Re: Marshosaurus

[NJPharris@aol.com]

In a message dated 97-08-31 18:12:03 EDT, znc14@ttacs1.ttu.edu (Jonathan R.
Wagner) writes:

> >The obturator notch in the pubis of _M. bicentesimus_ is rather more open
>  >(and _Allosaurus_-like) than in known sinraptorids.
>          This could have something to do with ontogeny...

Is there good evidence that the animal that the _Sinraptor_ skeleton belonged
to was consederably younger when it died than _Marshosaurus_ or _Allosaurus_?


>  >The ischium compares very favorably to _Allosaurus_, having a triangular 
> base
>  >and a prominent, proximally-placed obturator flange.  As in _Allosaurus_,

> the
>  >ischiadic rod is long, straight, slender, and flared distally.  In this
>  >respect it is rather more like the ischium of _Allosaurus_ than like
those 
> of
>  >sinraptorids, which are broader and bear a hook at the end.
>          Of course, the pelves of the sinraptorids are highly variable,
>  having both primitive- and allosaur-like morphologies in the same clade.

Let's get our terms straight.  What exactly do you inlcude in Sinraptoridae?
 Also, see below.


>  >Theropod pelves are far more diagnostic than most people give them credit
>  >for!
>          While I have been a big proponent of this in the past, every time
I
>  compare pelvic morphology to phylogeny, I come up short. 

Odd that I don't.


>  Look
>  at the case of _Yangchuanosaurus_ and _Sinraptor_. With only the pelves,
>  what would you say about them?

I would say that the pelvis of _Yangchuanosaurus_ has been very poorly
reconstructed in the past.  In all the drawings I've seen, the ilium is
missing the laterally-directed wing at the front of the preacetabular
process.  Also, since at the time of _Yangchuanosaurus_'s description, no
other carnosaurs were known with a hook bounding the pubic foramen, so the
foramen was illustrated as fully enclosed.  If the pictures I've seen of the
actual specimen are trustworthy (I know, a big if, but check it out), the
pubic foramen is bounded by a hook (Norman's _Illustrated Encyclopedia of
Dinosaurs_, pg. 67).  The ischium compares favorably with that of _Sinraptor_
(although it looks like the obturator flange is obscured behind the femur).

>          On the other hand, I agree with you in this one case. Marsho seems
>  likely to be a carnosaur. Now, if you wanna wrangle, we can talk
>  _Stokesosaurus_, but check the archives first...

Looks rather similar to _Megalosaurus_ to me, although it also bears a
passing resemblance to tyrannosaurids (unlikely given the time frame) and to
_Piatnitzkysaurus_.

NP

P.S. Watch for my new address:  pharrinj@plu.edu