Re: Therizinosauroid apomorphies

["Jack Conrad" <conradjack@hotmail.com>]

> From: "Timothy Williams" <twilliams_alpha@hotmail.com>
> To: conradjack@hotmail.com, dinosaur@usc.edu
> Subject: Re: Therizinosauroid apomorphies
> Date: Mon, 03 Apr 2000 16:17:00 EDT

> True, some therizinosaur characters are characteristic of sauropodomorphs 
> (e.g. foot, pelvis - especially the ilium).

> From what I can tell of _Alxasaurus_ and _Beipiaosaurus_, the ilium is not 
very like that of other therizinosauroids where the ilium is known.  In fact 
the ilium of _Beipiaosaurus_ is described as unlike that of other 
therizinosauroids by its describers.

Since
> therizinosaurs are NOT sauropodomorphs but theropods,

I've come to agree with you here, but I don't know that they form a 
monophyletic group within theropods.

> True, some other characters are characteristic of ornithischians (e.g. 
> mandible, with the lateral "shelf" and inset tooth row - suggestive of 
> "cheeks"; opisthopubic pelvis, also seen in eumaniraptorans).

Point well taken.

> There are a whole lot of good apomorphic therizinosaur characters seen in 
> the skull and postcranium of these beasties, including morphology of the 
> humerus and (as George mentioned) the distinctive, laterally-compressed, 
> scythe-like hand-claws.

The claw character isn't that great.  It seems mostly to characterize 
_Therizinosaurus_+Ornithomimoidea.

So far, though, my list has grown to at least two good diagnosing 
characters:

1.  Mandibular shelf
2.  Humerus with large internal tubercle.

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