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colour vision / skin pigmentation



Hello all!

If mammalian colour vision re-evolved after being lost during our
nocturnal lifestyle phase, does that mean reptiles/dinosaurs/birds might
have different retinal sensitivity modes than we mammals currently do?

Our colour vision is based on three photosensitive pigments, whose
sensitivities peak in the red, green and blue wavelengths, and our eyes
and brains reconstruct a subjective `colour' based on the differential
responses from the three types of cone cells.

Do living birds and reptiles also have a system of three retinal pigments,
and do those pigments have similar response profiles to ours?

It is known that many insects have the ability to discriminate among
colours in the near-ultraviolet: what look like plain white flowers to
us, really have high-contrast patches in UV and would look like brightly
coloured nectar targets to a bee or butterfly.  (Insects also sense
polarization characteristics of light, which might also be factored into
their sensation of `colour').  So the sensation of colour is not entirely
objective -- it depends on your sensing mechanisms.

It is possible that mammals did not entirely lose the ability to produce
the ancestral photopigment proteins, or even if they did completely lose
them, convergent evolution could still have re-created analogues of the
original set (since the three mammalian photopigments are variant forms
of a single protein, I believe).  However, if it is known that birds and/or
living reptiles have a different colour sense, this might have a bearing
on dinosaurian vision and coloration.

My point is, is it likely that dinosaurs' perception of their own colours,
and our perception of their colours, would be very close?  If not, what
differences might be possible?  For example, if they were hyper-sensitive
to variations among green colours which we cannot distinguish, to us
a stegosaur might look a generic, boring, drab green, but in their own
perception, have wild patches, patterns and stripes.  Conversely, if red
and green were indistinguishable by dinosaurs, they could have evolved
colours that would look bizarre to us, but were really the height of
camouflage in the eyes of their peers / predators.

----
Mike Bonham        bonham@jade.ab.ca      Jade Simulations International
``So, here I am, sitting by myself, talking to myself.  Now THAT's chaos!''