Re: Diapsids

[David Peters <davidrpeters@earthlink.net>]

DM wrote:

<<Well, and *Youngina* doesn't have a middle ear.>>

Can you show me a skull without a stapes? I  haven't seen one yet.


<<Probably we are talking convergence here, because *Sphenodon* is a
derived lepidosauromorph and the others are derived archosauromorphs.>>

Not sure that Sphenodon has ever been shown to be derived, except in the
context of other sphenodontians. Not in regard to lizards.


         but I'm not seeing
         one in Choristodera, Tropidosuchus, Proterosuchids,
         Erythrosuchids.Sure the sq and qj are deeply emarginated, but
the
         quadrate appears to be straight to shallow, even if it leans.

<<Then maybe the emargination migrated laterally. Just guessing.>>

Maybe better to 'look up,' rather than guess. The jury never believes
advocates who say what you just said.


         And if homologous in diapsids, does the emargination follow the

         same pattern in all forms?

<< Doesn't matter -- if all can be derived from the same pattern.>>

If you say the pattern is homologous in all so-called diapsids, you
should be the one to find the ur-diapsid with this pattern. It's not
Petrolacosaurus, is it? Because Petro doesn't have that character. And
now the whole hypothesis comes tumbling down. Perhaps there is another
answer.


         - "Large retroarticular process. This is the insertion point
for the
         muscles that open the lower jaw. The retroarticular process of
         araeoscelidians, Coelurosauravus, and younginiforms is much
smaller."


         >>> This character seems to vary quite abit. I see a large
retro
         process on Youngoides RC91, but not much at all on
Erythrosuchus, for
         example.Hupehsuchus from the outgroup has a large retro
process.
         Snakes, from the ingroup, not much of one.


<< As mentioned above, all that matters is the variation around the
point in the tree that we're discussing. BTW, Ichthyopterygia and their
apparently close relative *Hupehsuchus* tend to be found inside the
ingroup lately.

There's an old phrase in paleontology we need to remember: "Is you is,
or is you isn't?"  'Tend to be found' is so ephemeral and popular and so
unscientific. Show evidence, David. Gain respect.


         But note that
         the little digger Bipes retains a pair  of large centralia.


<< Is the lateral centrale one of them? (Anyway -- deep within the
ingroup, so most likely doesn't matter.)>>

Let's just sweep away the unwanted data.



         You can
         see this process in action in Homoeosaurus.

<<Are you sure?>>

Two bones become one. Yes. Right at the node too.


         Convergent fusion also takes place in some
         outgroup sauropterygians, such as Endennasaurus.

<<Probably part of the ingroup.>>

You're waffling. Is you is or is you isn't?




         Youngina SAM K7710 also has this hook.

<<Really? *Youngina* is famous for lacking it.>>

I searched high and low for Youngina pedal data. If you have anything
like you describe, please send it.

<<Well, you have so many extant taxa in your matrix that you're bound to
get all manner of long-branch attraction unless you put, for example,
toxicoferan autapomorphies into the matrix. As a primitive example -- if
I'd put an eagle into my tiny Mesozoic bird analysis without adding any
neornithean autapomorphies, it would most probably come out as an
avisaurid, next to *Neuquenornis*, instead of clustering with the
duck.>>

Now there's a challenge. Turn your  probably (a priori decision) into a
reality by doing exactly that. Then tells us.
Remember, the term 'probably' belongs in the realm of gambling,
insurance and weather, none of which are remotely like paleontology
where we like to say -- is or isn't -- and then take the slings and
arrows with chest inflated.

David Peters
St. Louis