Re: Questions

["Jaime Headden" <ja_headden@qilong.8m.com>]

David Marjanovic (david.marjanovic@gmx.at) wrote:

<So you disagree with Currie (1995, JVP) who wrote that in *Dromaeosaurus*
the branches diverge immediately outside the braincase? And with all those
mentionings that *Archaeopteryx* has a single opening, too?>

  This is based more on personal observation than it is on Currie's work, or
Barsbold and Osmólska's for *Velociraptor.* As for *Archaeopteryx,* the
laterosphenoid/prootic region in the Münich specimen is incomplete as it appears
to afford a very large apse in the region where foramina II-V would diverge
between the two elements, so this is trickier to infer than most.

I wrote:

<<but there's only one foramen in ornithomimosaurs;>>

and David replied:

<Really?>

  Yes, or at least in *Gallimimus,* the laterosphenoid/prootic include two large
foramina, comprising the openings of the seventh and fifth cranial nerves; a
concensus has largely been that these foramina are exclusive per nerve, however
it seems entirely possible that the anterior of the two foramina may be the V-1
opening, and the VII and V-2--3 share a foramina, but this lacks corroboration,
as in an additional taxon that suggest it is likely. The distribution therefore
seems to offer that a divergent ophthalmic branch in the bone is one state, its
divergence within the laterosphenoid exclusively (in Norell et al./Makovicky et
al. on *Byronosaurus*, this is "separate canal for the V1" [paraphrased]) is
another, and the singular opening for the trigeminal is a third, likely the
plesiomorphic, state.

  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.

  "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)