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Tyrannosaurid Braincases



Nick Longrich and Tim Williams were talking about tyrannosaurid
braincases:

  The braincases of tyrannosaurids are not so much rostrocaudally short as
rotated rostrodorsally, with corresponding reorientation of the
laterosphenoid, etc. The basicranium is very wide and pneumatic, with a
basisphenoid fossa, but not a sulcus as in non-coelurosaurs. Troodontids
also lack a sulcus. Unlike tyrannosaurids, *Itemirus* does not have an
elevated endocranium, but appears to have one that is fairly level along
the venter of the endocranium. Despite the work of Larsson on endocranium
evolution in avetheropods (Larsson, 2001, _Mesozoic Vertebrate Life_),
coelurosaurs increase this elevation with size, but not progressive
towards birds. *Itemirus* therefore, as does the Morrison braincase, does
not require a fore-shortened braincase.

  However, a description of the basisphenoid fossa in tyrannosaurids is
wanted, to better understand it's role in theropod evolution. Bakker,
Williams and Currie, 1988, offered a preliminary discussion in their
description of the braincase of *Nanoyrannus lancensis*.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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