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Re: Ah ha! That's where therizinosaurs came from



Jason Brougham <jaseb@amnh.org> wrote:

> There are reasonable arguments for why and how those characters evolved, and 
> whether they are satisfactory or not is a matter of opinion.


Yes, this is true.  That's why the sequence of character acquisition
(or loss) posited by a cladogram should be paramount.  Note that, for
most "avian" flight-related characters (i.e. those absorbed by birds
into the modern flight apparatus), the order remains pretty much the
same irrespective of whether _Archaeopteryx_ is closer to dromaeosaurs
or to modern Aves.


> In one hypothesis, we actually see the characters in question in the process 
> of being assembled on the lineage leading UP to flying birds, not DOWN from 
> flying birds. That is a perfectly plausible
> hypothesis that, like the BCF one, can be tested and supported or falsified.


Just a clarification.... BCF ("Birds Came First") is an idea
promulgated by a certain George Olshevsky, an amateur
"dinosaurologist".  BCF proposes that ALL dinosaurs (even
sauropodomorphs and ornithischians) evolved from small arboreal
'dino-birds', with the various theropod lineages evolving from
'dino-birds' that were not only arboreal but flighted as well.  For
example, under the BCF 'paradigm' the tiny didactyl forelimbs of
tyrannosaurids were suggested to have evolved from large, didactyl
wings that were used by flying proto-tyrannosaurids.


http://scienceblogs.com/tetrapodzoology/2009/06/birds_come_first_hypothesis.php


(Darren is highly critical of BCF, and rightly so.  BCF doesn't get
much airtime these days, and should probably be allowed to disappear
into the ether.)


GSP's ideas about bird/theropod evolution (let's call it the
"neoflightless hypothesis") are more restrained than BCF, with only
highly derived theropods (approximating clade Maniraptora) proposed to
have possessed flight adaptations.  BCF is the "neoflightless
hypothesis" on crack.





Cheers

Tim