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Re: Archosauromorph classification & Thecodonts




Timothy,
Actually I have been asking around for opinions on whether I should include choristoderes as well, and if so, should they be placed as (1) sister group to rhynchosaurs; or (2) as sister group to rhynchosaurs plus all the rest of the thecodonts.
This is a preliminary classification, and the alphanumerics are there because they are easily changed. It's preferable to modified the alphanumeric coding, rather than having to rename clades every time the cladograms change.
And the question mark coding means incertae sedis. That's why I even coded the {{Pterosauriformes}} marker with a question mark. Sereno prefers pterosaurs near Scleromochlidae, Peters prefers them in the "prolacertiform" lineage, and I don't know where Benton wants to place them. Until I find a better spot, I'm leaving them near Scleromochlidae.
Likewise, I will leave Longisquamidae and Sharovipterygidae as incertae sedis within this order unless it shown they belong elsewhere. They appear to be archosauromorphs, and Order Thecodontiformes is ALL archosauromorphs minus their croc, dino & pterosaur descendants. It's no different than Class Reptilia being all amniotes minus their mammal and bird descendants, but being paraphyletic I guess you would call that a "trash-can" too.
But as far as "trash-cans" go, Dinosauria and a lot of other groups have had problematic groups thrown into them which were later removed. If we discarded every group that has been used as a trash-can at one time or another (making them temporarily polyphyletic), we wouldn't have many taxa left. If Thecodontiformes is now paraphyletic, it shouldn't be called a "trash-can" (which should be reserved for groups that are polyphyletic---and since I believed Condylarthra was polyphyletic, I split it into separate orders in my book).
-----Ken Kinman
P.S. When I first started using the coding, I used to draw a cladogram out in the left hand margin, but after a while the coding was all that I needed (and I can see that cladogram in my mind's eye).
Any suggestions on if and how choristoderes would fit into this classification would be appreciated.
********************************************************
From: "Timothy Williams" <twilliams_alpha@hotmail.com>
Reply-To: twilliams_alpha@hotmail.com
To: kinman@hotmail.com, dinosaur@usc.edu
Subject: Re: Archosauromorph classification & Thecodonts
Date: Wed, 21 Jun 2000 13:44:14 EDT

Ken Kinman

I don't remember if I ever posted this updated version of my thecodont
classification and discussion on this list, but here it is. It should
noted
that I plan on moving Trilophosauridae so that it branches off after the
rhynchosaurs and prolacertiform families (or perhaps between those two
groupings.

Rhynchosaurs as thecodonts? Also, I don't see the choristoderes
(champsosaurs) anywhere. Following recent studies, which determined they
were closest to rhynchosaurs, these too should be included in your
Thecodontia. You see how clumsy and impractical this definition of the
Thecodontia is? On this point, I could not express my objections any better
than Jeffrey Martz's recent post.



    And Timothy, if Longisquamidae and Sharovipterygidae don't belong in
this order, where would you place them?  If they aren't one of the many
Triassic thecodont families that went extinct, I would certainly like to
know what else they could be.

That's just it, Ken. You're using Thecodontia as a trash-can.
_Longisquama_ and _Sharovipteryx_ are being tossed into your Thecodontia,
because you can't think of anywhere else to put them. They are probably not
dinosaurs, crocodilians or pterosaurs, yet both appear to be archosaurs.
Therefore, under your system, both genera get dumped into the Thecodontia.


_Longisquama_ is best regarded as Archosauria incertae sedis, and
_Sharovipteryx_ may be a prolacertiform which may or may not be close to the
origin of pterosaurs (Benton, 1999; Unwin, Alifanov and Benton, in press).
Benton (1999) also could find no evidence that _Scleromochlus_ is close to
the origin of the Pterosauria.


With respect to the system given below... Any switches in the branching
order (such as including the Choristodera; changing the position of
_Scleromochlus_; etc) are going to play havoc with the alphanumerics used to
designate each "branch". Changes happen all the time - new taxa are
described, and existing taxa are rearranged. A nice cladogram is so much
neater, and so much more explicit.


         ORDER THECODONTIFORMES
 1  Trilophosauridae
 2  Rhynchosauridae
3A  Protorosauridae
 B  Prolacertidae
 C  Megalancosauridae
 D  Tanystropheidae
 ?  Sharovipterygidae
 ?  Longisquamidae
 4  Proterosuchidae
 5  Erythrosuchidae
 6  Proterochampsidae
 7  Euparkeriidae
 ?  Doswelliidae
 ?  Elastichosuchidae
8A  Scleromochlidae
 ?  {{Order Pterosauriformes}}**(see notes below)
 B  Lagerpetonidae
 C  Lagosuchidae
 D  {{Order Saurischiformes}} (thence to birds,
        although this is disputed by Feduccia et
        al. who apparently believe birds evolved
        from an unknown/uncertain thecodont family.
 E  {{Order Ornithischiformes}}
 9  Erpetosuchidae
 ?  Ctenosauriscidae
10  Ornithosuchidae
11  Phytosauridae
12  Prestosuchidae
13  Stagonolepididae (aetosaurs)
14  Rauisuchidae
15  Gracilisuchidae
16  Postosuchidae
17  Poposauridae
18  Sphenosuchidae
19  {{Order Crocodyliformes}}



Tim ________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com

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