).>>

<In what features? Crylophosaurus may be lacking one or two allosaur 
features, but that does not mean a close relationship.>

But Cryo does occur earlier than most other carnosaurs, and has features 
both primitive and those considered "carnosaurian"; pneumatic lachrymals 
without lachrymal foramen, a combo of primitive and carnosaurian. The 
pelvis was described, but not figured, and I don't know if the photos of 
the specimen show it, since I haven't seen them. Glut (1997) cites 
Hammer and Hickerson (1994) in saying the femoral head declines from the 
greater trochanter, where the opposite is diagnostic for carnosaurs, the 
extensor groove on the back of the femur is shallow, and both characters 
are diagnostic for coelophysoids; there is a fusion of the ankle bones 
resulting in a tibiotarsus, indicative of neoceratosaurs. The posterior 
ramus of the angular extends to the rear of the mandible, with the 
ventral process of the surangular invading the angular's lateral 
surface, creating a "bulge" that is seen only in sinraptorids. The orbit 
is invaded dorsally by processes from both the lachrymal and 
postorbital. Otherwise, other characters of the skull can be either 
neoceratosaurian or "megalosaurian"

This dinosaur seems to represent one of the best examples of a 
transistory taxon, truly between one group and the other.

<<Notes: *Chilataisaurus* may be a carcharodontosaur~>>
 
<May be a basal allosaur too.>

<<*Bahariasaurus* may not~>>

<Bahariasaurus is "sunk" down to the position of basal coelurosaur, 
Deltadromeus.>

Based on material later refered to the first taxon. But I must admit, 
the type ischium of Baharia does appear to have coelurosaur qualities: a 
triangular obturator flange and short distus.

<<*Szechuanosaurus* could be an allosaurid~>>

<I think that it has been argued in was a tyrannosaur (could be 
mistaken.)>

Not exactly the best material to base an analysis on (a tooth) whereas 
the refered skeleton should have been parsimoniously given it's own 
name. 

<<all taxa listed below *Allosaurus* could be genuine or junior
  synonyms of that famous form~

  *Allosaurus* may be junior ro *Antrodemus*~>>

<No way. Or at least over my dead body.>

This may lead to a *Rioarribasaurus*-*Coelophysis*--type problem. The 
holotype specimen may be two different taxa, however, so both diagnoses 
may be valid.

<<*Afrovenator* may be a derived member of Sinraptoridae and still 
preclusive of carcharodontosaurs, thus uniting Carcharodontosauroidea 
and Sinraptoridae into Carcharodontosauriformes, where "Carch" is older 
thus has precedence~>>

<Ugh! Afrovenator is a torvosaur, related to spinosaurs. It lacks all 
allosaur apomorphies. Carcharodontosaurs and sinraptorids are closely 
related.>

That Torvo may be a carnosaur could make this problematic. And I guess I 
must be a stubborn cuss, but I hold to Afro's carnosaurian nature. The 
lachrymal foramen is lacking in Torvo and Meggie, the tooth is flat 
laterally and thus bladelike in a form that is nearly identical to 
allosaurs (and even carcharodontosaurs, though not "wrinkled" or evenly 
serrated). The pubis is double-curved as in Eustrepto (another possible 
torvosaur) and *Neovenator*. There is a maxillary fenestra, nasal 
participation in the antorbital fossa [assumed: no nasals known]. The 
cnemic process of the tibia is ceratosaurian, though, and unusual for a 
Cretaceous (Barremian-Hauterivian?) dino unless it were a Neoceratosaur 
(which torvosaurs may be). Form of humerus is allosaurian.

A comparison of Afro with Bary and Spino is in need, and I will try to 
do so.

<<Not listed are possible Tetanurans Abelisauria.>>

<I still stick with Neoceratosaurians.>

I'm not sure, but that may be the more parsimonious taxon.


Welcome back, Paul!

Jaime A. Headden

______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com