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Archosaur phylogeny (was Re: Thecodonts?)



>>I was hoping somebody would bring this up, but I guess it's left to me...
>>one of the earlier postings said to look at crocodilians as dinosaurs...
>>BRRRRRRP! WRONG ANSWER! Crocodilians are another group of reptiles that
>>branche
>> off from the thecodonts ran a parrallel course with the dinosaurs... it is
>>no more correct to call crocs dinosaurs than it is to call turtles dinosaurs.
>
>   Are you sure the crocs branched off from the thecodonts?  My dino class
>professor mentioned that the term "thecodont" was falling into disfavor,
>with "protodinosaur" taking its place.  I suppose its possible that crocs
>and pteros came from protodinosaurs, but it makes more sense to come from
>protodinosaur ancestors (protoprotodinosaurs?)

To use current archosaur taxonomy (sensu Gauthier, Parrish, Sereno, etc., etc.):

Archosauria is divided into two groups.  The (ironically named)
Pseudosuchia (junior synonym, Crurotarsi) contain all crocs and all
archosaurs closer to crocs than to birds.  This includes most of the
traditional "thecodonts" (aetosaurs, parasuchians, rauisuchians,
ornithosuchids, etc.).  The (even more unfortunately named) Ornithosuchia
(including the node-based taxon Ornithodira) includes birds and all
archosaurs closer to birds than to crocs.  This includes dinosaurs,
pterosaurs, and some tiny Middle Triassic forms like Lagerpeton, Lagosuchus
(?= Marasuchus), and Pseudolagosuchus.

                                
                 Thomas R. Holtz, Jr.                  Phone: 703-648-5280      
                 Vertebrate Paleontologist         Fax:    703-648-5420
tholtz@geochange.er.usgs.gov ------------>       th81@umail.umd.edu
U.S. Geological Survey          ------------->       University of Maryland
Branch of Paleontology & Stratigraphy ---->       Department of Geology
MS 970 National Center
Reston, VA  22092               ------------->        College Park, MD  20742
                                                          U.S.A.