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

Re: titanosaurs



George Olshevsky (Dinogeorge@aol.com) wrote:

<All this does is point out yet another deficiency of morphological
cladistic analysis. Unless you think that the wing feathers of
Archaeopteryx and Confuciusornis developed entirely independently, there
must be some kind of homology present among them. Which feathers are new
structures and which are inherited? Finding an answer to this question
could be quite an informative experience.>

  We're running in circles here. Cladistics is the _tool_, it does nothing
on its own, and work with it is very relevent to what you put into it.
This is true _for every other type of scientific methodology_ involving
theoretical work on how evolution works. Shapes of feathers have different
constraints on them than number does; similar passerines will have
differential feather count with similar morphology. Looking at galliforms,
many of which are becoming ground-bound, you see a change in feather count
and morphology, but both differ in flying forms, and chickens retain the
distinct slotted wing despite being essentially non-flying. Cladistics is
not to be confused with evolutionary scenarios, and is just _one_ way to
look at the data. Not all cladistics is about synapomorphies and first
appearances of features, you know.

  When looking at relationships of problematic taxa, that you take a suite
of features and select a few subjectively as being special, you are
therefore treating all the others as "crap" characters without evaluating.
I don't care which taxon is used, but the cladistic machine only
determines patterns among supplied data. Bagaraatan is a big animal, too,
on which to work on such distributions, as it appears to have a unique
feature thought to be apomorphic in *Allosaurus*, an antarticular, in a
jaw that have a surangular like tyrannosaurids, a dentary like
dromaeosaurids, vertebrae like mononykines with unique features seen in
carnosaurs (secondary neural spine in the caudals), maniraptoran pelvis
and hindlimbs, and so forth. *Achillobator* is a puzzle, indeed, but
*Bagaraatan* is friggin' nightmare.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com