Archosauromorph classification

["Ken Kinman" <kinman@hotmail.com>]

Dear Colleagues:
    Below is an updated version of my recent preliminary classification of 
Thecodontiformes (including markers showing the placement of their 
descendants---pterosaurs, crocodyliforms, dinosaurs and birds).  It has been 
expanded to include the parathecodonts (trilophosaurs, rhynchosaurs, and 
prolacertiforms) at the base of the classification.  Thecodontiformes and 
descendants form a clade which cladists refer to as Archosauromorpha.     
This clade is thought to be a sister group of another large clade called 
Lepidosauromorpha (incl. lizards, snakes, etc.).  An initial examination of 
dinosaur synapomorphies still convinces me that it is best to regard them as 
two separate formal orders, coded as sister groups in an "informal" clade 
(but I'm still not convinced they should be "formally" joined as a single 
order, since possible convergences in hip and hindlimbs have not been 
thoroughly evaluated).
    Admittedly some groups are "wastebaskets", and as one example, I 
dismantled the mammalian "Condylarthra" in my 1994 book (yes, even I dislike 
many paraphyletic groups, when they are no longer useful).
    However, I definitely do not think this is the case with the 
"Thecodontia", and being really tired of hearing strict cladists badmouthing 
this taxon as a worthless "wastebasket", I am here presenting a preliminary 
classification of Order Thecodontiformes down to family level.  The Kinman 
markers {{in double brackets}} show the cladistic placement of those Orders 
which have been paraphyetically removed (or anagenetically upgraded, to put 
it another way), including pterosaurs, crocodyliforms, and both orders of 
dinosaurs (thence to birds as well).
      More information about each family will be added later when the basic 
phylogeny is established.  I put Doswelliidae and Elastichosuchidae in this 
time, but their placement is extremely uncertain.
******************************************************
         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}}
****************************************************
    For those unfamiliar with the Kinman System (1994), the main cladistic 
sequence is numbered, and subsidiary sequences are lettered (8A, B, C, D, E, 
show the cladistic relationships within the Ornithodira clade).
   **It should be noted that the placement of Pterosauriformes in the 
Ornithodira clade is controversial, the major competing theory being that 
pterosaurs instead evolved from prolacertiforms (perhaps as sister group to 
Sharovipterygidae, according some workers).
     Thecodontiformes was a perfectly good holophyletic (strictly 
"monophyletic") group from the middle of the Permian to the middle of the 
Triassic, and shows a lot of diversity (about 30 families).  But at the end 
of the Triassic they were replaced by their more successful descendants 
(which we call crocodyliforms, pterosaurs, and  dinosaurs & birds).
     With all the controversy and uncertainty how these families are 
interrelated (and how they are related to their descendants), this taxon not 
only continues to serve a useful purpose, but the phylogenetic uncertainty 
(and relatively fragmentary fossil record) is such that it will remain a 
useful taxon for some time to come.  Unless, of course, one really prefers 
the uninformative and confusing type of classification which the Arizona 
Tree of Life is providing.
   Strict cladists tend to put either too much or too little information 
into their formal classifications (with a never ending proliferation of 
taxa).  A more informal and flexible coding for intermediate taxa (which are 
often controversial anyway) can pack in just as much information in a more 
stable and less confusing manner.  And it also has that added component of 
anagenetic information as well.
                        ---------Kenneth E. Kinman
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