RE: synapsids (was RE: pdf request)

["Thomas R. Holtz, Jr." <tholtz@umd.edu>]

> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] 
> On Behalf Of tyazbeck@comcast.net
>
> If you visit David Peters' website, he has his own 
> mega-cladogram that apparently includes more reptile taxa 
> than any other. I believe he includes the synapsida as the 
> sister of Archosauromorpha. Could synapsids and diapsids be 
> sister taxa, a clade excluding parareptiles, or even other 
> reptiles? I don't know a lot about Paleozoic diapsids, but I 
> hope someone else does.

I will leave it for others to comment on detail, if they wish (David? Mickey?). 
But in brief, Peter's analyses have a lot to be
desired in terms of anatomical interpretation, methodological approaches, etc.

The wealth of data (genetic, genomic, morphological, developmental, etc.) 
pretty securely place turtles and traditional diapsids
together in at least some combination, and the skeletal data for parareptiles 
being closer to diapsids than to synapsids is very
strong.

The idea of a synapsid-archosaur or synapsid-diapsid clade clade has a long 
history (Diaptosauria; early non-computerized cladistic
analyses, etc.) And you can certainly pick out a few characters to support it 
(thecodonty, for one). But it doesn't pop out in the
really comprehensive studies of Permo-Triassic critters.

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA