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Re: Fwd: re: pterosaurs and dinosaurs (long)



At 10.12 03/10/02 -0700, ekaterina A <a_ekaterina@yahoo.com>
wrote:
It would be great if Renesto Silvio could commnent on
these matters

If there is to speak about my beloved small archosauromorphs, here I am.
For sake of conciseness I am not adding full references to my quotations here, but you can contact me if interested.


> Pterosaurs are derived prolacertiforms, closest to
> Cosesaurus,
> Sharovipteryx and Longisquama, with whom they share
> an antorbital
> fenestra without a fossa. They retain an elongated
> manual digit IV > III
> > II > I and a reduced or absent manual digit V.
I love the enthousiasm of my friend David, and in part I agree with him, but I would be more cautious in those assertions replacing "are" with "may be".
However, we should not consider David as completely an outsider in this context:
In "ancient" times Benton (1984?) put the pterosaurs off the Archosaurian clade in his revision of diapsid reptiles on Zool. Journ. Linn. Soc. (even if he retreated that *in the same paper* in a note added in proof). Bennet (1996) also disputed the Ornithodira in an excellent paper, pushing pterosaurs much lower in the archosaur cladogram.
In more recent times, Unwin suggested a possible link between Sharovipteryx and prolacertiforms and stated that it may be also related to basal pterosaurs.(also Tatarinov considered S. a derived prolacertiform, if I remember correctly).
On the other hand, I still have to see an antorbital fenestra in any prolacertiform I've examined, but this does not make David theory invalid, an antorbital fenestra may have developed later (or I cant' see very well).
What I really dislike is Longisquama. I respectfully disagree with David opinion in the placement of this critter within prolacertiforms. I won't discuss this here (eventually in another side, in another time), but my knowledge of this specimen is very limited. To me, it shares a lot of functional similarities (most likely convergences) with some drepanosaurids, but all may be due to similar arboreal adaptation. I am very sad that the posterior half of the body is unknown.


> Also note that the
> caudofemoral anchors are all greatly reduced
> producing an attenuated
> tail with implications for complete elimination of
> the retractor muscles
> of the femur and default replacement by the rotator
> muscles of the
> pelvis. You won't find that in dinos.

Slender prolacertiform femora lack distinct trochanters to house large caudifemoral muscles, this is right, but in prolacertiform we have a very wide tail base which become "attenuated" only after 6-8 caudal vertebra. However, In my opinion the pelvis rotation is feasible at least in smaller prolacertiforms which might have been facultative bipeds or even semi-permanent bipeds (see our babbling on this in Renesto Dalla Vecchia & Peters 2002, special issue of Senckembergiana Lethaea). This may have rendered fore-limb free in a "from the ground up" context.


 And the key
> synapomorphy of the
> little prolacertiforms is that big pedal digit V,
> which is greatly
> reduced in the other "ornithodires".

Here is where (IMHO of course) David is more than right, the resemblances (feel free to give the meaning you prefer to this word ) not only in the fifth toe but in the entire foot (tarsus included) between prolacertiforms and basal pterosaurs are more than astonishing. Fabio Dalla Vecchia and myself are working on this. I hope our work will contribute to add knowledge on this.

Ptero-hair of the type described by
> Czerkas is restricted to
> pterosaurs, as far as I know, but Cosesaurus and
> anurognathids had long
> caudal hairs, in the pattern of giraffe tails.
>
I haven't seen anurognathids first hand thus I wouldn't comment there, but, again and again, I would warn against Cosesaurus!!
Cosesaurus is almost surely a prolacertiform close to Langobardisaurus and tanystropheids, the problem is that the pattern of preservations in the Montral Alcover site is particular and it is even difficult to decide whether you are seeing the specimen in ventral or dorsal side, not to say seeing soft parts!!. A colleague of mine made extensive studies on the fishes from the same site and showed me very well the mess taht material is.
PhD student Phil Senter (sorry, I don't remember his affiliation; he had a poster at SVP) has examined thoroughly Cosesaurus and he could add more.
This doesn't invalidate David hypothesis on pterosaur origins *per se*, but I wouldn't use soft structures in Cosesaurs as a support , because (do not get offended David!) it is very difficult to interpret that fossil and to distinguish what there really is, what is a sedimentary artifact from what we hope/feel/suppose there is. Ellemberger saw FEATHERS in Cosesaurus.
It happens even in easier cases: the semilunate carpal of Megalancosaurus simply NEVER existed, and it was plain clear from the first published photo, but lots of words have been written on this NON EXISTENT character years ago. Surely I am the first who produces (lots of) misinterpretations, this is not a j'accuse, is an humble invitation to be as cautious as we can (succed to) be.


To shut up it all before you start snoring, if you point a gun to my head and ask me "your opinion or your life" I would probably (try to kill you without answering) share the team who set pterosaurs apart from dinosaurs, that is pterosaurs may have sorted from a bunch of basal archosauromorphs and perhaps prolacertiforms are among better candidates, but I for one would search for further robust evidences before putting my hand on fire for this, and would avoid questionable cases which may risk to weaken the hypothesis instead of reinforcing it. Dixit et salvavi anima mea.

Any criticism, question, feedback (insults excluded, I'm sensitive) either on the list or privately is more than welcome.
Cheers


                                                Silvio Renesto


_
The voice from the lake then asked
"which is the strangest thing of all?"
Judisthira replied
"Every day men see other men die, they see the chariots with the corpses and the fires, yet they keep living as they were immortals, this is the strangest thing of all"


                                                        (from  Mahabharatha)

Silvio Renesto

Dipartimento di Scienze della Terra
Università degli Studi di Milano
Via Mangiagalli 34
I 20133 Milano
Italy
phone +39-02-50315511
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e-mail:  renesto@mailserver.unimi.it
        Silvio.Renesto@unimi.it
have a look at our Triassic  website at
http://users.unimi.it/vertpal/index.htm