RE: Falcarius utahensis (was RE: Newfound Dinosaur a Transitional Creature)

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

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Amtoine Grant
>
> I thought that that was the prevailing theory for troodontids. In my
> armchair-palaeontological studies I've come to the following
> conclusion. Ornithomimids and therizinosaurids are sister groups.

This has been previously proposed by Paul Sereno, who included alvarezsaurids 
in the mix.


> I propose that troodontids branched off from the common
> troodontid/ornithomimid/therizinosaurid ancestor earlier in the
> transition to herbivory than the rest, partially explaining their tooth
> morphology and more obvious retainment of a prdatory body plan. The
> ischium of Falcarius is very troodontid-like above anything else
> besides an oviraptorid's. Therizinosaurids appear to have assumed a
> sloth-like status of being more stationary and evolved their long
> bladelike claws for defense(see Chased by Dinosaurs - Giant Claw).
> Ornithomimids, on the other hand, appear to have instead simply
> continued and even got better at high-speed retreat from predators,
> with the option to kick a would-be, rather like ostriches.

This is almost a weird sort of amalgam of Sereno's hypothesis and my (now sadly 
defunct) Bullatosauria hypothesis (in which
troodontids and ornithomimosaurids were sister taxa).

All that being said, the newly discovered troodontid material from China and 
Mongolia much more strongly supports them as
eumaniraptorans (i.e., the deinonychosaur-bird clade), and most likely in 
Deinonychosauria. And there are MANY numerous shared
derived features found in oviraptorosaurs and therizinosauroids, but nowhere 
else.

Even so, there is definitely a lot of homoplasy in this part of the tree. About 
one step or so out from my MPTs in my current matrix
(not the Dinosauria II one, but an even newer one), I get:
Therizinosauroidea
derived maniraptorans
        Oviraptorosauria
        Paraves/Eumaniraptora
                Deinonychosauria/Dromaeosauridae
                Avialae
                        Avialae classic
                        unnamed
                                Alvarezsauridae
                                Troodontidae

As opposed to
Informally named
        Oviraptorosauria
        Therizinosauroidea
Paraves
        Alvarezsauridae
        Eumaniraptora
                Deinonychosauria
                        Dromaeosauridae
                        Troodontidae
                Avialae

Take care,

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
        Mailing Address:
                Building 237, Room 1117
                College Park, MD  20742

http://www.geol.umd.edu/~tholtz/
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