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Re: Long-necked stegosaur, head tail mimicry?



David Marjanovic wrote:

> > This concept only came about fairly recently
> (c.1995),
> 
> Fourteen years ago is _not_ "fairly recently" in science.
> Really not.

It is "fairly recently" considering that the name was effectively coined back 
in 1956.  (On a paleotrivial note, Huene coined the clade Helopodinae even 
earlier, back when the genus was named _Helopus_.)

Also recall that Upchurch's 1995 concept of Euhelopodidae (_Euhelopus_, 
_Mamenchisaurus_, _Omeisaurus_) was reversed in 2004.  That's hardly longevity.


> Fine, but nobody used the name Euhelopodidae for anything
> else either, so whenever it was used, it was used for the
> assemblage Upchurch had found to be a clade.


See above.  Romer used it: he coined a Euhelopodinae back in 1956, and added an 
assemblage of genera to it.  


Doesn't matter.  We're simply talking content here.  It's ridiculous (IMHO) to 
claim that Euhelopodidae must include _Omeisaurus_ and _Mamenchisaurus_, when 
Romer's original group (erected nearly 40 years before Upchurch's study) 
included only one of these two genera, and also included genera that were not 
included by Upchurch (such as _Tienshanosaurus_).  The 'historical usage' 
argument cuts both ways.  I think Euhelopodidae is fair game for an updated 
content, and a phylogenetic definition to match.


> Not *Barosaurus*, which ended up with just nine dorsals --
> an outright neornithean value.


Yep, nice catch.  Thanks for that.  


> They _also_ add _really extra_ vertebrae into the neck that
> really are additional. Neomorphs -- perhaps genetic copies
> of neighboring vertebrae of something. 


Yes, I think you're right here.  These homeotic transformations are probably 
also behind the switch between procoelous, opisthocoelous and amphicoelous 
conditions in the tail vertebrae of derived titanosaurs, without the need for 
intermediate/incipient morphologies (amphiplatyan, etc).


Cheers

Tim