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Re: Nice example of narrow chord pterosaur wing on the 'net
On Mar 20, 2010, at 2:51 PM, David Peters wrote:
I have described no technique here. And no reconstruction. This is
You have described what you suppose the wing membrane extent was, even
though much of it is missing in the specimen - that is a
reconstruction, by definition.
There are many reasons why this could be misleading.
The term "many reasons" is way too open ended. Put your cards on the
table. Be specific.
Okay, here's some examples of potential problems:
1) The membrane may be distorted, especially if the premature
termination is a form of post-mortem tearing.
2) The arc of the patagium might continue at a consistent angle, in
which case a tangent line extrapolation would be altogether inaccurate
3) The membrane might not follow a gradual arc, but may instead have a
sharp turn or angle in it
4) The membrane as preserved may not be in its original plane, meaning
that the torn (or unprepped) edge is not oriented in the z axis in the
manner we expect.
Essentially, assuming we know where it was going just because the
little bit of edge left on the inboard side kind/sorta points at the
femur is premature. I am not going to claim that the CM specimen
shows a broad attachment; I also am not going to claim that it shows a
narrow attachment. It simply does not preserve an inboard attachment.
Are you sure you don't get a death spiral? Please, Mike, You can
avoid it only for so long... Let's talk about that line leading off
the tibia. And identical lines on the Vienna specimen.
Yes, I'm sure - a spline isn't that hard to do. My point is not that
it aims at the tibia - my point is that there are many potential
reconstructions, one of which happens to point that way. Others point
towards different solutions. I could just as easily argue that the
specimen suggests a hind limb completely free of the wing membrane.
Point is, again, that the CM specimen just doesn't have an inboard
wing, so there is little use in trying to make one up.
And, if you put the body back on the Zittel wing (see Peters 2002)
another identical situation. I'm not the only one doing this. John
Conway duplicates this here:
John also illustrates potential tibial attachments, ankle attachments,
and wings free of the hind limb altogether. He acknowledges the
uncertainty, and since he must pick a reconstruction for any given
illustration, goes with what suits for a given image. It is not meant
to imply any degree of certainty (yes, I know this is his take,
because I talk to John on a regular basis).
But I don't think you can make either argument. The membrane isn't
there, so making wild suppositions is no good here.
"The membrane" was described by Wellnhofer in 1970. I'm not the
first to see it. Or are you talking about a membrane attaching to
the tibia, no wait -- the fifth toe - that isn't there? Please be
specific or send drawings. You are adding to the confusion. We need
your finger to point to somewhere on the picture somehow.
"The membrane" in question is the inboard wing (i.e. proximal to the
elbow), which happens to be missing in the CM Pterodactylus.
Therefore, nothing to point to. I never claimed an attachment to the
tibia or fifth toe - I claim that the inboard wing is not preserved.
See above. "Does" -"does not" are closing arguments. We haven't
gotten there yet. Time to provide the charts and graphs.
Charts and graphs of what? The inboard wing is not present in the
specimen. I am not comfortable making one up, unless it is for purely
artistic reasons (in which case I don't care which version you pick).
That is honestly the extent of my argument; there is nothing to plot
on a graph.
The opposing camp has given several examples.
Wrong. NONE have been delivered. You have only >cited< examples.
Citation of peer reviewed work is an important aspect of scientific
procedure. I trust in the observations of those that have carefully
looked at the original specimens, assuming they present documentation,
unless I have looked at the same specimens in person and determined
differently. Besides, I didn't say that *I* am the opposing camp; I
merely suggested that the opposing camp has given examples, which they
You have dismissed them for various reasons, and while some of your
arguments bear merit, others can say much the same about your
narrow wing examples, leaving us eagerly awaiting a clear example
of either one.
If you don't like this wing example show what >is< happening in the
I can't tell what is happening in the fossil because it does not
preserve the detail in question. What I *can* do is run my
calculations using a variety of potential wing attachments,
constraining them according to the parts that we do have. As it turns
out, the precise nature of the inboard wing has less effect on the
results than we might expect, therefore I can make conclusions about
locomotion within known confidence limits, despite the inboard wing
Personally, I find several of the hindlimb attachment examples
Send just one of your best.
I have done so a few times, and your consistent response is to dismiss
the examples according to your digital tracings. I don't know that
your reinterpretation is wrong, but I remain skeptical because I give
greater weight to those that have seen the specimens in person. I
don't particularly mind that you have a different interpretation, but
it is a tad frustrating when you suggest no such potential examples
have ever been produced.
but even then, we do not have attachments for the vast majority of
clades, and attachment could easily vary.
If there was an alpha example and an omega example I would agree
that we could have everything inbetween. But we have only one
example over and over. Seriously, send one opposing example and I
will be on your side.
I have done so, but even putting that aside, you don't have one
example over and over - even if you are dead on, your examples still
come from only a handful of the known clades. There are no inboard
patagial extents preserved in any azhdarchids, pteranodontids,
nyctosaurids, or ornithocheirids, for example. There is a shredded
one from an azhdarchoid (potentially a tapejarid), but otherwise none
from that larger clade altogether. It doesn't matter how you
interpret everything else, that that is a lot of diversity for which
we don't have any data - therefore, the attachment could be variable
without our knowledge.
Fortunately, we have lots of good outboard wings, so we can
reconstruct that much with relative confidence. It turns out that
the specifics of the inboard wing don't make much of a difference
when you work out the numbers, because a fillet is not very
Irrelevant at this point.
Not really - we care about the wing extent largely because of the
implications for functional analysis. If the variation in potential
wing extent has little effect, then the impact of uncertainty is
reduced. This is handy.
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