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Therizinosauroids (was Re: Giant Birds)

In a message dated 11/9/99 9:35:01 PM Pacific Standard Time, 
martin.barnett3@virgin.net (Samuel Barnett) writes:

> Firstly, what happened to those four forward facing toes?  Not even very
>  theropod-like let alone bird (By bird I mean resembling extant forms).

Maybe not, but all non-avian theropods (and even some birds, e.g. 
pelecaniforms) have four forward-facing toes.  Early therizinosauroids like 
_Beipiaosaurus_ and Jim Kirkland's new Utah form show that the first 
metatarsal did not reach the ankle in therizinosauroid ancestors.  Even in 
advanced therizinosauroids, participation in the ankle joint by the first 
metatarsal was marginal at best.

>  Secondly am I missing something?  Are we talking about Secondarily
>  flightless here as the case has been made for Dromaeosaurs and Oviraptors,
>  or just plain old flightless?  

Most workers would say primarily flightless, but a few (including Dinogeorge 
and, I think, Greg Paul) would say they are secondarily flightless.  The 
Oviraptorosauria (including _Caudipteryx_, IMO) are probably their nearest 
relatives, though ornithomimosaurs have been put forward as well (e.g. 
Buchholz, Sereno).

>  The latter I can understand, but those
>  Therizinosaur arms seem too specially adapted for a secondarily flightless
>  scenario.  

But they do retain a semilunate carpal block, albeit unfused (secondarily, I 
would guess) and a slender third finger like those of dromaeosaurs, 
oviraptorosaurs, and early birds.

>  Do we have a candidate for it's flying relative?

That's kind of a lot to ask, since we don't even know of flying outgroups to 
more obviously birdlike groups like oviraptorosaurs or dromaeosaurs!

Nick P.