Re: Philosophies for Character Ordering

["Jaime A. Headden" <qilongia@yahoo.com>]

Mickey Mortimer (Mickey_Mortimer111@msn.com) wrote:

<I have a few problems with this.  First, leaving it unordered would make
intermediate states their own derived state.  So seven-sacraled
confuciusornithids and Protopteryx would be inclined to make a clade
separate from eight-sacraled ornithothoracines.  It doesn't make much
sense in my mind.>

  Intermediate states are already their own state. Given a matrix where
all characters are of equal weight, and previous states in a
transformation sequence don't tally-total up the numbers for a particular
character, as in an 8-sacralled animal having a "better" number if it
gained the two extra vertebrae over a 6-sacralled one sequentially (went
through a 6, then 7-sacral state), than if a second animal gained it's two
extra sacrals in one event. A matrix should already be able to treat
*Protopteryx* and Confuciusornithidae as sistergroups given enough
synapomorphies in an unweighted system. Just as the avian looking basal
dromaeosaurids would seem to make a clade based on shared features that,
rather, could easily be step-wise sequence transformation towards the
larger, more terrestrial dromaeosaurids, yet their similarities would be
prone to group them together exclusive of other dromaeosaurids, in many
observations (as in, say, Paul [2001]); similarly, this would seem to
group toothed ornithomimids from non-toothed, crested oviraptorids from
non-crested, non-wrinkle-toothed carnosaurs from wrinkle-toothed ones,
ceratosaurs into neoceratosaurs and coelophysoids, or support
coelophysoides as a clade exclusive of a more step-wise, Hennigian
arrangement with dilophosaurs closer to tetanurans than coelophysids.
Speaking only using theropods. A better non-theropod example would be the
issue with what features really do diagnose a "Iguanodontidae," and how
iguanodontid-like one has to be before it stops being hadrosaur-like; or
*Minmi* being an ankylosaurid, or ankylosauroid, or whatever; or how many
titanosaurid/-oid/-ian features will make it stop being a basal
camarasauromorphan or titantosauriform.

<This makes more sense, but I'm confused by an aspect of it.  Say the
character is "antorbital fenestra size".  Wilson would say, the pneumatic
diverticulum that occupies the fenestra could halt its growth during
development, so it should be treated as an easy loss character.  But
structures usually grow in concert with another structure shrinking. When
the diverticulum enlarges, the surrounding bone shrinks.  So why not treat
the bone growth as easy loss instead of the diverticulum growth?  Instead,
the bone growth is effectively "easy gain", which no developmental
philosophy supports.>

  Easy to do if one includes the clause that the two be the same relative
condition. However, even as diverticulum growth increses, bone should not
immediately be seen to "shrink," only it's relative size decrease. The
bone, if it stops growing, and the antorbital fossa increases in area,
would still be the same size, as in the aperture of the antorbital
fenestra. Or diplodocoid vertebral pleurocoels, in which case the
pneumatic diverticula would be present early in life, and the bone grows
around the diverticula, creating smooth-surfaced chambers and rounded rims
to any aperture or lamina dividing diverticula.

  I think Wilson's ideas have a lot to say for themselves, especially in
regards to shape ideas about unordered states, whereas sequential ordering
of phalangeal count or vertebral count must follow the observed trends
that presacral counts, sacral counts, and arragement or distribution of
transverse processes and their ribs' shapes being indicators of these
numbers, in archosaurs at least. Pneumatic characters _should_ be expected
to be more plastic than numbers, as in pleurocoel shapes, aperture size,
ornamentation of the bone in response to pleurocoels, cranial crests,
shapes of crests that support muscles or contact other bones, as these
will immediately be counted as "functional" and highly susceptible to
transformation and convergence; shape of the deltopectoral crest is an
example, or lachrymal "horns." One starts finding patterns based on the
other characters, and allows these characters to either be discarded for
lack of utility, or retained because they have a qualitative aspect in the
study.

  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.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


        
                
__________________________________
Do you Yahoo!?
Yahoo! Domains ? Claim yours for only $14.70/year
http://smallbusiness.promotions.yahoo.com/offer