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Re: Diapsids

<<The stapes is there, but doesn't function in hearing >>

Sorry: it doesn't function in hearing ordinary airborne sound (hereinafter OAS). It's too massive and immobile for that. Infrasound and ground vibrations are not out of the question. After all an inner ear is always present.

Now getting back to which Lepidos and which Archos have a stapes freed
up from it structural use, and which ones do not: Everything 'north' of
Nyctiphruretus (which includes Lanthanosuchus, Owenetta, the rib
gliders, etc. seems to have lost or fused the big stapes. I also cannot
find a big stapes in Milleretta, Limnoscelis, Diadectes or Pareiasaurs.

Stapedes are often not described or illustrated because they are easily lost before fossilization (unless fused -- this seems to be common in temnospondyls) or covered by matrix (the removal of which could make the skull fall apart in some specimens) or would necessitate to take articulated skeletons apart. Big, robust stapedes have apparently been described for diadectomorphs and pareiasaurs.

I can't imagine the complete loss of the stapes. If you can't find one in a fossil, code all stapedial characters as "?".

I also note that a slender independent stapes is found in Procolophon.

Oh, yes -- procolophonoids and turtles have a stapes suitable for hearing OAS, while pareisaurs don't (Laurin & Reisz 1991 and following). I forgot the procolophonoids.

Champsosaurus has a short, thick, robust stapes.

Interesting. Do code it as having this condition -- perhaps it will turn out that champsosaurs are outside the crown-group, or perhaps they'll turn out to be a reversal like *Sphenodon*.

Petrolacosaurus has a robust stapes, so that cannot be the basal
diapsid according to your homologies.

Then you have misunderstood me. It is far away from the crown of Diapsida. It is thus expected to retain the plesiomorphic condition of a robust stapes that has a mechanical function in the skull -- and that's what you are saying, isn't it.

Can you show me the most primitive archosauromorph with a
slender stapes so we have a starting point?

No. I don't have most of the literature, and the phylogeny around the base of Archosauromorpha is a wobbly affair.

I'd like to see the pattern
and it's not as clear as you suggest it is.




        Maybe better to 'look up,' rather than guess.

<<Please do that -- I don't have time, sorry.>>

This, if not arrogance, shows that you have nothing better than a pair
of twos in your hand.

Yeah, excuse me. I'd love to have the time, but I still don't have it. The real experts -- who would, judging from what literature I've had, make the same points as I -- are not on this list.

You can always 'pass' if you don't have the data
to back up your arguments. Or 'fold'. What this shows is that you like
to argue for argument's sake, something I've suspected all along. When I
don't know anything, or enough, about a subject I just watch from the
sidelines and see what is said. Or I start digging.

Even if I were a total asshole who found it fun to tease people by randomly spraying bullets at their work, it would still be _your_ job to defend _your_ hypothesis. Just because I can't find the data to support my challenges doesn't mean these data don't exist. Anticipate grumpy peer-reviewers and preempt my challenges -- so that the peer-reviewers won't make them -- by showing that the characters I mentioned either have no phylogenetic signal or that they don't change your tree when they are included in your matrix.

<<Sorry for the misunderstanding -- I'm just saying it's homologous
within the crown-group. *Petrolacosaurus* is far outside.>>

If so, then what is the basal most crown group diapsid taxon, if not the
classic Petrolacosaurus? Let's start from there.

Ah, now I get it! You don't know what "crown-group" means! Don't worry, you're in surprisingly good company...

Take a clade, identify all its living members, and trace them back to their most recent common ancestor. This ancestor and all its descendants form the crown-group of the clade. The crown-group is itself a clade, of course, and can have a name: Neornithes is the crown-group of Dinosauromorpha, Dinosauriformes, Dinosauria, Saurischia, Eusaurischia, Theropoda, and so on, and at the same time it is its own crown-group.

--+--A
 `--+--A
    `--+--A
       `--+--A
          `--+--A
             `--X--B
                `--+--B
                   `--+--B
                      `--B

If all A are extinct and all B are extant, then organism X and all its descendants (dead or alive) comprise the crown-group of the entire pictured clade.

--+--A
 `--+--A
    `--X--B
       `--+--A
          `--+--A
             `--+--B
                `--+--B
                   `--+--B
                      `--B

Extinct clades can be part of the crown-group, as shown here. They just need to be bracketed by extant clades.

--X--B
 `--+--A
    `--+--B
       `--+--A
          `--+--A
             `--+--B
                `--+--A
                   `--+--A
                      `--A

This clade is identical (at least in known content -- depending on its definition) to its crown-group.

Everyone, including you, seems to agree that a very abbreviated version of the diapsid tree looks like this:

--+--*Petrolacosaurus*
 `--X--Archosauria
    `--Lepidosauria

All living diapsids are archosaurs or lepidosaurs; it follows that *Petrolacosaurus* is not part of the crown-group. Instead the crown-group must begin at X.

<<Could you direct me toward an illustration? (Sorry for not looking
myself -- no time.)>>

Homoeosaurus can be found in

Williston, S.W. 1925. Part I: The skeleton of reptiles. In: The
osteology of the reptiles. pp. 1-201. Harvard University Press,
Cambridge.

Romer, A. S. 1956. Osteology of the Reptiles. University of Chicago
Press, Chicago.

Thank you very much. I'll try to check these out when I get to Paris in summer. I'm sure the huge museum library has them. (My advisor has the '60s version of Romer.) Actually... the geosciences library here probably has them as well, so I could find this much earlier, but it probably doesn't have Williston.

<< If you want me to, I will code an owl (of which I happen to have a
skeleton illustration -- Feduccia 1996) this weekend, put it into my
matrix, and tell you all what comes out.>>

That would be great, for both of us. I'm learning, you're learning. Your
challenges send me back to my data  and new problems and solutions pop
up. All good. And take your time.

OK.