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Re: Re: the start



> U > Gary, dinosaurs belong to a group of reptiles called Archosaurs which
> U > evolved
> U > from reptiles called thecodonts during the middle/late Triassic.
> U > Archosaurs include all Dinosaurs, pterosaurs (winged reptiles), birds,
> U > and
> U > Crocodilians.  Thecondonts evolved from early Diapsid reptiles.
>
>Was dimetrodon a thecodont?

No.  Dimetrodon was a basal synapsid (the line which includes mammals) and
so is more closely related to us than it was to dinosaurs.

> What separates thecodonts from Archosaurs,besides hip structure?

Absolutely nothing [I'll make a cladist of you, if you don't watch out...]
In any case, "thecodonts" are any archosaurs which are not dinosaurs,
crocodillians, or pterosaurs.

> Have thecodonts sometimes been called "mammal-like reptiles"?  If so, why?
 
NEVER! (sorry about that, had to defend archosaurian honor...).  The
"mammal-like reptiles" are the Therapsida (a synapsid group), and are so called
because their jaw structure, among other traits, show that they are the
lineage which includes the ancestors of mammals.

> I know "dont" refers to teeth, what does "theco" refer to?

"Theco" is "socket", so thecodonts have teeth implanted in sockets.  Its a
poor name for archosaurs, however, since many groups (including synapsids)
are "thecodont".


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