Re: Quaesitosaurus and Nemegtosaurus

[Nick Longrich <longrich@stardot.com>]

On Tue, 10 Dec 1996 Dinogeorge@aol.com wrote:

> In a message dated 96-12-09 17:52:40 EST,
> T.Williams@cclru.randwick.unsw.edu.au (Tim Williams) writes:
> 
> > It's worth noting that Upchurch's cladistic analysis regarded
> > _Opisthocoelicaudia_ not as camarasaur or even a diplodocoid, but as
> > a titanosaur.  The postcranial skeleton of _O._ has a close OVERALL
> > similarity to camarasaurids, but when it comes down to the nitty-
> > gritty, there's not too many synapomorphies linking the two
> > together. 
> 
> Alas, I disagree with Upchurch's self-admittedly debatable placement of _O._
> among the titanosauroids. It's no more a titanosauroid than segnosaurs are
> theropods. 

        There's one character- that 1st toe- which convincingly argues your 
point. To explain this we can invoke some argument about the evolution of a 
graviportal animal from a cursor perhaps requiring a reversal of the 
whole digit reduction thing, and it's not like weirder things haven't 
happened (e.g. the hoatzin) so that's hardly impossible. Nor is the 
evolution of herbivory or backwards pointing pubes since both happened in 
the theropods before in ornithomimes and dromaeosaurs respectively, the 
pubes may have done so independently in Mononykus too, if it is as you 
argue closer to ornithomimes than modern birds. 
        If we want to propose segnosaurs as non-theropod, we must ask 
why a lineage not related to theropods would evolve 
a long-fingered, big-clawed tridactyl manus with a semilunate carpal 
bloc,  a booted pubis  and that birdlike v1 nerve opening when none of 
these characters are known from outside the group? Should we even 
seriously entertain the idea of nontheropod  segnosaurs when these 
features have not yet been explained convincingly, 
if even at all, in context of this hypothesis?

        Nick L.