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>I would be grateful if anyone could get back to me at
>email@example.com 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