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Re: 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?

One clarification - since the basal tetrapod condition is nocturnality (or
at least most active in dusk - the state in amphibian and most of the
primitive mammals, as well as some of the fish outgroups), mammals may not
have "lost" good color vision.  They may have never had it in the first
place.

>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?

Yes.  I know there are several researchers (whose names have all slipped my
mind right now) who have shown that sauropsids (birds & reptiles) have four
or five different photosensitive pigments.

[two paragraphs deleted.]

>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.

You may have hit the nail on the head here.  I believe part of the projects
currently underway (or at least planned), are to see how the color
variations on birds (and hopefully some lizards, while they're at it)
appear under different optic regimes.

[Note that this idea is used to a certain degree in the book [or was it
Marxist propaganda ;-)] Dinotopia.  Gurney compares a seen as scene by
human eyes, and the same by dinosaur eyes.  Of course, it should be
impossible for a human to see what the four- or five-based pigment color
scheme looks like, in the same way that printing an image scanned a 1200
dpi will only look like 300 dpi if printed on a 300 dpi printer...].

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.