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Re: POLYPHYLY IN THERIZINOSAURS
<<SNIP...my best guess is that they are the sister group to
ornithomimosaurs within the Bullatosauria because of the down-turned
dentary, similar teeth, similar mandibular complex and pneumatic
parasphenoid.>>
<I agree 100% ( or at least until I see more compelling evidence for
an oviraptorosaur link; this is in press by Elzanowski.)>
Actually, a better placement would be Arctometatarsalia _incertae sedis_
for the entire clan. They share characters with oviraptorosaurs and
Bullatosaurs, and until the taxon is named that is inclusive of those
groups but exclusive of others, this is a rather parsimonious reference,
not jumping into one subtaxa in favor of another for sake of the
bullatus, which oviraptorosaurs could have secondarily lost
[speculation, of course].
Maniraptoriformes
|_Compsognathidae
| \_Arctometatarsalia
| |_Tyrannosauria
| | |_Itemiridae
| | \_Tyrannosauroidea
| | |_Aublysodontidae
| | \_Tyrannosauridae
| \_(unnamed node)
| |..Therizinosauria [-oidea]
| \_(unnamed node)
| |_Bullatosauria
| | |_Troodontidae
| | \_Ornithomimosauria
| \_Oviraptorosauria
| \..Avimimoidea
| |_Avimimidae
| \..Alvarezsauridae
| \_Parvicursorinae
\_Maniraptora
This is basically how I define the Arctoimetatarsalia, and such
characters listed in Jack's post allow its grouping, as well as a few
other characters listed by Holtz, etc. (that means I don't know exactly
who supported the maniraptoriform nature of "segnosaurs") including the
semilunate of *Therizinosaurus* and *Alxasaurus*.
Jaime A. Headden
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