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Re: Patagium attachment Was: Re: Pterosaur.net



On Jan 18, 2010, at 9:05 AM, Mark Witton wrote:

> Dave, 
> 
> A quick response to your comments on my pictures:
> 
> My restoration of Darwinopterus does not show the tail incorportated
> into the uropatagia: you can see that the tail does not broaden beyond
> the posterior extent of the uropataigum as it would do if only the
> dorsal portion were visible when incorporated into the membrane.

Your explanation helped me understand the illustration. Thank you for that.

> My
> other basal pterosaurs, aside from one or two very old restorations, do
> not show the tail incorportated into the membrane, either. As for the
> posture of the legs in the Darwinopterus image, the animal is meant to
> be diving, swooping its wings back and narrowing the uropatagia to
> lessen the wing area and minimise profile drag: why not use the legs as
> extra control devices to alter the shape of the wings?

Sorry, I didn't understand the dive concept. For me a diving pterosaur, like a 
diving bird and bat, would have folded its wings posteriorly at the 
metacarpophalangeal joint. I thought Darwinopterus was raising the wingtips in 
a V shape. If it IS diving, it is overextending the elbow and the fully 
deployed and limp brachiopatagia are going to flutter like a flag on a speeding 
car IMHO.



> Bats seem to do
> it fine, so I'm sure we wouldn't see pterosaurs flapping around a set
> leg posture.

Agreed. lots of leg postures. But could they essentially touch their toes 
together AND extend the legs laterally? Was the uropatagium THAT elastic? IMHO 
no. The value of Sharovipteryx shows that fenestrasaurs extend and deploy their 
paired uropatagia by bending and extending their knees. The elasticity is only 
between the individual aktinofibrils in the membranes. 

> And what's so wrong with medial pointing fifth toes?

No one ever finds them extended like that in undisturbed specimens. Same 
problem with Bennett's interpretation of the pteroid placement: there are no 
examples in the fossil record to support that hypothesis. Just the opposite is 
the toe situation in situ: nearly always a folded digit V when undisturbed. 


> With
> the feet held in the position shown in the Darwinopterus image you only
> have to flex the toes in 90 degrees from the pedal plane and voila:
> medially pointing toes.

Indeed. You can manipulate the toes to do that, but you can't find a fossil 
that shows that.

> There may be errors in the old Anurognathus
> image you're pointing to, but the fifth pedal digit appears to be quite
> opposable in basal pterosaurs and, if the limbs of such pterosaurs are
> directed somewhat outwards during terrestrial locomotion (which,
> according to Unwin 1988 and my personal observations of basal pterosaur
> femora, they are), the toe doesn't have to wrap around the back of the
> ankle that much. 

Indeed. Sprawling femora are a hallmark of pterosaurs. But remember, Mark: 
You're talking about having a skin connection between LATERAL digits. How can a 
reptile possibly evolve such a contraption?? Where does one begin? Especially 
if the closest association between the two hind limbs are the toe tips (sans 
unguals??). Think of it. These toes used to point anteriorly on opposites sides 
of the two feet, but end up pointing medially with skin stretched between them? 
Just imagine if > I < had made such a hyptohesis-- how quickly others would 
pummel me with criticism and ridicule. 

I understand the bat calcar looks like digit V in pterosaurs, but its a heel 
bone and as such a natural extension of the posterior leg axis from which both 
the bat uropatagium and calcar develop a wee bit at a time both 
phylogenetically and ontogenetically. 

There are lots of terrestrial and arboreal reasons for pterosaurs to have such 
a strange fifth toe, which are nearly diagnostic with the variety they have. 
They're not all doing the same job. 

> 
> As for all the issues of bearing an unsplit uropatagium, I really don't
> know what you're talking about: bats seem to reproduce and pass waste
> just fine with a broad, unsplit membrane between their legs. The cloaca
> was probably located beneath the membrane to avoid self-soling and, when
> it came to reproduction, it's no problem for a the female pterosaur to
> lift her leg up so the male can slide his cloaca next to hers or,
> alternatively, for the male to posses a long penis that can help
> navigate around a contracted membrane. Bats seem to copulate in the
> traditional tetrapod fashion just fine, too: I can't see any of the
> things you've brought up as being an issue.

It becomes less of an issue when the knees are fully flexed and the femora are 
brought up even with the spine, reducing the uropatagium (in your model) in the 
vicinity of the cloaca. So, even a Leonopteryx from Avatar could still make 
babies by tucking up. 
> 
> Bottom line: the united uroapatagia of basal pterosaurs remains, in my
> view, the best supported idea because of reasons discussed at length in
> the pterosaur literature.

I hate "reasons." And so should you. Evidence should always trump "reasons." 
There was good "reason" to put the pteroid in the cup of the preaxial carpal. 
Just no evidence.

> I'm not going provide references or discuss
> this further because, frankly, it's been raised enough on the DML and in
> various other places. If you don't want to buy that evidence, fine, but
> please stop telling the rest of us that our opinions are less valid than
> yours because we don't agree with your views.

It's not a "view" I'm espousing. And I don't take it personally that you reduce 
verifiable evidence to "a view." That's okay. Mark, just send me one single 
bloody example of an unsplit uropatagium or a deep chord wing membrane and I'll 
join your movement. Surely you have one of each tucked away somewhere. 

Sorry for any perceived slights. It is key that we fix this, otherwise today's 
kids who are putting Witton tracings on their mom's refrigerators, will in the 
future by refereeing and rejecting my papers. 

:  )

David Peters