RE: SV: Shaking up the bird family tree

[Tim Williams <twilliams_alpha@hotmail.com>]

Tommy Tyrberg wrote:


>> The problem here is that to argue that flight is lost, you must have
>> 1) a single gaining of flight, 2) loss of flight in ostriches, 3) loss
>> of flight in rheas, and 4) loss of flight in the cassowary/kiwi/emu
>> clade. This is more steps than a simpler explanation in which tinamous
>> gained flight after the whole lost it. A tad more parsimonious, rather.
>
>
> Being parsimonious does not necessarily mean the same as being right.
> The problem here is that we know that cases of bird lineages becoming
> flightless are extremely common (I could cite a couple of hundred
> instances), while we know only "a single gaining of flight" somewhere
> back in the Jurassic.
> Using the same argument I could just as easily argue that several rail
> taxa are primitively flightless since they consist of one flighted and
> several flightless species.



Yep, I agree.  From a morphological perspective, regaining flight in birds from 
a flightless ancestor requires so many reversals that it is very 
non-parsimonious.  


In passing, this highlights a key distinction between molecular and 
morphological analyses and how they are applied to evolutionary hypotheses.  
Molecular phylogenies use genes/proteins to build phylogenies, and then make 
inferences about the distribution of morphological characters - and, further, 
what ecomorphological scenarios can explain the topology.  A morphological 
character-based analysis, on the other hand, deals with morphological 
characters directly - so the distribution of these very same characters appears 
on the tree.  


If avian morphological characters were superimposed on the molecular phylogeny 
of Hackett et al. (2008), then the point at which "secondarily flighted" 
tinamous diverge from other paleognaths would see a very high number of 
character reversals.  Such a large number of character reversals would no doubt 
be rejected by any analysis that uses morphological characters.  Thus, this 
particular topology (tinamous nested in ratites) represents an irreconcilable 
difference between what the molecules are telling is and what the morphology is 
telling us.  I don't know who is right; but I wouldn't assume that the 
molecules are (despite the high bootstrap values).


Same goes for splitting up Falconiformes into a falconid clade and a 
cathartid-accipitrid clade.

---

BTW, while there is overwhelming evidence for a "single gaining of flight" for 
birds somewhere back in Jurassic, the idea does have at least one detractor...


Kurochkin, E.N. (2006). Parallel evolution of theropod dinosaurs and birds.  
Zoologicheskii Zhurnal. 85(3): 283-297.


Not a great paper, it has to be said.  ;-)


http://dml.cmnh.org/2006Sep/msg00016.html


Cheers

Tim


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