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BIRDS



<<Having read the paper by Woodbury on spinal cord morphology - this is 
a great paper, it describes in detail _one_ character that will be of 
use to studies of avian phylogeny - BUT it is just that, ONE character - 
this on its own does not provide any tangible evidence for the 
production of an evolutionary scenario- cleary the contention that, for 
example, passerines are "primitive birds" will need to be tested within 
the context of a character analysis that contains more than just one 
character. As such, the result produce may simply be a single incidence 
of homoplasy -  

Gareth>>

(Not yet having read the paper but hopefully soon.) 

I agree that making vast phylogenies based on ONE character can be like 
walking a rickety bridge over some rapidly flowing river, but 
occasionally, when taken in account with other evidence, it can be quite 
helpful.  

Take bats for example:

In 1986, Pettigrew found that megabats (Megachiroptera) share several 
unique brain to eye nerve pathways not found in microbats 
(Microchiroptera), but found ONLY in primates.  This is the primary 
evidence for bat diphyly published thus far, but it involves a suite of 
nervous system characters that 1) are not easily developed in parallel; 
2) are found to be IDENTICAL in both megabats and primates.  There are 
numerous other characters that link megabats to primates (including 
_Cynocephalus_) and not microbats but I won't discuss them here.  

Anyway, sometimes a single character can be informative and can provide 
support for certain phylogenetic hypotheses.  Now, I can tell you that 
from what I have heard about this paper that nothing in it are really 
new hypotheses: piciform polyphyly has been suggested numerous times.  I 
think that now there is mounting evidence to suggest that the 
'Piciformes' of the classical sense is polyphyletic such as:

1)  The small number of characters linking Pici and Galbulae.
2)  The number of characters that Galbulae shares with Coraciidae but 
not with Pici.  

Another thing that must be discussed is the relations of the passerines.  
Really, it is only been tradition to place passerines at the head of 
avian cladograms, along with 'piciformes' and coraciiformes.  Really, 
the placement of the passerines in a basal position in the neornithines 
and neognaths really does not effect much; they are still close to the 
only real serious candidates for passerine ancestry: Pici.  

Increasingly, avian phylogeny of both living and fossil forms is very 
enigmatic.  Placements in avian phylogeny are less concrete now as they 
have ever been.  _Opisthocomus_ is a good example of poorly resolved 
relationships; it has been placed as a galliform, a cuculiform, a 
musophagid, a gruiform, etc., and it certainly sounds like its "perch" 
in the cuculiformes is becoming rather tenuous.  

But also, as Gareth rightly noted, a single character such as the 
nervous system of birds can develop in similiar ways so homoplasy would 
be rampant.  Things like the sehnenhalter in zygodactyl birds have 
evolved many seperate times.  If Elzanowski is to be believed, tooth 
loss in neornthines evolved twice (of course, there are many reasons not 
to believe the placement of hesperornithids in Neognathae such as the 
similiar morphologies of galliformes and tinamous).  

The ultimate question is: what characters should be used to invoke 
relationships within Aves and its possible outgroups?  The answer, thus 
far, is unknown.

Matt Troutman

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