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Re: dinosaur synapomorphies? (posttemporal opening)



Ken Kinman (kinman@hotmail.com) wrote:

<Anybody can take two taxa and use them to define a holophyletic clade. The 
question is whether
they should.  Clades should be named for groups that appear to have strong 
synapomorphies, and to
me "postfrontals absent" cannot be defended as strong.  A long list of weak 
characters isn't
convincing to me, especially when reversals are automatically invoked whenever 
the weak 
characters are not congruent.>

  Not true: a reversal is a shift in polarity from the derived condition to the 
plesiomorphic
condition. The loss of a feature so that the preserved state is as one would 
find in a more
primitive animal that did not acquire the advanced feature.

<Question.  If the three dinosaur "synapomorphies" not found in sauropods 
aren't reversals, and
they lie outside the Triceratops-bird defined "Dinosauria", do we then 
"educate" traditionalists
and the public that sauropods are not dinosaurs, or do we redefine Dinosauria?>

  I wouldn't see why: For one thing, you would have to demonstate that all the 
features that
connect sauropods to other dinosaurs would be an extensive case (about 15 
characters or so) of
convergence, and as Pete Buchholz suggested, this is a very implausible thing. 
There is so much
support for the inclusion that the three features must be considered reversed 
in Sauropoda until
at such a time that a comparative and refutatory analysis can be made, then 
published.

<And I still haven't gotten any good answers to which of Sereno's dinosaur 
synapomorphies are the
strongest> 

  I will have to agree with Dr. Brochu in stating that a character lacks any 
strong or weak signal
... it either is a synapomorphy, or is not. There's no middle ground.


=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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