Re: Sclerotic rings

["David Marjanovic" <david.marjanovic@gmx.at>]

Aaah!! Easter holidays! TIME!!!

> Gordon Martin Human wrote:
>
> > Given that eyes are filled with fluid, and fluids are by nature
> > incompressible, I don't see this as a valid hypotheses.
>
> Fluids are incompressible, but fluid-filled sacks can be deformed, so it
> isn't a priori crazy that a compensatory structure might be of use
> in maintaining visual acuity (whether the pressure comes from depth,
motion
> or whatever). As for whales, are any of them primarily visual hunters?
Animals
> which use echo-location should have less stringent visual requirements, so
> maybe they aren't really comparable anyway?

Ask any professor of physics -- fluids ARE compressible, just less so than
gases and spongy solids.

Sclerotic rings are a synapomorphy of vertebrates or a similarly inclusive
clade, so their absence in some forms (mammals AFAIK) must be explained, not
their presence (in all well-enough-known dinosaurs, for example). Giant
squid have no sclerotic rings and neither AFAIK anything similar. Does
anyone have an idea what sclerotic rings are good for? Just protection?

No whales rely much on their eyes, those that hunt use echolocation (unlike
ichthyosaurs, some of which had the most humongous eyes ever), and those
that eat plankton basically open their mouths. :-)