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RE: crocodile reversed or normal




Tracy,
Since _Ornithosuchus_ is the type genus, there is no question that it belongs in Family Ornithosuchidae, and I think everyone here would agree that Riojasuchus belongs in the same family.
And everyone agrees that Family Ornithosuchidae is a member of clade Archosauria, but the confusion has been in which archosaur subclade it belongs. In the 1980's it was placed in the subclade Ornithosuchia, and there was no confusion. But in the 1990's, Sereno discovered that it really belongs in Pseudosuchia. Unfortunately Ornithosuchia was not cladistically anchored on genus _Ornithosuchus_, so cladists have the confusing situation of Family Ornithosuchidae placed in Pseudosuchia instead of Ornithosuchia. This used to confuse me, it seems to have confused you, and it will continue to confuse others until the cladists get their PT taxonomy straightened out (I wish them luck, they're gonna need it, and they know my views on the inherent instability of PT taxonomy).
Although I use cladistic analysis, I am not a strict cladist when it comes to taxonomy. I prefer an updated traditional approach, and I classify Family Ornithosuchidae as a member of the reptile Order Thecodontiformes (emended form of "Thecodontia"), a large group of ancestral archosauromorphs which gave rise to Orders Crocodyliformes, Pterosauriformes, Ornithischiformes, and Saurischiformes (thence to birds).
If you want to see my classification of Thecodontiformes, you can see it in the archives of this group (posted in June, I think?), or just send me an e-mail requesting it, and I can e-mail it to you privately. Otherwise you are stuck with a pure cladistic classification ("cladification" to use Ernst Mayr's term) with Family Ornithosuchidae as member of Pseudosuchia (Archosauria, Archosauromorpha, Sauria, Diapsida, Eureptilia---just to mention some of the more inclusive clades).
Hope this helps, Ken Kinman
*********************************************************


From: "Tracy Ford" <tlford@ix.netcom.com>
Reply-To: tlford@ix.netcom.com
To: "Dinonet" <dinosaur@usc.edu>, <kinman@hotmail.com>
Subject: RE: crocodile reversed or normal
Date: Wed, 23 Aug 2000 02:35:17 -0700>

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of Ken
Kinman
Sent: Tuesday, August 22, 2000 12:21 PM
To: dinosaur@usc.edu
Subject: Re: crocodile reversed or normal



I'll take a stab at this:
I think you may be confusing Family Ornithosuchidae with the clade
Ornithosuchia. Due to some quirky cladistic anchoring, Ornithosuchidae is
now included in Pseudosuchia (not in sister clade Ornithosuchia). For this
reason I prefer using the term Ornithodira (which I believe still contains
the same groups as Ornithosuchia).
Anyway, dinosaurs have croc-reversed ankles (as do all other
Ornithodira). I believe that some of the primitive pseudosuchians (sensu
Gauthier) also have croc-reversed ankles (e.g., Erpetosuchidae), and you
dinosaurologists correct me if I am wrong, but I believe Family
Ornithosuchidae may also have croc-reversed ankles. If this is true (will
have to recheck on this), I'm not sure why Ornithosuchidae is included in
Crurotarsi, but could be another one of those cladistic nomenclatural
quirks.
It is all rather confusing, but the croc-normal ankles ("cross ankles")
apparently only occur in crocodylomorphs and other "advanced" Pseudosuchians
(but not the most primitive ones). And to clarify, I am talking about
Pseudosuchia sensu Gauthier (not Pseudosuchia sensu Benton, which most
people call Suchia).
Boy, I sure would hate to have to explain all this to a class of
college undergraduates. I can see them all rolling their eyes in disbelief,
and I wouldn't blame them one bit. :-)
-----Ken Kinman


Thanks. What I need to do is figure out where to put Ornithosuchus,
Riojasuchus, etc.
Tracy


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