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Re: Neovenator (was Re: Allosauria redefined)



>At 03:34 PM 2/4/98 PST, you wrote:
>>I've just recently had the chance to take a good look at the 
>>*Neovenator* from Surrey, England, and there seems to be a real 
>>interesting allocation of this theropod to the African 
>>carcharodontosaurids. Perusing the skeleton, and matching it with 
>>similar skeletons, I've found that the closest match was with 
>>*Afrovenator*. There a list of synapomorphies, which include:
>>
>>*  broad scapula with shortend rectangular coracoid (Afro's is >>   
flanged at the end, while Neo's is not)

Basically, with polarity the subject, only tyrannosaurs share this, and 
we can pretty well agree that carnosaurs (my "allosaurs", but I'm coming 
around, Tom) were not coelurosaurian.

>(Trying for his best Obi Wan) "Learn about character polarity, 
>Jaemi..."

My user name is Jaemei, but my real name is Jaime. A bit of 
reconfiguring of the letters there, but it helps with the other language 
that the name [Jaemei] is based on, but they're pronounced the same.

>>*  ischium is long a slender with small obturator process, and has >>   
a distal boot (this feature is also shared with *Eustrepto-
>>   spondylus* from earlier beds (Oxford Clay) on the mainland)
>>*  the tibia has a very large cnemial process (another feature
>>   shared by a derived theropod, *Acrocanthosaurus*, to a greater
>>   degree and morphological similarity to that dinosaur)
>>*  the neural spines of the posterior caudals are hypershortened at
>>   the half point in the tail

>Again, check polarities.

>>*  the maxilla is elongate

>Damn, someone should really try clarifying exactly what is meant by 
>this... :-]

Sorry. I mean that the overall length of the bone compared to the height 
of the bone (the pre-antorbital height) is greater, and that this is 
true of carcharodontosaurids and all carnosaurs, but not to the singular 
degree seen in *Neovenator* and *Afrovenator*.

>>*  the naris is expanded posteroanteriorly

>A character common to many non-sinraptorid carnosaurs.

Hmmm. An interesting point. Means pretty much this isn't a good 
character, eh?

>>These synapomorphies

>Similarity does not equal synapomorphy.  Two forms may be more >similar 
to each other than to a third if the first two show the >primitive 
state, and the third the derived.  That does not suggest a >closer 
phylogenetic relationship between the two primitive forms.

Becklespinax shows similarity closer to Eustreptospondylus than other 
carnosaurs, based on the three vertebrae. The height of the neural 
spines are a derived feature, but there is enough 'morphy here to 
suggest a similar taxonomic standing (how do cladists say "family" 
without implying the Linnean system?).

Afrovenator shows a closer similarity to Acrocanthosaurus than to other 
carnosaurs in features I have earlier posted that coincidentally also 
imply a relationship closer to carcharodontosaurs than allosaurs. There 
are features in common with Acrocanthosaurus and Neovenator that would 
also imply a relationship with allosaurids, and by this make these two 
more similar (or polarizing taxa) but the relationship, I think, with 
Afrovenator cannot be denied, in that Afro may be the primitive form of 
the clade that groups Acro with Carc. Afrovenator shares more 
morphological characters with Neovenator than many other carnosaurs. My 
characters may have polarity, but each with a different group than all 
with one or just two, implying a closer relationship between those two.

I did admit that there may be problems with my grouping together of the 
two, but I feel that the number of characters supporting the group are 
more conclusive and compounding than the number supporting separation. 
As both forms are known from incomplete specimens, there may be some 
problems in gaining a full inventory of the connecting or disconnecting 
features.

Ah, well. As I took another look at the Afrovenator skeleton (the 
mounted one, though this mocks several bones including half the skull) I 
found another character that joins the two [Afro and Neo]: the pubis is 
double-curved, or that it curves forward, then down, and almost at 
extactly the same point on both pubes, something not seen in Allosaurus. 
As my photos of Acrocanthosaurus are not to keen on the nether regions 
of the body as the pubis and hindlimbs, I cannot tell if Acro is as 
similarly double-curved. Can you?

Oh, and as a double-check to my theory that I should have asked for long 
ago, what characters join Neo to Allo?

Jaime A. Headden

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