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re: pterosaur wings and scans



Dear List Members:

David Unwin is quite correct in pointing out that my attempt to
redescribe the uropatagium of Sordes as bits and pieces of wing which
had drifted to the area is clearly wrong [Nature 372]. At the time the
study of pterosaurs was entirely new to me -- and the concept of a
uropatagium was also entirely new to everyone!  Like many others I had
trouble digesting the idea of a single piece of skin connecting one
entire hind limb to the other, decoupled from the tail.

I still have trouble with that hypothesis. And it too, will be
dismantled in a more conservative fashion this time in the upcoming
paper.

This summer has been a real eye-opener for me in Pterosaurland. Major
revisions everywhere!



David Unwin wrote: >>
So, where is the fossil evidence for a narrow
wing? Is anybody, anywhere willing or able to cite a single specimen in
support
of this idea? <<


Yes. Me. By the end of the year, I am told by the editorial staff.




regarding Messel bat wings, David Unwin wrote:

>> Tellingly, for example, they show quite
clearly that there was a uropatagium and that the cheiropatagium
attached to
the hind limbs. But, none of the fossils I have seen show what I presume
was
the true shape of the cheiropatagium. The chord, for example, is always
much
shorter than it was in real life. So, in this respect, the dead wings of
Messel
bats provide us with some important lessons regarding our understanding
of
pterosaur wings. <<


The actinofibrils in pterosaur wings, I presume, would prevent the same
kind of shrinkage you refer to in bats.



>>
Pterosaur tracks are now known from more than 30 localities ranging from
the
late Middle Triassic >>

I've not heard of these. Can you give references? I'm intrigued!



>>
Most of
these tracks appear to be made by pterodactyloids although some are
claimed to
be 'rhamphorhynchoid' tracks. All tracks found so far were made by
pterosaurs
proceeding in a quadrupedal plantigrade fashion.<<

A rereading of Mazin et al. 2001, their paper on rhamphorhynchoid tracks
from the Toulouse pterosaur conference indicates "no heel
mark?digitigrade."

>>
no trackways showing pterosaur proceeding on their hind
feet alone. <<

Correct. It's an arrow through my heart!



>> Peters (2000) has suggested that all pterosaur tracks were made by
members of the
Ctenochasmatidae.

Actually, at the time, I think I mentioned that the Purbeckopus tracks
matched those of Cycnorhamphus, which is not a ctenochasmatid. All
others known to that time, matched ctenochasmatid pedes, with digits
shorter than metatarsals.

>>
ut, since there are some clear temporal and morphological
incongruencies between some of the tracks and ctenochasmatids (e.g.,
Haenamichnus is Late Cretaceous and was made by a giant pterosaur, while

ctenochasmatids are unknown from this interval and do not appear to have

achieved more than 3-4m in wingspan) this idea seems extremely unlikely.

<<

These tracks were unknown to me at the time of that writing. Further
study (hinge-line analysis) indicates that azhdarchids were also likely
plantigrade, although it is intriguing to see that both pedes of
Zhejiangopterus were preserved with heels higher than the plane of the
toes.



>>
Purbeckopus might be
ornithocheiroid, thou!gh I really have doubts about this.<<

Only Cycnorhamphus, among known pterosaurs, has a metatarsal one ten
percent longer than metatarsal two, as in Purbeckopus. The only
ornithocheiroid pedes I know of belong to Anhanguera and Arthurdactylus,
both of which have very small gracile feet, plus their sister group, the
gallodactylids, were plantigrade, so the rest is prehistory.  On the
other hand, the pedes of germanodactylids, tapejarids, dsungaripterids,
nyctosaurs and pteranodontids are quite robust and hing line analysis
supports digitigrady in these forms.



>>
Taking all the evidence together (skeletal anatomy, wing membrane
disposition,
computer based models, the track record) there is no evidence to suggest
that
any pterosaur habitually preceded in bipedal fashion. <<

Imagine Nyctosaurus _trying_ to walk quadrupedally. The wings are _so_
large relative to everything else, that those distal metacarpals hit the
ground _beyond_ the tip of its beak. It would be like a child trying to
walk with grown-up crutches.

Again, David, you have to start creating reconstructions. And share them
if they can show that bipedalism was impossible!


>>
Might I add that Sarah Sangster, who recently finished her PhD on
Dimorphodon, also came to the same
conclusions as other recent studies on this pterosaur (e.g. Clark et al.
1998,
Unwin 1988) that it was a quadrupedal plantigrade.<<

At the time Sarah was only familiar with Clark's work which was
dismantled by my subsequent paper on hinge line analysis Peters 2000
(Ichnos 7(1): 11-41) where I showed a model of a dimorphodontid pes in a
digitigrade pose that did not violate Clark's dictum on
metatarsophalangeal line extension.



Re: Chris Bennett's reply and website:

Chris Bennett wrote:
>>  If what David has "found" is really there, then
in my opinion it will be possible to illustrate it adequately so that
others
can see it as well. <<

I have done so. It's on a CD full of layered images I sent to a few
interested parties. And Chris, you opened the CD! I'm pleased! (no irony
or sarcasm intended).

Unfortunately in your rebuttal website, all of the images I sent you
opened on my Mac-based system, but none of yours did, so I regret I can
make no comments on your rebuttal except to say [regarding my images],
"where's the color that dilineates the bone? The topographical lines
without the color are impossible to digest!"

Best wishes to all my colleagues, who have made this Pterosaur
Renaissance very exciting!

David Peters