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RE: SV: Shaking up the bird family tree
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
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
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. ;-)
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