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Re: Therizinosauroids (was Re: Giant Birds)



Nick wrote-

>There are some fairly striking similarities in the ischia of _Caudipteryx_
and caenagnathids, but I don't have my materials at hand right now and will
have to get back to you on that one.

Indeed, Caudipteryx does share some synapomorphies with caenagnathids that
oviraptorids lack.  These include a slender third manual digit, a centrally
located ascending process of the astragalus that does not expand laterally
and possibly a surangular fused with the articular.  These could be features
uniting Caudipteryx and oviraptorosaurs that were reversed in oviraptorids
or convergently developed in Caudipteryx and caenagnathids.

A good way to tell would be to examine Microvenator.  Assuming Caudipteryx
is an oviraptorosaur, the phylogeny would be (Caudipteryx (Microvenator
(Caenagnathidae+Oviraptoridae))), which other evidence points to.
Microvenator has a slender third digit, so a reversal in oviraptorids would
be more parsimonius.  On the other hand, Microvenator lacks the centrally
located ascending process, which would make parallel evoltion between
Caudipteryx and caenagnathids more parsimonious.  That's cladistics for you!
;)

By the way, therizinosaurs and oviraptorosaurs also have a proximodorsal lip
on the manual unguals that Caudipteryx lacks (Currie pers. comm. 1999).

Mickey Mortimer