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Re: Therizinosauroid apomorphies
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
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.
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