Tyrannosaur vision

[Mickey Rowe <mpqrowe@yahoo.com>]

John Hunt <john.bass@ntlworld.com> wrote:

> I am sure I will be corrected if I get this wrong.
> 
> The evidence for T rex having some binocular vision
comes from the
> cranial remains that seem to suggest that the back
of the skull was 
> relatively broad and the snout relatively narrow.

You're right; you will be corrected :-)

As Tom Holtz implied, the "evidence" is more like a
reconstruction of possible lines of sight.  To fill in
the gaps: Stevens had a restoration of the skull of a
Tyrannosaurus.  He placed a clear plexiglass screen in
front of it.  He took a laser and shined it through
the plexiglass toward the eye of the restored
tyrannosaur head.  He marked the location where the
laser light passed through the plexiglass to the eye. 
He repeated this from a variety of angles from which
the laser light just barely cleared the snout on its
way to the eye.  Connecting the marks on the
plexiglass and knowing how far away the plexiglass was
from the eye provided an estimate of the field of view
for that eye.

With its head angled slightly downward, it appears
that Tyrannosaurus had about fifty degrees of
binocular overlap.  By a similar metric, humans have
about a hundred and twenty degrees of binocular
overlap.

Anyhoo, Tom wrote:

] in a presentation by Kent Stevens at SVP several
years ago (that will
] hopefully see print someday soon).

The abstract appeared in 1997.  I'm sure you recall,
though, that the work was at least described in a
secondary source:

Coates, K.J. (1998). "Through Dinosaur Eyes", _Earth_,
7:2431.  

For more discussion of all of these issues, people
should also see:

Farlow, J.O. (1994). "Speculations about the
Carrion-Locating Ability of Tyrannosaurs. _Historical
Biology_, 7:159-165. 

> The evidence from CT scans of the braincase suggests
the optic 
> nerve was substantial

I think you meant, "The evidence from cranial
endocasts is that the optic tectum was relatively
large"

Aidan Karley <aidan_karley@yahoo.co.uk> asked:

} would the scleral plates constrain this? they're
anchors for eye-
} moving muscles, aren't they?

No, they are not.  In reptiles, the primary purpose of
the scleral ossicles appears to be to keep the front
of the eye from bulging out as muscles squeeze the
ocular lens to refocus it (i.e., to accommodate).

--
Mickey Rowe     (mrowe@lifesci.ucsb.edu)



                
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