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Re: Tyrannosaur vision

Richard W. Travsky <rtravsky@uwyo.edu> in response to my description
of how Kent Stevens mapped the visual fields of tyrannosaur eyes

> I was thinking of this from the other perspective - from the eye
> socket itself...

A) they're the same thing, 2) if they weren't then it appears to me
that your thinking is backwards -- animals see by virtue of the light
that reaches them, not because of something sent out by their eyes,
and iii) good thing for my point "A" because my memory failed me
yesterday.  There's no important difference between what Stevens
actually did and what I described yesterday, but my details were
wrong.  Starting with the most minor, it was glass, not plexi-glass.
Moving upward, he didn't shine the laser through the glass, he just
used the laser to illuminate the eye.  He looked at the sculpture with
one eye closed, and marked the glass at places where he could just see
the laser spot past the snout from various angles.  What he did was
actually more like what Rich wanted than what I described, but as I
said, the two things are the same.  Sorry about the screwed up
details; until today, it had been about five years since I'd last
looked at the Coates article...

Anyhoo, Phil Bigelow <bigelowp@juno.com> asked:

] Did Stevens also run his laser/Plexiglass test on skulls of extant
] diapsids?  To show that his light sabre technique correlates well
] with known field of views of living animals?

The article doesn't say.  As Jordan Mallon <jordan.mallon@gmail.com>
pointed out, the article mentions the fields of view of humans and
cats.  It also talks a tiny bit about alligators.  In figures they
show the field of view in one plane for Alligator,
Carcharadontosaurus, Tyrannosaurus, and House Cat.  The T and C
figures are obviously derived from Stevens' work; he also had access
to restorations of Daspletosaurus, Allosaurus, Nanotyrannus,
Velociraptor, and Troodon.  I presume all of these animals are in the
unrelated paper that Thomas R. Holtz, Jr. <tholtz@geol.umd.edu> just
coincidentally mentioned yesterday in the message where he described a
hypothetical paper that might be coming out soon and is actually
relevant to our discussion.  

In any case, back to Phil's point... I'm afraid I don't see it (any
and all puns intended).  The only issues that would cause Stevens
technique to fail would be issues that cannot be answered by looking
at living animals.  Those issues would be a) large protuberances that
left no records on the bones or associated traces in known specimens,
ii) weirdnesses in the dioptrics of the eye (the article specifically
suggests the quality of the cornea might be a problem, but I'd think
that the position of the lens and position/shape of the pupil would be
more important), and 3) the exact position of the eye in (or out of)
the socket.  The article specifically states that they didn't want to
make the animals too bug-eyed, but I don't know of any compelling
evidence that their eyes didn't protrude outside of their orbits.
None of these questions could be addressed by living animals unless...
You managed to find some sculptors who were very talented at sculpting
animals based on skulls and asked them to restore a bunch of animals
that they somehow managed never to have seen in whatever program of
study they took that gave them the skills to produce fleshed out
restorations, and after they completed their restorations you compared
the results of the Stevens method to measurements from living
animals...  Then maybe you could generate a lot of statistics on the
likelihood that any given animal's field of view might have been
overestimated due to an underestimation of the size of the stuff
blocking them, or to inaccuracies in the positions of the eyes and/or
their parts.  But still, Tyrannosaurs could have had eyes like
partially opened daisies -- each petal of the flower being analogous
to a feather that stuck out to protect the eye from the blood and guts
it took in with its typical meals.  Obviously I'm joking in that last
sentence fragment.  Their eyes were probably more like geraniums.

Mickey Rowe     (mrowe@lifesci.ucsb.edu)