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Re:



>I would be grateful if anyone could get back to me at 
>sgl3gp@uk.ac.cardiff with info on what you can do on this survice.  I 
>would be particularly interested in info on the thecodonts and their 
>relationships to the early dinosaurs. Thanks G.
>

Hello there.  I hope this information helps:

If you want some up-to-date information on the animals traditionally called
"thecodonts", and have access to a library containing issues of the _Journal
of Vertebrate Paleontology_, then here are some excellent references:

Parrish, J. Michael, 1993.  Phylogeny of the Crocodylotarsi, with reference
to archosaurian and crurotarsan monophyly.  JVP 13(3):287-308.

Sereno, Paul C., 1991.  Basal Archosaurs: phylogenetic relationships and
functional implications.  JVP (Supplement to Number 4): 1-53.

Sereno, P.C., and Arcucci, Andrea B., 1994.  Dinosaurian precursors from the
Middle Triassic of Argentina:  Lagerpeton chanarensis.  JVP 13(4):385-399.

Sereno, P.C., and Arcucci, A.B., 1994.  Dinosaurian precursors from the
Middle Triassic of Argentina: Marasuchus lilloensis gen. nov.

The basic gist of these papers is that the "Thecodontia" is a paraphyletic
group (a group with a common ancestor but not all of its descendants).
Except for some primitive forms like Euparkeria, archosaurs can be divided
into two groups: Crurotarsi, which is crocodiles, phytosaurs, aetosaurs, and
other, predominantly quadrupedal archosaurs; and Ornithodira, which is
divided into Pterosauria and Dinosauromorpha.  All ornithodirans appear to
have been bipedal (at least ancestrally).  There are a few dinosauromorphs
which are not considered true dinosaurs: Lagerpeton, Marasuchus (formerly
Lagosuchus) and Psuedolagosuchus.  These are the "thecodonts" closest to
dinosaurs:  small, Middle Triassic bipedal archosaurs with an upright stance.

>

Thomas R. HOLTZ
Vertebrate Paleontologist, Dept. of Geology
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Phone:301-405-4084