Re: Darren's Last response; goodbye DML

[david peters <davidrpeters@earthlink.net>]

With regrets I (and I'm sure we) bid Darren 'adieu.' His uncanny mnemonic 
abilities as well as his insights will be missed. 

For those still reading the list: 





Darren wrote: On wing membranes I wrote?

Dave, I mentioned in my previous email the Brazilian Crato
Fm azhdarchoid I?d seen at Karlsruhe: an azhdarchoid that
(so far as I can remember) preserves a brachiopatagium
extending to the ankle. 

>>>>  Thank you, Darren, for the ID. First of all, Dino's "azhdarchoid" plots 
>>>> out strongly as a germanodactylid close to dsungaripterids in a cladogram. 
>>>> And due to disarticulation and lack of the rest of the pterosaur the wing 
>>>> membrane the stain does not necessarily represent proximal wing material. 
>>>> It could just be distal wing material. However, if we suppose that indeed 
>>>> it does represent proximal wing material then the amount of stretch 
>>>> required at full extension becomes exceedingly large. It's worth looking 
>>>> into, though.  I'll put the pasta in your name, but on hold for now.


Darren also wrote:

I don?t believe
it?s possible to glean as much data from the specimens as
you seem to be able to. Many of the details (concerning
both osteological identifications and the identification of
purported soft tissue structures) are down to your
interpretation, and having (in cases) seen the same
specimens with my own eyes, I generally do not accept your
interpretations. _Longisquama_ for example: there is no
way the specimen preserves the details you?ve reported. I
have also been influenced by Chris Bennett?s comments?.
http://www.bridgeport.edu/~cbennett/Critique.html

>>>>>>>  I agree with Darren in that eyes-only observation makes it difficult 
>>>>>>> to resolve the chaos of the fossil. That's why the tracing and 
>>>>>>> colorization of the specimen in Photoshop makes such revelation 
>>>>>>> possible. As I mentioned at my podium presentation, Terry Jones saw the 
>>>>>>> toes of Longisquama, but identified them as subdivided feather shafts. 
>>>>>>> So they are visible, just hard to identify.

Plus, after having done this to 90+ fossils, I'm learning what to look for... 
and _still_ I find new treasures I overlooked previously. In some cases, it's 
neither observation nor recognition, but persistence and cross-checking on a 
cladogram which permits the details to become revealed and validated.

----------------------
>From me earlier: What sort of ptero/lizard CoG problems are you referring
to? Perhaps we could address these issues?
----------------------

>From Darren: Unfortunately I can?t find any maths on this, but if you look
at any of the lizards that employ bipedality one gets the
impression that the relatively muscular tail provides an
effective counter-balance to the rest of the animal, and I
would think that their CoG is round about the pelvis. Snyder
(1949) comments on this. Data presented by Sarah Sangster
indicates that in basal pterosaurs (which are likely to have
had a more caudally located CoG than pterodactyloids) the
CoG is too far aft for the animal to adopt a bipedal posture
unless it was capable of digitigrady, and digitigrady in any
pterosaur cannot be reasonably supported right now. I
therefore feel the lizard analogy is flawed and needs more
work. Having said all that, I still don?t have a problem with
occasional facultative bipedality in at least some pterosaurs.


>>>>>> If lizards can do it, irrespective of the math, pterosaurs could do it 
>>>>>> because they have superior equipment (increased sacral number, 
>>>>>> anteriorly hypertrophied ilium = bigger thigh muscles). As in birds or 
>>>>>> bipedal lizards, the CoG can be easily manipulated to be either head 
>>>>>> heavy or tail heavy by moving the tail, head, femur, tibia or angle of 
>>>>>> the back. Nothing out of the ordinary is required to balance a 
>>>>>> pterosaur. And the forelimbs are always within a whisker of touching the 
>>>>>> substrate to deal with momentary lapses.



Back to Darren: On the apparent lack of response to the conclusions Dave
has published in his papers, Dave wrote?.

----------------------
The problem might be that no one has argued against
my hypotheses, either privately (in my presence) or in press.
I gave a damn good argument that, although it came out of
an unexpected an overlooked corner, it answered a lot of
questions. So I'm left wondering... (is it my breath?)
----------------------

I can assure you that your work has been the subject of a lot
of discussion behind-the-scenes. I do not think however that
your papers are going to be much cited or discussed by
other pterosaur workers though. Why? Well, let me say
again that I mean no disrespect, nor do I want to be nasty,
but the problem is that your conclusions are based on your
controversial interpretations (see above). It may be that
established pterosaur workers do not want to spend their
time refuting arguments that they regard as being based on
erroneous data. An interesting thing I have learnt in
academia (specifically, from Martill) is that workers will
often not bother to publish a refutation of another worker?s
conclusions, even if they disagree strongly: this is not
because they?re lazy, dispassionate or uninterested, but
because life is too short and they have too much of their
own research to get into print.

>>> To the last statement: Agreed. To earlier statements: Grumble 
>>> behind-the-scenes all you want, but in order to refute an argument a better 
>>> argument will have to be conceived. Or cracks will have to appear in the 
>>> prolacertiform hypothesis. Let's hear'em!  I don't think that will ever 
>>> happen, but I'm hoping it will. I'd rather know the truth than promote a 
>>> falsehood. Like Newton said about Einstein: This is science. If a better 
>>> explanation comes along it will be heard, and I want to hear it. For now, 
>>> the prolacertiform ancestry hypothesis is it. The key characters are all 
>>> easy to see. The enigmatic characters only add to the weight of evidence.


Back to Darren: Re: pterosaur ancestry, I wrote?

----------------------
yes personally I agree with you that prolacertiforms appear
to be the most likely ancestors of pterosaurs. But more data
is still needed for us to be confident about this and I note
that some pterosaur workers are still luke-warm to the idea.
----------------------

And in response Dave wrote?

----------------------
Why is this so? What's the counter-argument? What's the
better hypothesis? I'm totally in the dark on this. I _know_
it's not Scleromochlus.
----------------------

Firstly, you do not '_know_' that it's not _Scleromochlus_:
what you mean is that, so far as you tell right now,
_Scleromochlus_ is unlikely to be the closest taxon to
Pterosauria. As you know there are presently three
hypotheses of pterosaur affinity; (1) prolacertiforms [e.g.,
Peters 2000]; (2) basal archosauriforms [e.g., Bennett
1996]; and (3) ornithodires [e.g., Sereno 1991). So there are
counter-arguments to the prolacertiform school. As you
know, I personally favour prolacertiforms, but given that
some noted pterosaur workers are still, as I said, luke warm
to this idea, I still feel the need for some caution, especially
so given that I?m not a pterosaur specialist myself.


>>> My response: The two alternate hypotheses cited above preceded mine and did 
>>> not include prolacertiforms in their data, so there has been _no_ counter 
>>> argument. And both of these alternate hypotheses can be quickly dismissed 
>>> if you look at the fifth toe in each clade. So, yes, I _know_ Scleromochlus 
>>> is not on the list.


David Peters
St. Louis