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Re: Colored skin



>From: larrys@zk3.dec.com
 > 
 > There are a couple arguments for color either way - if we presume
 > birds are evolved from dinosaurs, the colorfulness of birds argues
 > for color in the past - and color provides camouflage.  However,
 > some arguments go back the other way: larger animals today are
 > seldom anything but gray - elephants and rhinos don't _need_ camo,
 > and they themselves don't have full-color vision, so it is useless
 > for signalling each other.

This is why one goes to other evidence for additional inut.
Many dinosaur groups have substantial display structures:
crests in hadrosaurs, spikes and knobs in pachycephalosaurs
and some ceratopsians, ridges and crests in most theropods,
the frills of ceratopsians and so on.

In living animals such display structures are almost always
brightly and vividly colored.  For instance in most living birds
with crests similar to those of some hadrosuars the crest is
bright red or yellow.

I rather like the reconstructions of ceratopsians with "eyespots"
on the frills.  Given the shape and orientation of the frills,
this seems a likely color pattern.

Also, the break-off point at which camoflage ceased to be useful
would have been at a larger body size then, since the carnivores
were *much* larger than they are now.  Thus many of the mid-sized
dinosaurs probably were camoflaged.

There is reason to suspect that adult sauropods were above the
size at which even the large theropods could normally deal with,
so I suspect that sauropods *were* mostly gray like elephants today.

 >  If, however,
 > they had color vision, as birds do, then color might have been heavily
 > involved in sexual displays - they might have had flashy, colorful
 > crests, bright displays on back or chest or face, and otherwise be
 > similar to our modern birds in terms of color use.  Sadly, we can't
 > yet prove this either way. 

Well, since color vision is widespread among tetrapods, and since
the structure of avian color vision is the same as that of reptiles,
it is almost certain that they have *retained* the primitive color
vision of tetrapods.   This effectively proves that theropods, at
least, had color vision.

[Mammalian color vision is based on a different system, and seems
to have re-evolved after being lost in the ancestral mammals,
probably due to the early mammals being nocturnal].

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.