Re: Newcomer (Male) with a few things to share (2nd attempt)

[David Marjanovic <david.marjanovic@gmx.at>]

> > Guaibasaurus basal to Eoraptor and herrerasaurids?
>
> Different analyses placed it as either a basal saurischian or an early 
> type
> of theropod. I decided to compromise between them and make it the
> basalmost theropod.

This is not how science works. There's a whole philosophical book with the 
title "The truth does not lie in the middle". There is evidence that 
*Guaibasaurus* is a non-eusaurischian saurischian, and there is evidence 
that it is a basal theropod, but there is no evidence for anything else. 
Your compromise would amount to the addition of a third hypothesis.

> There really doesn't appear to be much material known from it, so
> it is pretty hard to place.

Well, the original description placed it at the base of Saurischia based on 
a few general similarities, while the Basal Saurischia chapter in The 
Dinosauria II finds it as the basalmost theropod based on an actual 
cladistic analysis. I'll trust the latter for the time being. It makes quite 
good sense -- *G.* looks like a theropod, except that its first metatarsal, 
although arguably thinned, still reaches the ankle.

> (note to self: don't trust the
> popular media when it comes to dinosaurs)

I agree.

> Interesting. It seems that coelophysids are pretty distinct when compared 
> to
> Herrerasaurus, but Eoraptor shares a few characteristics with them that 
> are
> lost in Herrerasaurus. Could Herrerasaurus have lost them through
> convergence or could it possibly be more closely related to Dilophosaurus?
> (I doubt the latter is true)

All these seems to assume that *Eoraptor* and *Herrerasaurus* are theropods. 
While the picture is certainly not clear, the majority of the evidence (as 
explained in the book chapter mentioned above) has both of them as basal 
saurischians, in the position where *Guaibasaurus* was originally thought to 
lie, with *Eoraptor* as the sister-group of Eusaurischia:

Dinosauria
 |--Ornithischia
 `--Saurischia
      |--Herrerasauridae
      `--+--*Eoraptor*
         `--Eusaurischia
              |--Theropoda
              `--Sauropodomorpha

"+" is an unnamed clade.

> The skeletal reconstructions I found made Liliensternus look like a 
> slightly
> smaller and more gracile version of Dilophosaurus, with the skull larger
> relative to the body than in Coelophysis and deeper as well, but not as 
> much
> as in Dilophosaurus.

That's fine, but these are just two characters...

> Though Rauhut did have a monophyletic Coelophysidae, it
> did show a gradual progression from smaller, more gracile forms like
> Coelophysis into larger, more robust ones like Liliensternus, and I 
> thought
> Dilophosaurus would work well as a "next logical step" if things kept 
> going
> the same direction.

It is quite dangerous to rely on "trends". Things tend to diversify rather 
than to keep going in a direction.

> (relationships within Titanosauria are
> kind of messy for one)

Quite so! There has never been an analysis of all known titanosaurs (known 
at any particular time when an analysis could have been made, I mean). Part 
of the reason is that many do not overlap in known material.