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Re: Therizinosauroid apomorphies

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.

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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