LOONS, GREBES AND CONVERGENCE

["Matthew Troutman" <m_troutman@hotmail.com>]

<<So do not assume that Matt is lightly dismissing bird/pterosaur 
similarities as "convergence". His statements to this effect are 
influenced by studies which suggest that grouping birds and pterosaurs 
together results in *MORE* "convergence.">>

Thanks.  

<<Ah, but recall that evolution happens, and subtle differences in knee 
structure are the sort of thing evolution produces, and evolution does 
not care whether it starts from one knee structure (say, the one you 
don't think is homologous) or another. So, just because things are built 
differently doesn't mean they weren't inherited from a common ancestor. 
I'll give you an example... my arm is built very differently from an 
ichthyosaur paddle... care to guess if they're homologous?>>

Did I mention its embryological?  :-)

I'm not denying that, even though my message made it seem that way.  
What I should have said was something like that the differences MAY (or 
in this case, almost certainly do) indicate that loons, grebes and 
hesperornithids are not as close as some authors have concluded.  Storer 
in the 1960s did something along these lines if I remember correctly.  
Now, this does not mean that these knee features are non-homologous, 
more analysis is needed for that, but these knees seem develop 
differently and from different bones (I believe, though I'm not sure, 
that Feduccia had a summary in his book of this issue).  

<<<and shared derived features with other birds.>>>

<<And that, friends and neighbors, is where you find your evidence...
do each (well, 2 out of 3) of these groups share more characters with 
*other*, non-swimming birds than with their aquatic pals? This is where 
you'll find your convergence, Larry. This is where you find your 
evidence, Matt (although the anatomical and behavioral stuff is good 
data).>>

There are a few problems using this example.  Current ornithilogical 
classification and phylogenetic theories find that gaviiforms are very 
close to pengiuns and procellariforms, but that the affinities of 
podicepiforms are elusive, even though they share several features 
related to swimming with gaviiforms and penguins.  Basically, though 
this is vastly understating the matter (podicepiforms do not share some 
of the gaviiform-penguin characters), ornithologists have accepted the 
features that I have sited in my previous message as evidence of 
non-relation.  This happens all the time in ornithology especially in 
the Olson-Feduccia group.  

<<<If we try to account for all convergence that happens in all our 
accepted  phylogenies, we end up with birds and mammals as 
sister-groups, [...]>>>

<<Actually, no. If we try to account for all convergences, we get a
phylogeny similar to what we have now, since that's what cladistics is
supposed to do. If we were somehow able to eliminate all homoplaisy, 
well, that would be a trick.>>

I should phrased my original statement better.  I was actually referring 
to Larry's methods of phylogenetic analysis.  No offense to Larry, but 
basically it is subjective to the person who is investigating the 
phylogeny at hand by weighing certain characters as stronger than others 
without further investigation.  Complexity in certain systems is deemed 
higher than anything else.  Any other features shared with other groups 
and indicate that convergence happens more often than thought are viewed 
as plesiomorphies.  (View Larry's dismissal a few months ago of 
croc-bird synapomorphies that outweigh his pterosaur-bird synapomorphies 
in sheer numbers and are also, based on current archosaurian 
phylogenies, convergent on maniraptoriforms including birds).  Now, 
based on this method of phylogenetic analysis, the examples in my 
original message such as a bird-mammal clade, which are based on Larry's 
method of phylogenetic interpretation, can account for convergence in 
characters that are viewed too complex to be convergent by calling other 
alternative synapomorphies plesiomorphies.  That was my point.

Matt Troutman 
m_troutman@hotmail.com

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