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Re: Therizinosauroid apomorphies



Hi all,

Not going to try to stir up any more trouble, just answering two questions which I haven't been able to get to (teaching labs Tues and Wed, sorry for the delay on this).

George pointed out that ornithomimids don't have claws of the same dimensions as in _Therizinosaurus_. This is quite right. Ornithomimids do have unusually long and straight claws, though. Certainly, many of their claws would (i.e., _Harpymimus_) be longer than in other groups (as compared to the penultimate phalanges). Plus, _Beipiaosaurus_ and _Alxasaurus_ seem not to even approach the condition seen in _Therizinosaurus_. (I do have an idea, though, that the claws in the latter are specialized for feeding and might indicate that they are a very plastic feature intraspecifically.)

Additionally, which features might unite (at least some) therizinosaurs with ornithomimids? Sereno presents these characters:

1. Subnarial foramen absent.

2. Maxilla, preantorbital ramus length more than 50% of the length of antorbital fossa.

3. Antorbital fossa, form of ventral margin invaginated.

4. Nasal anteroventral process absent (1).

5. Surangular ridge dorsal to posterior surangular foramen absent.

6. Metacarpal-phalangeal joint, maximum extension 15? or less (metacarpal distal extensor pits absent), above the horizontal.

(see http://www.sciencemag.org/feature/data/1041760.shl ) for details.

You all have presented very good arguments and may well prove correct that Therizinosauria (or Segnosauria or whatever) form a monophyletic group. However, I think everyone would agree that questions should be asked (after all, Tyrannosauridae belonged in Carnosauria for DECADES before one Dr. Tom asked questions (and no, I don't put myself even in the same ballpark as Dr. Holtz)).

Best wishes,

Jack
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