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RE: Rauhut and Xu on Tugulusaurus and Phaedrolosaurus



Tim Williams (twilliams_alpha@hotmail.com) wrote:

<To play devil's advocate: What is wrong with establishing a taxon upon a 
single autapomorphy?  As long as a genus or species has ONE character that can
be used to distinguish it from any other genus or species, it is valid in my
book.  _Archaeopteryx_ has precious few autapomorphies (maybe only one), but it
is indisputably a valid genus.>

  I have my own ideas about *Archaeopteryx* and none of them favor the idea of
"genus" and *Archaeopteryx* in the same breath. 

<I would go further and say that, even in the apparent absence of
autapomorphies, a unique combination of characters is enough to validate a
genus or species.  For example, Rauhut recently upheld _Genyodectes_ as a valid
genus based upon the unique combination of characters displayed by the jaw
material, even though it had no autapomorphies.>

  My thoughts exactly, at least as far as *Archaeopteryx* is concerned. I feel
that there are morphological features that distinguish Archie from other
dinosaurs, not the least which, if you really wanna get technical, are the
features that are "gradient" between other non-avian avialeans, and more
derived birds; this includes the manner of the tail feathers, proportions of
its limbs, and the still rather unique struture or appearance of its skull, all
comprised on non-differentiating minutiae. All an autapomorphy NEEDS to be is a
feature not shared with sister taxa (or an ancestor or descendant, whatever
fossils those might be)....

<BTW, I enjoyed these summaries of _Tugulusaurus_ and _Xinjiangovenator_ - 
thanks Jaime.   I don't have much confidence that _Xinjiangovenator_ and
_Bagaraatan_ form a separate clade of maniraptorans.  I wonder how both
_Tugulusaurus_ and _Xinjiangovenator_ compare to _Yixianosaurus_?>

  Well, *Xinjiangovenator* cannot be compared to *Yixianosaurus* due to the
absence of overlapping material. The first manual digit of *Tugulusaurus*,
however, is comparable. The first metacarpal is much longer in *Yixianosaurus*
than it is in *Tugulusaurus*, by almost 2 to 1. There is greater curvature of
the ventral margin of the manual ungual, and the claw is more slender, in
*Yixianosaurus* than in *Tugulusaurus*, whereas *Tugulusaurus* has a deeper
ungual with a "smaller," more massive and segnosaur-like flexor tubercle than
in *Yixianosaurus*. The ungual's proximal articular facet is consequently
located more dorsally on the claw than that in *Tugulusaurus*. The
proportionate length of ungual and penultimate phalanx in *Tugulusaurus* is
0.86, while in *Yixianosaurus* this figure is 0.59, and in the latter the
penultimate phalanx is slightly arched versus a straighter phalanx in
*Tugulusaurus* with a stronger ventral proximal "lip" than in *Yixianosaurus*
(in which the proximal articular lips are about even). In my opinion,
*Tulugusaurus* does not exhibit the "maniraptoran" style manus, though the
ungual is similar to segnosaurs as noted a while back by Mickey. This seems
plesiomorphic, and the digit seems carnosaurian.

  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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