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Re: what's wrong with Jouve's Ctenochasma?



Formatted by hand -- I hope I didn't misattribute any quotes...

> > What mysterious nasal fenestra? Jouve always talks of a "nasoantorbital
> > [sic] fenestra", and it's in the expected position. But what, if
> > anything, is a "lacrimal fenestra"? The lacrimal duct???
>
> Look for the ?Obc. Figure 3. In the middle of Jouve's "N."

Jouve doesn't call this a "nasal fenestra", but a "presumed olfactory bulb
cavity". Crushed and split as the specimen is, I'm not sure if it is a
fenestra as you think.

Now what would a lacrimal fenestra be?

> > > Some other labeling errors:
> > > Fig. 1: The "prefrontal" is a part of the nasal.
> > > The real prefrontal is over the orbit.
> >
> > Probable... from my dinosaurocentric point of view.
>
> Time to come back to pterosaurs, David.

For me that's not "back"... But I don't quite understand your comment
anyway. I said you were probably right as far as I could judge that.

> > > Fig. 2: The right quadratojugal is the postorbital process of the
> > > jugal.
> >
> > I'd say... judging from its position, if it isn't a quadratojugal, then
> > it's a quadrate. A postorbital process of what ought to be the jugal,
> > and is labeled as such, is present above the qj.

Sorry! I agree with you -- unless the qj has diagenetically shifted. This
would explain why there seem to be two different ascending processes instead
of just one... which actually looks more like a result of breakage. OK.
You're most probably right here.

> > > The post orbital is too low in the tracing.
> > > The actual PO is just above it.
> >
> > No. Look where the two temporal fenestrae are.
>
> Go back to the photo.

In the photo in fig. 2 there are 2 matrix-filled areas in the back of the
skull. Judging from their positions, I think they are the upper and lower
temporal fenestrae -- and this is how Jouve labels them. I see no reason for
another interpretation.
        (Perhaps you overlooked the caudoventral border of the lower
temporal fenestra? It's only preserved as an impression of the quadrate.)
        The bar between the temporal fenestrae is composed of the
postorbital and the squamosal in all diapsids that have it. Therefore I
expect this condition to be present in the Saint-Dizier *Ctenochasma*. And
so does Jouve. The topological relations of the surrounding bones that
result fit this interpretation.

> > > Fig. 4. The "brain" in the Saint-Dizier specimen is much too small.
> >
> > Why do you simply state this as a matter of fact, even though Jouve
> > makes quite clear why he disagrees? Why should the brain,
> > for example, keep the
> > same relative size as in the baby called "*Pterodactylus elegans*" (Fig.
> > 4B)? Why shouldn't it be as small as in *Tapejara* and *Pteranodon*?
>
> Now you've lost me. Because Tapejara and Pteranodon are way off on
> another branch, while P. elegans is a sister taxon.

You know that relative brain size is size-related, don't you? Regardless of
whether it's a baby or not, "*P. elegans*" is _expected_ to have a
relatively _much_ bigger brain than the much bigger specimen of
*Ctenochasma*!

I'm sure you know that there are small New World monkeys as well as small
lemurs whose brains are twice the relative size of yours.

> Interesting that
> Jouve's talks about Tapejara and Pteranodon without showing these key
> (for his argument) taxa? Why? Because the drawings weren't available,
> judging by what was used.

He cites Kellner 1996 and Bennett 2001 on p. 546. Why should he have copied
their illustrations? Haven't they got some?

> > > Fig. 9. Jouve points to the uneven ventral margin of the dentary in a
> > > specimen labeled, Pterodactylus "kochi" B St 1878 VI 1 [No. 13 of
> > > Wellnhofer 1970] as an example of a fossilization artifact, but it is
> > > not. Instead this character is a genuine feature and the genesis of
> > > the deep mandible found in some Nyctosaurus and Pteranodon.
> >
> > Why do you simply state this as a matter of fact, even though Jouve
> > gives a
> > quite plausible explanation for why he thinks it's just squished?
>
> You have the cladistic analysis. Use it.

That's among the first things I'll do now that 2 exams are over. However,
the analysis won't tell me if any feature is genuine, a diagenetic artifact,
a typo or _anything_. Cladistics is inherently incapable of telling us that,
as I'm sure you know -- what have I misunderstood?

> > What have you done to its vertebral column? -- Other than that, it looks
> > juvenile. Short neck, short snout and all.
>
> You have the cladistic analysis. Use it.

How could it tell me if your reconstructions are correct?

> > When looking for No. 4, I learned that this is the holotype of *P.
> > antiquus*... and found this
> > http://www.pterosaurinfo.com/p_antiquus_rostrum.html. It is dead obvious
> >
> > that the multiple nares are neurovascular foramina and/or breakages --
> > that's why they look so irregular.
>
> And that's why the nasal and jugal border them both?

:-o :-o :-o Jugal? A jugal taking part in the tip of the snout?

> And they are
> present in every taxon higher than Scaphognathus?

If they are neurovascular foramina, they may well be diagnostic of some
clade. If they're breakages, it's because you paid special attention to
them.

> > > C. porocristata or porocristatum will turn out to be closer to
> > > Huanhepterus and the azhdarchids in a paper coming soon. So it is
> > > unrelated to Ctenochasma.
> >
> > Then why is its skull absolutely identical to those of other *C.
> > elegans*, apart from ontogenetic features?
>
> Show me what you mean by "absolutely identical."

Jouve has written it all.

> For my argument you'll note many differences at pterosaurinfo.com.

Where exactly? http://www.pterosaurinfo.com/ctenochasma.html doesn't help.

> > This looks possible, although it's just a splitter vs lumper problem at
> > the moment.
>
> So start lumping or splitting  -- if you dare.

I dare. But I won't do it nevertheless. You see, I don't have a
genericometer. I prefer waiting for January 1, 200n (probably n = 6).