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Re: Lumping Spinosauridae Redux



Mike Taylor (mike@indexdata.com) wrote:

<Here's my take on this.  To define any kind of higher group, in these
enlightened days, we need at least two specifiers: either two ingroups
(for a node) or an ingroup and an outgroup (for a stem).  (Here I am
ignoring apomorphy-based clades, and quite right, too.)  The magic of the
"genus" (and the "species", which is arguably no less illusory for fossil
animals) is that you're allowed to define it on only one specifier. 
(Actually, you don't have to define it at all, but if you do, you only
need one specifier.)  For example:

* Species _Baryonyx walkeri_ = specimen BMNH R9951 and all other  
individuals that are pretty damned similar to it.>

  This is how J. Clarke has been defining her species.

<* Genus _Baryonyx_ = specimen BMNH R9951 and all other individuals that
are quite similar to it but not necessarily _that_ similar.> 

  I don't understand ... how similar is "not too similar"? What's the
metric?

<* Clade Baryonychinae = (_Baryonyx_ > _Spinosaurus_)>

  I think the first approximation of this name was Baryonychidae,
transfered as a synonym of Spinosauridae when Sereno coined
"Baryonychinae" in his analysis. If one follows the ICZN, Charig and
Milner are the authors of the name Baryonychinae. I would follow the name
of earliest precedence that was used to separate *Baryonyx* from
*Spinosaurus,* i.e., Baryonychidae. The name ending in -inae is excessive
and useless.

<Given these definitions, you can find morphological evidence that the
type of _Suchomimus tenerensis_ belongs in Baryonychinae, but how could
you possibly have "evidence" that it either does or doesn't fit into
_Baryonyx_ or _Baryonyx walkeri_?>

  If its autapomorphies appear to belong to a broader clade. Hutt
described a vertebra from the Isle of Wight that purports to do this,
indicating *Baryonyx* had a dorsal "sail" -- normally the neural spines in
the posterior dorsal vertebrae in the type are only 2/3 the vertebral
height, but this element is over 4x the vertebral height, almost
intermediate in size between *Baryonyx* and *Suchomimus*; in addition, the
holotype of *Baryonyx* possesses a hook-shaped olecranon on the ulna ...
there aren't that many apomorphies left separating the two ... but are
they different species?

  ... 'Sides, I don't need anyone to agree with me, just acknowledge and
practice science.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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