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Re: BFC Epiphany



Andreas Johansson writes:
 > On 9/26/07, Mike Taylor <mike@indexdata.com> wrote:
 > > Put this way, it's obvious that the problem is simply one of
 > > characterisation.
 > 
 > I don't think you can dismiss it like that. First, at least in that
 > post, Olshevsky's topology is decidely unusual (monophyletic
 > Phytodinosauria, Longisquama as a basal theropod).

True, but I think that's a side issue: George's belief in a
monophyletic Phytodinosauria(*) is orthogonal to BCF: the BFC idea
smells the same whether Ornithischia and Sauropodomopha are successive
outgroups to more derived dinosaurs, or whether they together form a
single monophyletic outgroup.

(*) for those who don't know, Phytodinosauria is the name given a
hypothetical sauropodomophs-and-ornithischians clade, if it turns out
that they share a common ancestor to the exclusion of Saurischia.
AFAIK, this hypothesis is pretty much dead in the water now, and it's
perfectly possible that George has abandoned it during the twelve
years since he posted that message.

Longisquama ... uh.  Not sure what's going on here: was George saying
that it's more closely related to classic theropods than sauropods
are?  If so, I dare say he's shifted position on that idea, too.
Again, it's not close to the soul of BCF, it's just an incidental
detail of one particular BCF-compliant model.

 > Second, look at his summary of his hypothesis from a previous post
 > in that thread:
 > 
 > "The BCF thesis is that ALL dinosaurs--not just certain groups of
 > theropods--were ultimately descended from small, arboreal
 > archosaurs (which I call dino-birds), of which one lineage (which I
 > call the "central lineage") represents an adaptive sequence that
 > begins with a small, lizardlike, probably arboreal "ancestral
 > archosaur" (perhaps resembling _Mesenosaurus_) and ends with any
 > modern bird."
 > 
 > That's more than a characterization of topology: it's a scenario of
 > archosaur evolution. Whether we see Brachiosaurus brancai or Passer
 > domesticus as the end goal of archosaur evolution is a matter of
 > perspective: whether their last common ancestor was arboreal is
 > not.

OK, it's a fair cop -- I oversimplified.  Sort of.  But it's still
true that this comes down to how you optimise the character
transitions on your cladogram.  Given a matrix and a phylogeny, you
can easily reconstruct the most parsimonious basal states.  Where
George's model falls down is that the character states he advocates
are grossly unparsimonious.

(By the way, in the Brachiosaurs Came First model it's good, honest
Brachiosaurus altithorax that is the Pinnacle Of Creation, not that
smarmy arriviste B. brancai!)

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor    <mike@indexdata.com>    http://www.miketaylor.org.uk
)_v__/\  "You should never have to tell the computer something it already
         knows" -- one of the original Macintosh interface guidelines.