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Re: Re: pterosaurian monophyly



Thomas_R_HOLTZ@umail.umd.edu (th81) answered George's objections about
Kevin's statements on cladistics and pterosaurs:

>> But what does "better supported" mean? Victorious in synapomorphy
>> wars?
> 
> The ways the analysis can ferret this out:

..

Since I started this, I figured I should continue it; I forwarded
George's message to Kevin, and he responded:

  Mickey -- George is of course correct, and his point is frequently
  raised in systematic discussions.  A cladogram is a starting point
  for further analysis.  It is a simple tool.  It shows a pattern, but
  we know that biological patterns are the result of processes.  A
  pattern is the first step at getting at what processes we might
  usefully examine next.  There are indeed some instances in which 32
  characters are placed against 50 in rival phylogenies, though to
  date these have mostly been molecular analyses.  In more typical
  analyses, if there is this much homoplasy, then even process
  analysis may not untangle everything.  On the other hand, if you
  don't use an explicit methodology (whether cladistic or something
  that will ultimately replace it), it makes it even more difficult
  for others to evaluate your results.  (It's like the old saw: if you
  think education is expensive, try ignorance.)
  
  Obviously George is not arguing against methodology, but only
  pointing out its limits and asking, what next?  Analysis of
  competing phylogenies can be done in several ways.  You can see
  where the character conflicts are -- what data sets are particularly
  prone to conflicting signals?  If molecular, do other molecules give
  similar or different results?  If morphological, are these dental,
  cranial, or postcranial?  Do they involve certain functional or
  adaptive complexes that might result in rampant parallelism?  Do
  non-functional characters give a more consistent signal?  Do we know
  anything about stratigraphic or geographic separation that might
  make it extremely unlikely that a given character was synapomorphic
  in two forms?  None of these approaches may settle a question, but
  historical sciences (and as a rule, those that use induction)
  generally rely on what Whewell called consilience: that is, the most
  robust hypothesis is the one supported by the most lines of
  independent evidence.  Again, cladograms are simple tools, too
  simple to encompass this kind of complex historical analysis.  It is
  already clear that several major questions in dinosaurian phylogeny
  are dependent on more complex process analyses that have been done
  so far.  These include the questions of the relationships of
  marginocephalians to other ornithischians, whether hadrosaurs are
  diphyletic, and whether certain Triassic Argentinian forms are
  theropods or even dinosaurs.
  
  Please feel free to transmit the above (or part of it) to the
  dinolist. -- kp

-- 
Mickey Rowe     (rowe@lepomis.psych.upenn.edu)