Re: Fwd: Re: How would Tyrannosaurus approach a Triceratops?

[Jura <pristichampsus@yahoo.com>]

--- Aidan Karley <aidan_karley@yahoo.co.uk> wrote:

> (forgot to send this to the list, instead of just to
> Neal)
> 
> --- Neal Romanek <nromanek@earthlink.net> wrote:
> 
> > T-Rexes did have binocular vision however, yes?
> > 
>     I'm not sure, and being back at sea with a slow
> internet
> connection, I hesitate to try to find out. I recall
> having heard it
> mentioned, but I'm by no means certain. Thinking
> about it, wouldn't
> the snout have got in the way of most directions of
> binocular vision?
> With the head down and charging at Lunchospikysaurus
> (gen. nov. but
> short-lived <G>) then the zone of vision above the
> snout line would
> have included the target and been potentially in
> stereo. I'm not so
> sure when T-rex is staring down his nose at L.
> though.

+++++++++++++++++++++++++++++++

See HP Jaime Headden's post on the osteological
correlates to binocular vision in _T.rex_. 

As for looking down his snout, I'm more fond of the
alternative way for large theropods to view their
prey. Instead of looking straight down the snout, they
could look up from it. This removes most of the
cumbersome snout from the field of vision, and should
greatly increase depth of field. 

It's not all that weird either. Humans and other
primates look up from our snouts all the time.
Crocodylians can do it too (helpful for seeing prey
from the water's edge, without drawing attention to
oneself).

The snout angling wouldn't have to be all that extreme
either. Just a slight (45 degrees or so) dip to get a
better view of things. 

 
> > On Aug 18, 2005, at 3:45 AM, Aidan Karley wrote:
> > 
> > > Elevation of the head is OK, but the evidence
> for "superior
> > > eyesight" in T-rexes (over ceratopsians) is?
> > 
> > 
>    I was thinking in terms of visual acuity,
> possibly colour
> sensitivity too, rather than binocular capability.
> Is the improved
> depth perception that may go with a stereoscopic
> overlap "superior"
> to the 300deg + field of vision given by having your
> eyes mounted on
> either side of the head? I'd agree they're
> different, but I'm not
> sure they're sufficiently comparable to say one is
> "better" than the
> other. 

++++++++++++++++++++++++++++++++

Without assigning a context to the term "superior,"
there is no point in using it. Stereoscopic vision is
"superior" to 360 degree (but essentially 2
dimensional) vision for judging depth. 360 degree
vision, on the other hand, is "superior" to
stereoscopic vision when it comes to field of view. 

So a predator that relies on chasing down prey, would
benefit from having stereoscopic vision, more so than
the 360 vision. Herbivores, on the other hand, don't
need to accurately judge the distance between them and
their plant of choice. Rather, they benefit more from
being able to see the widest field of view possible,
so they don't get snuck up upon. 

As for the often underrepresented myriad of other
creatures that play both predator and prey, there
seems to be a toss up on the better vision types. If
one is small and tasty, then it probably behooves one
to keep one's eyes to the sides, and deal with a
harder to judge depth of field when chasing insects. 

If one is larger, and can put up a decent fight, then
it might make more sense to have stereo vision to
better hunt down the larger prey one needs to survive.

And if one is a chameleon, then you get to laugh at
all the other guys, because you get to have both types
of vision.

> Some birds at least have colour vision - need it
> to recognise the
> mate's plumage - which returns to the previous
> question of if this
> would leave identifiable evidence on brain casts?

+++++++++++++++++++++++++++++++++++++++++++

Monochromatic vision is mostly unique to mammals. Most
other animals (and especially reptiles) are capable of
seeing in more colours than we can (including UV). 

Since dinosaurs are squarely placed between birds and
crocodylians, and since both of these outgroups
possess colour vision, the general consensus is that
dinosaurs had colour vision too. 

As far as I know, there is no morphological evidence
to suggest one way or the other. There is just the
phylogenetic evidence (which I'd say is pretty strong
for this case). 

The only dinos that would see in black and white,
would have to be ones that secondarily lost it.
Possibly as a result of nocturnality (this is no
guarantee though, as nocturnal geckos can still see
colour).

Jason

"I am impressed by the fact that we know less about many modern [reptile] types 
than we do of many fossil groups." - Alfred S. Romer


                
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