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Re: Therizinosauroid apomorphies

Jack Conrad wrote-

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

I don't trust most of Sereno's characters he uses, especially in the paper
in question.  They are mostly either incorrect, or possibly correct but so
obscure that it would require a first hand examination of material to
verify, which makes them useless to people like me who have no access to
such materials.  He also conveniantly leaves out characters that would argue
against his phylogeny.  For instance, notice that virtually none of the
proposed therizinosaur-oviraptorosaur characters were used in his analysis?
How surprising that therizinosaurs grouped with ornithomimosaurs instead.
Same thing could be said of his lack of alvarezsaur+bird synapomorphies.

> 1. Subnarial foramen absent.

Note that Clark et al. say, regarding Erlikosaurus, "the presence of a
subnarial foramen ... cannot be determined".  Oviraptorids, Archaeopteryx
and Confuciusornis also lack this, and I'm unsure as to the condition in
troodontids and alvarezsaurids.

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

This character is just screwed up.  I measured this ratio for a variety of
coelurosaurs and it seems to mean nothing.

> 3. Antorbital fossa, form of ventral margin invaginated.

I can't comment as to it's accuracy, as it would either need to be
conveniently described in a paper, or I would need first hand observation.
Chirostenotes is supposed to have this feature as well though.

> 4. Nasal anteroventral process absent (1).

Although not figured, Erlikosaurus is described as having an anteroventral
process by Clark et al. Also, the process in ornithomimids is not really
absent, but very short and obtuse, which seems to also be the case in

> 5. Surangular ridge dorsal to posterior surangular foramen absent.

As far as I can tell, ornithomimids do have this ridge (just check out the
figure of the skull in the original description of Struthiomimus).  On the
other hand, Erlikosaurus appears not to.  The same with Archaeopteryx and
other birds.  Tyrannosaurs, oviraptorosaurs, dromaeosaurs and possibly
Ornitholestes do have this ridge, but it's presence in groups not mentioned
is uncertain.

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

If only I had theropod manual phalanges to experiment with...

In short, there are far more characters argueing for a
therizinosaur-oviraptorosaur relationship than for a
therizinosaur-ornithomimid relationship.

Mickey Mortimer.