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Re: tyrannosaurid ancestry, raptors and other fun things...



Ekaterina Amalitzkaya wrote-

>Has any one compared the braincase of Itemirus with that of Stokeosaurus?
>What is the evidence for Itemirus being close the root of the tyrannosaur
>tree. Are its primitive featuresthe cause for noticing some relationship
>with Tyrannosaurs?

Yes.  Chure and Madsen (1998) compared the two when they described
Stokesosaurus' braincase.  They both have well-defined pockets on the
basipterygoid, but Stokesosaurus is more derived because of the much shorter
basicranium, a nearly 180 degree angle between the occipital condyle,
basipterygoid processes and basal tubera, the flattened basal tubera, and
basisphenoideal sinus visible in occipital view.  It is also much more
pneumatic than Itemirus.  The above characters that distinguish it from
Itemirus are also the ones that have been seen as evidence of a tyrannosaur
relationship.  Oddly enough, these are developed to a greater degree in
Stokesosaurus than most tyrannosaurids, while several other characters found
in Stokesosaurus are more primitive than any tyrannosaurid.  So, quite the
opposite of your question, it's the extremely derived characters that have
suggested a tyrannosaur relationship.

Mickey Mortimer