Re: Pteromimus and pterosaur origins

[Michael Habib <habib@jhmi.edu>]

>  great at. After thePAUP* tree(s) is(are) created it's time to  
>  evaluate it(them). MacClade is great at showing exceptions and  
>  mistakes in coding.

MacClade will map reversals and convergences, but this doesn't make them 
mistakes in coding.  Granted, when you map character state changes you may 
suddenly realize that you coded something absent that you know actually exists, 
but major transitions, in and of themselves, need not be errors (more on this 
below).

  
>  For instance, note that all of the sister and predecessor taxa of  
>  pterosaurs in Atanassov's phylogeny have a vestigial or absent pedal  
>  digit V. Pterosaurs don't. That's a red flag that should tell any  
>  reasonable person, evolution doesn't work that way and it's time to  
>  look for more parsimonious sister taxa. The same for manual digit IV. 

I'd slow down there for a moment - how do we make such judgements about how 
"evolution works"?  If we knew the patterns already, there wouldn't be a need 
for a cladistic analysis.  The transitions above indicate is that a given 
ancestor generated some descendents with a short digit V, and others with a 
long digit V.  That's hardly shocking, and quite plausible.  More to the point, 
when reversals, mosaics, and other bits of messiness show up in a phylogeny it 
is not a sign that the answer is wrong - it just reflects the rather stochastic 
patterns that are biology.

Look at this way: Based on the methodology you seem to be proposing above, we 
would end up forbidding apomorphies and reversals in our trees on account of 
the fact that the tree would be more parsimonious without them - which clearly 
isn't what we're trying to do with parsimony.
 
>  And there's a long list that follows. Anyone who claims that  
>  pterosaurs 'suddenly appeared' in the fossil record with no sister  
>  taxa demonstrating a gradual acquisition of characters has their  
>  blinders on. The data is freely available.

There are certainly potential sister taxa, and they show stepwise acquistion of 
some characters.  But there are also all the missing bits and reversals, etc 
that make the matter rather messy.  More to the point, no matter how confident 
you are of your sister taxon recovery, there are still a lot of apomorphic 
features in pterosauria proper.  Not the least being the powered flight 
apparatus, which is what the original reference to "sudden appearance" really 
alluded to.

Cheers,

--Mike