Re: Antetonitrus

["Tim Williams" <twilliams_alpha@hotmail.com>]

Matthew Bonnan wrote:

> For someone who is not a systematist, these changes in phylogenetic 
> interpretation lead to a whole new series of functional ramifications.  
> Call them whatever you like, and argue about what they should be called, 
> but what Yates, Kitching, and some others have been doing is prodding the 
> rest of us into re-
> evaluating the beginnings of the largest dinosaur giants, and that to me is 
> what is most significant about this recent announcement.

Adam Yates wrote:

> To Tim I would say that Lessemsaurus, Blikanasaurus and Anchisaurus HAVE 
> got a whole lot more sauropod-like.

I agree with both statements (and everything else said by Matt and Adam) 
wholeheartedly.  Above _Saturnalia_-_Thecodontosaurus_- _Efraasia_ there 
would appear to be a split in sauropodomorph evolution, with one line 
leading to sauropods (via _Anchisaurus_ and melanorosaurids) and the other 
leading to plateosaurs.  I find this fascinating - not the least of which 
because it implies a shift from bipedality to increased quadrupedality 
occurred independently in both lines.

Anchisaurids are indeed more sauropod-like than plateosaurs.  However, 
myself (and I believe Mickey too) were trying to douse any suggestion that 
by putting _Anchisaurus_ in the Sauropoda that this critter had suddenly 
become a big, lumbering, broad-footed quadruped.  My point was that the 
inclusion of _Anchisaurus_ in the Sauropoda is *not* due to the fact that it 
fits the archetypal view of a "sauropod" - after all, _Anchisaurus_ is still 
a modest-sized slender-limbed runner.  Rather, _Anchisaurus_ finds itself in 
the Sauropoda because of its new place in sauropodomorph phylogeny, which 
means that it is now captured by the phylogenetic definition of the 
"Sauropoda".  I think this is terrific, and I see no reason why the term 
Sauropoda should be re-defined because it includes non-traditional sauropods 
like _Anchisaurus_.

As for the other basal sauropods... In contrast to _Anchisaurus_, 
melanorosaurids and blikanasaurids have long been considered 
"sauropod-like".   Both families did include hefty-sized, broad-footed, 
lumbering quadrupeds.   The question has been whether or not the 
sauropod-like traits of melanorosaurids and blikanasaurids indicated a close 
relationship to sauropods, or were due to convergence.  The excellent work 
of Yates and Kitching indicates the former.  Great stuff!




Tim

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