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RE: Ornithomimosauria

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Rob Gay
> Hello again everyone. Once again, I have more questions, and sadly few
> answers...here it goes...
> Where did the Ornithomimosauria come from? Once again, using my
> trusty copy
> of The Dinosauria,

Okay, first off: The Dinosauria was good for its time (written in the late
1980s), but there has been considerable advances in dinosaurian phylogeny
research since then.  Among other things, "Carnosauria" as used in The
Dinosauria is polyphyletic: it includes species now considered basal
tetanurines and the maniraptoriform (probably) coelurosaurian (definitely)
tyrannosaurids as well as true carnosaurs.

>it lists it branching off from Tetanurae (if
> I'm reading
> this right), and being more derived (I guess would be the way to
> put that)
> than Carnosauria.

It is better to say "Ornithomimosauria shares a more recent common ancestor
with Maniraptora than either does with Carnosauria".

> In the section on Ornithomimosauria, there is another
> diagram, which shows Gallimimus being the most derived, while
> Elaphrosaurus
> is shown as the most basal. But below Elaphrosaurus is lister
> Maniraptora.

Note: _Elaphrosaurus_ is not considered an ornithomimosaur by most
paleontologists these days.  Instead, it is regarded as a ceratosaur close
to _Ceratosaurus_ and the abelisaurids.

> How does Maniraptora figure into the relationships between the
> rest of the
> Dinosauria, and where, in general, did the Ornithomimids come from
> (semi-directly, not like "Eoraptor", or "archosaurs") Thanks in advance.

Where do the ornithomimosaurs come from?  A topic near and dear to my
heart... ;-)

In any case: Within Tetanurae are various primitive forms, plus
Within Avetheropoda are the two clades Carnosauria and Coelurosauria.
Within Coelurosauria are various primitive forms, plus the
Within the Maniraptoriformes are two main branches: the Arctometatarsalia
(containing the ornithomimosaurs) and the Maniraptora (containing
oviraptorosaurs, dromaeosaurids, and birds).
(There is some debate over the positions of the other maniraptoriforms:
tyrannosaurids, troodontids, therizinosauroids, and alvarezsaurids.  All of
these have been proposed as being  either closer to ornithomimosaurs or as
members of Maniraptora).

So maniraptorans (as one branch) and ornithomimosaurs (as a second branch)
are two groups of coelurosaur descended from a common ancestor.  In terms of
its morphology, this common ancestor would probably have looked something
like _Scipionyx_.

Hope this helps.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796