re: Diapsids

[David Peters <davidrpeters@earthlink.net>]

DM wrote:

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

I've heard the opposite, especially with regard to sphenacodonts to
pre-mammals. That is, the lower jaw conducts sound, especially when it
is on the ground, as it often is in reptiles, and the stapes, while
structural, also transmits low frequency vibes to the ear nerves,
wherever they may be. In that way nearby footfalls may be 'heard'.

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.
I also note that a slender independent stapes is found in Procolophon.
Champsosaurus has a short, thick, robust stapes. There is no stapes
figured for Proterosuchus, just a lot of fusion where it should be. Not
seeing a stapes figured for all of the primitive archosauromorphs.
Perhaps it is so fragile that is rarely is found. Petrolacosaurus has a
robust stapes, so that cannot be the basal diapsid according to your
homologies. Can you show me the most primitive archosauromorph with a
slender stapes so we have a starting point? 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. 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.


<<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.



<<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.


<< 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.

DP
StL