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Re: Archosauromorph classification & Thecodonts

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
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