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Re: Therizinosauroid apomorphies



Jack Conrad wrote-

> I hope that I don't come across as obtuse or as one holding out beyond the
> point of reason, but I don't see it as that obvious.  I feel that
> _Therizinosaurus_ may belong with _Harpymimus_ based on the morphology of
> the humerus and the manual uguals.

Exactly what synapomorphies do you see as uniting the two?  They seem fairly
dissimilar to me, with Therizinosaurus having a broader distal humerus (like
segnosaurs) and more distally placed deltopectoral crest and proximally
placed flexor tubercles on manual unguals.  The foot is especially
dissimilar.  Have you ever seen the foot and ankle of Therizinosaurus?  I'll
send you a picture if you want- contact me offlist.  It is very
segnosaur-like with a laterally curved ascending process, reduced
astragalus, broad metatarsus and unreduced metatarsal I.  I have heard that
some people have doubts as to the ornithomimosaur affinity of Harpymimus
though, and the ilium has the tall preacetabular process and probably the
narrow pubic peduncle of therizinosaurs...

The semi-lunate in _Alxassaurus_ is
> incompletely fused and this may or may not mean something.

The same seems to be true of Therizinosaurus and Coelurus, I think.  In my
cladograms these appears as reversals.  Alxasaurus has tons of
therizinosaur/segnosaur synapomorphies as listed in it's description.

> The D-shaped nareal bar is at least one character to unite them with
> ornithomimosaurs and a coracoid tubercle may be a trait to unite
> _Alxasaurus_ with that group.  Overall, _Beipaiosaurus_ and _Alxasaurus_
> seem maniraptoran, though.

D-shaped narial bar? The coracoid tubercle is primitive for coelurosaurs,
being present in Nedcolbertia, Scipionyx and maniraptorans (including
Alxasaurus, Beipiaosaurus, Segnosaurus and Therizinosaurus).  Most people
group therizinosaurs with oviraptorosaurs, although Sereno thinks they are
related to ornithomimosaurs.

Mickey Mortimer