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Re: Pterosaur relationships



Larry Febo responding to David Marjanovic wrote:
----- Original Message -----
From: "Larry Febo" <larryf@capital.net>
To: "David Marjanovic" <david.marjanovic@gmx.at>; "The Dinosaur Mailing
List" <dinosaur@usc.edu>
Sent: Thursday, September 28, 2000 6:01 AM
Subject: Re: Pterosaur relationships



    -----Original Message-----
    From: David Marjanovic <david.marjanovic@gmx.at>
    To: The Dinosaur Mailing List <dinosaur@usc.edu>
    Date: Wednesday, September 27, 2000 2:58 PM
    Subject: Pterosaur relationships


    Maybe this topic should not be discussed on this list, but the current
view of Ornithodira has become so entrenched that e. g. The Dinosauricon
includes pterosaurs. My question is: What are, to date, the arguments for
pterosaurs being close relatives of dinosaurs rather than Prolacertiformes?
    A website providing the evidence for (Prolacertiformes +
(Langobardisaurus + (Cosesaurus + (Sharovipteryx + Pterosauria)))) is
http://home.stlnet.com/~azero/Pterosaur_homepage. The evidence presented
there is quite compelling, but the usual hypothesis makes some sense (e. g.
one origin for ?bipedalism, ??digitigrady and endothermy), so I'd like to
know whether we really have to abandon it.

    Padian gives an interesting synopsis of the features relating pterosaurs
to dinosaurs, (as well as possible links to lagosuchians and scleromochlus)
in his article titled:"The Origin of Pterosaurs" (1984) Third Symposium on
Mesozoic Terrestrial Ecosystems" Wherin he states..."Like
dinosaurs,pterosaurs have unusually large skull openings. The presacral
vertebral column is regionalized into three distinct segments(cervical,
cervico-thoracic, and lumbar: see Bonepart 1975). The scapular is long,
straplike, and not distally flared; the coracoin is longer than wide. There
are at least three sacral vertebrae, and possibly four.  The femur has a
"fully off-set head"(Charig 1972)........" yada yada yada(although a short,
and interesting paper, can`t copy it all here.


To which I add:

In responce to the original question, I do not think that the only two
alternatives are dinosaurs and prolacertiforms.  The proposed sister-group
relationship of Pterosauria and Dinosauria goes back to Padian's 1984 paper
and has been supported by other analyses.  The pterosaur-prolacertiform
relationship goes back to Wild's work.  More recently, Peters has advocated
it on his web site.  Peters' site is certainly thought provoking, but all he
has is a laundry list of characters.  He does not define character states,
he does not
present a data matrix, and apparently has not done a parsimony analysis.  I
am not aware of any proper cladistic analysis that supports a close
relationship of pterosaurs and prolacertiforms.

Padian (1984) is a good paper and should be read by anyone interested in the
origin and relationships of pterosaurs; however, a lot has happened in
pterosaur research since 1984 and the paper is out of date.  In addition,
the paper lacks definitions of character states, lacks a data matrix, and
lacks a parsimony analysis.

Regarding the question of bipedalism and digitigrady, there was a workshop
on pterosaurs in 1995(?) attended by most pterosaur workers.  We did not
agree on anything other than that we thought pterosaurs were pretty neat;
however, and although there were dissentors on all issues, there was a
general concensus.  The concensus opinion was that pterosaurs were
quadrupedal with plantigrade pedes.  Of course, that does not mean that that
is correct, the majority of people can be wrong some of the time.  However,
I am not aware of any recent publications supporting a bipedal digitigrade
interpretation of pterosaurs.  Instead there have been numerous recent
papers arguing against bipedality and or digitigrady.  I have published that
some large pterodactyloids probably became bipedal (while still plantigrade)
because of their hyperelongate metacarpus, but I have also advocated
quadrupedality in most pterosaurs.  Jim Clark (et al.?) has published on the
ankle and foot of the Mexican Dimophodon[-like pterosaur].  More recently,
abundant trackway evidence has come to light or been accepted (see the work
of Mazin, Lockley et al., Unwin, and me - sorry if I left anyone out), and
the bipedal digitigrade interpretation is now completely untenable.

Regarding the regionalization of the cervico-dorsal vertebral column, I
dealt with it in my 1996 paper "The phylogenetic position of the Pterosauria
within the Archosauromorpha" (Zoological Journal of the Linnean Society,
118:261-309).  Here's what I wrote:

****** Begin quote ******

[Char.] 102.  Division of presacral vertebrae column into cervical,
cervico-dorsal, and dorsal regions.  States:  0 = absent; 1 = present.
Comments:  Padian (1984), Benton & Clark (1988), and Benton (1990) used this
character to support the Ornithodira sensu Gauthier.  Padian (1984: 164)
formulated the character as "presacral vertebral column is regionalized into
three distinct segments (cervical, cervico-thoracic, and lumbar)" and stated
that it was based on the description of Lagosuchus by Bonaparte (1975).
Bonaparte (1975: 16) had identified three regions in the presacral vertebral
column of Lagosuchus:

"1) the anterior cervicals (through the fifth vertebra) are relatively long,
somewhat tall, with spinous process low and longitudinally extended.
2) the cervico-dorsals (from the sixth through the eleventh) are relatively
short and tall, with the spine longitudinally short and directed anteriorly.
3) the dorsals (from the twelfth to the last presacral) are relatively long
and low, with spinous process longitudinally extended." [Note:  this is my
translation-SCB]

Bonaparte suggested the regionalization was related to bipedality and used
it to support a proposed relationship between Lagosuchus and the Saurischia.
If one accepts that Lagosuchus has 9 cervicals, then Bonaparte's "dorsal"
region begins with the third dorsal vertebra and can in no way be considered
to consist of "lumbar" vertebrae.  Pterosaurs do exhibit a regionalization
with cervicals, rib-bearing dorsals, and a few posterior dorsals lacking
ribs that might be termed lumbars.  However, that regionalization is not at
all comparable to the regionalization described by Bonaparte for Lagosuchus.
Thus, pterosaurs are coded 0.

****** End of quote from paper ******

In that paper I also dealt with all the other characters that have been used
to support various interpretations of pterosaur relationships.  I have heard
very little in the way of responce to that paper and I some of what I have
heard suggests that some people have not understood the paper.  Perhaps
others understand it and are ignoring it.

Perhaps if I find myself with lots of time and nothing to do [it could
happen!], I will undertake to update and extend my analysis of 1996 by
adding Peters' characters and including the necessary taxa to examine the
proposal that pterosaurs are related to prolacertiforms.

S. Christopher Bennett, Ph.D.
Asst. Prof. of Basic Sciences
College of Chiropractic
University of Bridgeport
Bridgeport, CT  06601-2449
cbennett@bridgeport.edu