Re: POLYPHYLY IN THERIZINOSAURS

["Jaime Headden" <jaemei@hotmail.com>]

<<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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