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Re: More on Argentavis



> The basal part of the neornithean tree seems
> especially prone to both loss 
> of flight and impressive increases in body size; as
> well as ratites, we also 
> have dromornithids and gastornithids (both regarded
> as galloanseraeans, or 
> at least basal neognaths).

Gastornithids are Neognathae incertae sedis; not
higher landbirds (but more due to dating than to
anything else), but that's all that can be agreed upon
now I think. (Anyone know of any good post-2000 refs?)

In any case, not quite. Flight capabilities of
galliforms for example are not too well-developed, but
also very rarely lost (not quite as rarely as in
passeriforms, but far more rarely than in the usually
well-flying Anseriformes). Altogether, there is some
slight decrease in evolving flightlessness in "higher
landbirds" + passeriforms. But still, flightlessness
is so highly apomorphic that many factors weigh in far
more heavily than phylogeny, and that each flightless
lineage must probably be regarded in its own right. In
the non-Neoaves alone, there are the 3 basic ways of
becoming flightless (neoteny, size increase, and
random fluctuation as most splendidly illustrated by
Hawaiian _Branta_). If you figure habitat in (e.g.
discount penguins, plotopterids, ...), the slight
decrease beyond "higher waterbirds" would probably
become meaningless.

Giant size on continents, yes. That's probably a
matter of "the early bird...", catching the ground bus
before the mammals hopped on in force.


Eike




        
                
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