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re: thoughts on Dinocephalus - and pteros
First of all, Silvio's thoughts are right on the mark, and he supports his
arguments with evidence you can visit on the web or in Switzerland.
Tim Williams wrote:
After flirting with prolacertiform affinities for a brief perioid, I think
current opinion is swinging back behind dinosauromorph affinities for the
Pterosauria. This study is Exhibit A in the case for pterosaurs as
Kellner, A.W. (2004). The ankle structure of two pterodactyloid pterosaurs from
the Santana Formation (Lower Cretaceous), Brazil. Bulletin AMNH 285: 25-35.
Kellner and I corresponded on this matter and I think (i.e. I hope) he's
repentent. He, like you all, I'm sure will remember that in cladistics you can
have ankles and dorsal fins and teeth and toes that look alike, but what you
want to make sure you do is look at the entire creature at once. Bottom line,
it's a balance between a suite of characters here and a competing suite of
characters there that an unbiased computer program looks at to determine
relationships. There are just too many "stoppers" elsewhere in the anatomy to
make the connection work.
Besides, never go with public opinion in pterosaurs. It's been off the mark for
far too long. Test. Always test. Then make up your own mind. And never go with
what someone 'thinks'. Make them show you. And it better be with a suite of
characters. And preferably a primitive taxon.
If there is an archosaur-pterosaur sister taxon out there, no one is talking
about it seriously anymore.
Ironically, in the last issue of SVP, Kevin Padian writes about Osborn's
unfulfilled life time wish to see evidence of humankind's emergence from
Central Asia, rather than Africa. I wonder how long Kevin will look for his
long-sought pre-pterosaur among the Archosauria? He shows no signs of wavering,
even without evidence.
T. Michael Kessey wrote:
I think there's a consensus that they are basal archosauromorphs. The dissent
- whether they form a natural group (synonymous with _Prolacertiformes_), or
are just a polyphyletic assemblage of non-archosauriform archosauromorphs
>>>>New work, soon to be published, will show the former is correct. At least
>>>>among the non-scrappy taxa.
- whether or not pterosaurs are part of the same group (i.e., whether or not
they are pterosauromorphs)
>>>>>>>They are. More reinforcements for Peters 2000, 2001. Same paper coming
>>>>>>>soon. Drepanosaurids are in there too, as others have indicated.
>>>>>>>Characters down to the toe phalanges are included. You can see much of
>>>>>>>this at pterosaurinfo.com.
- where, exactly, they go in non-archosauriform _Archosauromorpha_
>>>>> It's been recognized for awhile that Prolacerta and Protorosaurus are
>>>>> sister taxa. No intervening forms have been unearthed yet that I know of.
>>>>> The most obvious difference between the two taxa, each one at the base of
>>>>> a major clade, is the depth of the chevrons. As in crocs and dinos, the
>>>>> chevrons are deep in Prolacerta. That means lots of retraction from the
>>>>> caudofemoralis muscle group. It sets the stage for their style of
>>>>> locomotion. The chevrons are shallow in Protorosaurus and _most_ of
>>>>> their descendants, including macrocnemids and pterosaurs. That means less
>>>>> retraction. Like synapsids, protorosaurs moved on to another method of
>>>>> hind limb locomotion away from caudofemoral retraction.
The exceptions with the deep chevrons are the drepanosaurids, but starting with
primitive Hypuronector and Vallesaurus, it is obvious that these chevrons are
secondarily developed for display or prehension or both.