Re: Doin the Theropod Nod

[Mickey Rowe <rowe@psych.ucsb.edu>]

dbensen@gotnet.net asked:

> So, if dinosaurs didn't need to bob their heads, would they need to
> cock their heads like birds do when they want to look closely at
> something?

Probably not.  Once again (as you've inferred), the lack of
extra-ocular muscles is the primary reason that birds have to cock
their heads in order to get better views of objects.  To expand a
bit...  Animals vary in the extent to which their retinas vary across
space.  We have a very high density of cone photoreceptors at one
point in each eye, and our cone density falls off pretty quickly as
you move away from that point.  Some animals have no such regions of
higher density, and hence no real reason to prefer to use one part of
their eyes over another.  Birds typically have two regions of high
cone density, each associated with different behaviors.  Thus they may
alternately direct one of these "foveas" at an object and then the
other.  Lacking an ability to rotate their eyes they must rotate their
heads in order to accomplish this task.  Also, at least some birds
have a gradient in cone density such that they have higher acuity on
the top of their retinas (the part that's "looking" down) than the
bottom.  Thus to get a good luck at a higher object they may turn
their head almost upside down.  But again, if they could rotate their
eyes without rotating their heads, they would most probably do so.
And other dinosaurs -- to the extent that their retinas were
inhomogeneous -- more probably could and did rotate their eyes rather
than their heads as much as possible.

Keep in mind that there's a good deal of speculation here, but this is
the world as I see it (did everyone just roll their eyes?)

-- 
Mickey Rowe     (rowe@psych.ucsb.edu)