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POLYPHYLY IN THERIZINOSAURS



Recently there was a suggestion by Jack Conrad that therizinosaurs were
polyphyletic, with the Therizinosauridae as the sister group to ornithischians
(though itself, paraphyletic) and _Alxasaurus_ being a basal oviraptorsaur.

I find this hypothesis unlikely for numerous reasons, the first of which is
that _Alxasaurus_ is clearly related to other therizinosaurs.  For instance,
the pedal structure of _Alxasaurus_ is broad and has four functional toes like
other therizinosaurs, and the teeth are very similar to those in
_Erlikosaurus_ and _Segnosaurus_, as well as bullatosaurs and parvicursorines.
The forelimb preserved in _Alxasaurus_ is also very similar to that seen in
_Therizinosaurus_ itself, so a close relationship is probable.

As for what therizinosaurs are related to, 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.

Peter Buchholz
Tetanurae@aol.com

You're messin' with big momma now!