[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: giant birds



Kendall Clement writes, in response to Chroc Brochu
(whose smug superiority of croc-specialists over
dino-specialists is even more evidence in person than
across the internet, but whose talk at SVP was
probably the best I attended [how did a _log_ get in
there?] :)):

<If homoplasy (independent character derivation in 
Chris's words) was this rampant in evolution, we'd
never get congruence between trees (of extant
organisms) based on morphological and (independent)
molecular characters. We either treat the tree as a
hypothesis of character evolution or we don't. So on
that basis, BCF is very unlikely to be supported by a
given tree.>

  I will play devil's advocate and stand here on
George's theory. What Doc Chroc is talking about is
convergence in multiple lineages; you _can_ produce a
tree wherein all supplied characters (or most, anyway)
can be convergently gained in each stem and twig. But
then, figure out how many reversals are required to do
it. The number, I believe, will boggle the mind.

  But this apparent consideration of the power of
molecular trees can be very confusing, and have
sometimes been shown to be falsifiable by other
hypotheses, even molecular ones, and molecular trees
are not always accurate, either given the methods or
the polarity of the molecules being used. Take
Whippomorpha [Hippopotamoidea + Cetacea], supported by
molecules, over the Cetacea + Mesonychia clade,
supported by morphology. The problem with molecules is
that you can only use them to figure out crown groups,
and wherever the fossils lay let them lie, especially
when they leave no immediate living relatives from
which to derived DNA to test, as in mesonychians.

  The fact is, as George has said before, BCF requires
no miracles. It requires only that there being the
precedent dinosaurian taxa having been arboreal to
aquire many of the features that led to birds. Thus,
features we term 'avian' were arrived at aeons before
Archie, and that progression to the full flight mode
in Archie et al. is only a conclusion of an animal
hitting the trees, then skies, again. Yeah, anky
scutes can most certainly be derived from the same
root origin as "dinofuzz" or "pterofuzz" or whatever,
and are analogous as some form of ossified "ankyfuzz"
(but don't ever try to pet one!). I hope I haven't
misrepresented BCF, George, but this is essentially my
understanding and take on the issue. I even touched on
possible morphological precursors to this mode
(independantly) in posts on *Marasuchus*, both in
connection to arboreality, scansoriality, and
especially in those posts with Matt Bonnan about a
month ago [the calcaneal tuber/ricochet one?].


=====
Jaime "James" A. Headden

"Come the path that leads us to our fortune."

Qilong---is temporarily out of service.
Check back soon.
__________________________________________________
Do You Yahoo!?
Bid and sell for free at http://auctions.yahoo.com