RE: Isanosaurus question

["Williams, Tim" <TiJaWi@agron.iastate.edu>]

Mickey Mortimer wrote:

> Not at all.  No one ever claimed sauropods were the direct descendents
> of Melanorosaurus or Riojasaurus.  In fact, a Melanorosauridae including
> those genera is not universally accepted by sauropodomorph workers.

Ah, but a clade called Melanorosauridae would have to include
_Melanorosaurus_.  ;-)  The question is, do the heavy-set four-footed
prosauropods (e.g. _Riojasaurus_, _Melanorosaurus_, _Camelotia_) constitute
a monophyletic group?  If Sereno's work is any guide, then many of the
characters traditionally used to define the Melanorosauridae may be
primitive (symplesiomorphous) sauropodomorph characters.  If true, the
Melanorosauridae is out the window with a loud crash.

(The situation isn't helped by the fact that the big-ass prosauropods like
_Melanorosaurus_ and some Chinese taxa are either poorly known or poorly
described.  For example, I doubt that "_Melanorosaurus" thabanensis_ even
belongs in the same genus as the type, _M. readi_.) 

One possibility for the Prosauropoda is that (say) the group is paraphyletic
relative to the Sauropoda and a monophyletic group comprising _Plateosaurus_
and its closest relatives.  


> Just like deinonychosaurs can be the sister group of birds (even 
> ignoring the Jurassic teeth). 

Exactly right - contra the "temporal dysjunction" nonsense spouted by some
folks who (either in ignorance or mischief) conflate the terms 'ancestor'
with 'sister taxon'.  Case in point: "Deinonychosaurs lived AFTER
_Archaeopteryx_, so how can they be the ancestors of birds???" Answer:
"Deinonychosaurs are the sister group of birds, NOT the ancestors - just as
chimpanzees didn't give rise to humans." 


Tim

------------------------------------------------------------ 

Timothy J. Williams 

USDA-ARS Researcher 
Agronomy Hall 
Iowa State University 
Ames IA 50014 

Phone: 515 294 9233 
Fax:   515 294 3163