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

Re: Segnosaurs ejected from AVES

Ken Kinman (kinman@hotmail.com) wrote:

<You might even end up finding that a little eclecticism is advantageous
in the end. It might be a little uncomfortable, but often "no pain means
no gain".  Give it a chance.>

  Sure. No where do I form an hypothesis based on only one source of data.
I incorporate multiple sources of data into my hypothesis, and if the
hypothesis is sound, then this data is "strong." But if data contradicts
this hypothesis ... bye bye hypothesis, not data. I fully include multiple
sources, and in this, I satisfy the definition of eclectic. So do most on
this list, and phylogenetics is, by definition, eclectic. So I think we're
operating on two different definitions. Perhaps you mean because you use
some relationships produced in cladistic matrices and put them into a
Linnaean framework, that your system is eclectic...

<I would be interested to know how Beipiaosaurus would be coded with your
six semilunate characteristics.  It's possible that segnosaurs (sans
Beipiaosaurus) split off first, and that Beipiaosaurus then split off
between them and the rest of the "true" semilunate forms.>

  *Beipiaosaurus* has an essentially identical carpus as does
*Alxasaurus*, and it codes identically, so clades with Alxa and Theriz --
however, as I tried to point out, distribution of carpal characters
(arbitrarily decided character differences and states) do not in any way
denote phylogenetic information. Though some taxa may group together that
other analyses group that way, this only shows that the feature
distribution may be phylogenetically informative. *Ornithomimus* has a
manus that has oblate carpals, but they are fused to their respective
metacarpals ... but not to each other. This, when put through the matrix,
screwed it up to hell. There is no meaningful way to describe these carpal
distributions phylogenetically, wthout further material ... this is why
saying a "true" slc block diagnoses Aves is playing to the wrong crowd.
That's for people who think that evolution is simple, and that some taxa
who lack these features, they are in that group ... they are suddenly not
getting it, that reversals can happen -- but it screws up their perfect
little boxes and makes thousands of little unassociated plesia or whatever
a species that is not in a "family" (whatever that actually _is_, no one
will answer this, are they afraid?) is called. In one perspective, it
might actually be easier to think of all species as "plesia".

  The analysis, to me, shows that all the slc is is the profile of the
bone. It's mechanical, related to permitting the folding of the wrist more
easily. The trochlea restricts the wrist to a mediolateral plane of
movement, and extends the limitation on pronation. The size of the slc and
extent upon the wrist even further permits this swing. Fusion of the
elements only restricts the displacement of part, and permits transmission
of force from part to part more easily. But each of these features is
mechanical and seen in different groups. It can be lost. It has been lost.

<I had hoped, however, that Mickey's test last year would have impelled
some sort of resolution to segnosaur grouping and their position as next
to the other maniraptorans, but this does not seem to be the case.>

  Okay, I like a little doubt, but it seems that in some people's case it
is to form an hypothesis to which data can now be put, no matter what
contradicts it, even if it's not scientific (e.g., they don't look like
"birds" as I have decided to define them, so now I'm gonna look for
features that will support this ... here I have chosen a so-avian feature
that segnosaurs _lack_, so that will support they aren't "birds"). One
then wonders also why Maniraptora is being supplanted because Ken doesn't
like the name, so move Aves up there and define one of the features used
to diagnose Maniraptora (shape of the slc block) and call it by that name.
I see nothing scientific in these practices, sorry.

  Oh, this doesn't go to just Ken ... I note some similar practice in
others, some not on the list, so please do not consider this _ad hominem_.

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!?
Send FREE Valentine eCards with Yahoo! Greetings!