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
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