Re: synapomorphies not "being" equal

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

Ken Kinman (kinman@hotmail.com) wrote:

  For one thing, synapomorphies are not created, they are observed. There _are_ 
features that
unite two forms on a morphological paradigm, these being synapomorphies. I do 
recall that you are
a neontologist and appear to be more familiar with genetic paradigms rather 
than morphological
ones. Morphology does give us a different framework to operate in.

<I've been thinking very hard about this, and I am still not convinced that all 
synapomorphies are
created equal. Some are "stronger" than others no matter how long or big the 
evolutionary gap
happens to be in which it falls.

  In my opinion, the one synapomorphy of Mammalia, the movement of the three 
ossicles from the
mandible into the ear of the first mammals, was strongly selected for and 
occurred relatively
rapidly. It is thus a very strong synapomorphy.>

  Yes, it is a significant synapomoprhy. However, there are more than one 
synapomorphy for
Mammlia, but this depends on what group you call Mammalia. If you are referring 
to all eucynodonts
with three middle ear ossicles, then this is a broad category indeed, and would 
include a good
deal of fossils (*Prokennalestes*, *Kuhneotherium*, etc..). However, as you 
note, you'd rather not
have

<This almost cries out for the need for these purported synapomorphies to be 
evaluated, and that
the strongest be identified and carefully scrutinized. The therapsid-to-mammal 
transition is just
as well documented (if not more so) as that of the transition to 
"non-dinosaurs" to dinosaurs.
Therefore the lack of a strong synapomorphy in the latter should be taken as a 
strong signal that
a comprehensive reevaluation is required. The question is who will be the "Dave 
Peters" of
dinosaur origins.>

  So far, Paul Sereno, whose work has been somewhat in part revisionary of 
dinosaur
interrelationships and (especially with Novas) the origin of Dinosauria. Novas 
has been working on
dinosaur origins after Gauthier and before Sereno was, and came to the same 
conclusions as did
Gauthier, and Bakker and Galton back in 1985 (before Gauthier's findings were 
published). Or are
you trying to find someone to realize your hypothesis of a paraphyletic 
Dinosauria?

<I believe than Crurotarsi will probably not survive, and it is still a toss-up 
whether Dinosauria
will survive as a clade. Therefore those who have challenged me to come up with 
an alternative set
of synapomorphies will have to wait for me to catch up or hope that those that 
those who need less
"catching-up" will rise to the challenge. I would prefer the latter, since I 
have other projects
that need attention, and strongly suspect that at least one of them will will 
rise to this
challenge. All I can say is the sooner the better.>

Then you enter this game with loaded dice, Ken. Saying something to the 
equivalent of "Crurotarsi
doesn't look real to me, it must be bad." This is not science.

and George Olshevsky (dinogeorge@aol.com) wrote:

<Incidentally, any clade is united not by a list of synapomorphies but only by 
a single
synapomorphy; in any list of synapomorphies, some must inevitably be 
synapomorphies of nested
groups contained in the clade, and others must be plesiomorphies of clades that 
contain it. This
is because it is extremely unlikely that a set of apomorphies would all evolve 
at exactly the same
time. Apomorphies appear in a lineage in serial order, sometimes in rapid 
succession, sometimes
more slowly. When they appear in rapid succession and the fossil record is poor 
(as usual), it
presents the illusion that they appear all at once.
For example, two apomorphies that are said to unite Ornithischia are the 
presence of a predentary
bone and the presence of an opisthopubic pelvis. One of these must have 
appeared first, but the
fossil record is too poor to tell which. Suppose the predentary appeared first. 
Then it's not a
synapomorphy of Ornithischia; it's a plesiomorphy, because there was at least 
one
non-ornithischian animal that had a predentary but not the opisthopubic pelvis. 
(Likewise if the
opisthopubic pelvis appeared first.) By definition, the only way a feature can 
be a synapomorphy
of a clade is if it appears in organisms within the clade but not outside the 
clade.>

  Wonderful way to put it, George. Perfect. I'd like to add, however, that the 
more apomoprhies
between two taxa indivates the amount of phyletic space between them on the one 
hand, and the
degree to specialization and distinctiveness of the one taxon on the other. For 
instance, both
Hadrosauridae and Ceratopsidae were, until recently, diagnosed by around 30 
features each, until
some taxa were removed, shortening the list, and one is left with a bunch of 
more closely-knit
taxa that can probably be sunk into one another. Not to step on Jon's toes, but 
I can see a few
hadrosaurid synonymies that should have been dealt with a long time ago, 
formally.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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