Re: Opisthocoelicaudia (was Re: Titanosaurids)

["Jaime A. Headden" <qilongia@yahoo.com>]

George Olshecksy (dinogeorge@aol.com) wrote:

<No, it was Nothronychus (before its description), which was the first 
segnosaur in which there was a preserved furcula, together with a better 
description of the segnosaur foot (Sereno, pers. comm.) than was available
the literature. The furcula carries a lot of weight in theropod
systematics, and it was enough to push me over the line: so, segnosaurs
are theropods convergent on prosauropods rather than prosauropods
convergent on theropods.>

  The problem here is, that although I feel that *Beipiaosaurus*, with
it's in situ furcula, is the only known segnosaur with one. The element
first proposed as a furcula in *Nothronychus* is not, but rather an
anterior fused pair of median grastralia, which is accompanied by several
others. Only one segnosaur has them preserved. However, I had thought the
case had been made on *Beipiaosaurus'* shoulder and foot.

<If something like that turns up in Opisthocoelicaudia, I'll change my
mind. But right now, there's just not enough evidence that O. is a
titanosaur for me to alter my opinion.>

  Ah ... hadn't the analysis of Curry-Rogers and Forster allowed this to
settle much differently? I wonder if people are seriously ignoring the
*Rapetosaurus* paper.... They showed that *Nemegtosaurus* and
*Opisthocoelicaudia*, in the only analysis to include them both _and_ be
published (I think Mickey Mortimer tried them together in Upchurch's
matrix [a man who has wavered and is now in cahoots with Wilson on
something]) where both titanosaurs and occupied _different_ parts of the
titanosaur tree. Salgado and Calvo, in a morphological analysis, suggest
that it is so advanced as to lie next to the saltasaurines, well above
nemegtosaurs. This is indicated in the scapulocoracoid, ulna, and femoral
morphologies. Many basal theropods have variant sacral incorporation, so
which one is a neosacral is irrelevant, really ... so much about
*Opisthocoelicaudia* is unique no matter where it goes that it would be
difficult to assume what's relevant and what's not. There's only one way o
fully test all the features at once, and right now, that's a data matrix
run through a numeric algorithm machine.

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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