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Re: Feathering in coelurosaurs



At 10:51 2000-04-05 PDT, Matthew Bonnan wrote:

It is true that essentially all large birds have rather dull plumage.
However it is worth noting that many of the larger birds have brightly
coloured patches of skin or wattles usually in the head region (e. g.
Cassowaries, Cranes, Crowned Cranes, Ground Hornbills, New World Vultures,
some raptors etc.). These usually have some kind of signalling function to
conspecifics.  The same might well have been true of non-avian dinosaurs.

Large "reptiles" also tend to be dull (though some boids have rather
striking patterns), small squamata on the other hand can be extremely
bright-coloured and the same is true of small snakes and small turtles.
There does seem to be a definite correlation large size = dull color here,
perhaps simply because large animals do not need bright colours to
advertise their presence or to warn off predators (I'm poisonous/dangerous). 

Tommy Tyrberg



>Just to throw my hat in the ring here:
>
>Does anyone know of a large reptile that is brightly colored or even 
>colorful?  As far as I know, crocs, large snakes (Anacondas, boids, etc.), 
>Galapagos turtles, and the like are all relatively dull colored animals, 
>even though all of these reptiles see in color (please correct me if I'm 
>wrong).  On the avian side of things, ostriches, emus, and other large 
>ground birds are relatively drab as well.  I don't pretend to know why this 
>is, but it's interesting.  What is it about getting larger in both these 
>groups that seems to dull their colors?
>
>If we use a phylogenetic bracket hypothesis, then, we might be able to say 
>this, if birds and crocodilians represent the living outgroups to dinosaurs: 
>(A) Since both crocs and birds have color vision, that would make it a 
>"primitive" or symplesiomorphic trait for dinosaurs and all ornithodirans; 
>(B) Based on this hypothesis, dinosaurs would have primitively had color 
>vision; (C) This might imply colorful patterns for display or deception, but 
>of course none of this testable.  Dinosaurs may have been drab animals when 
>they became larger, if the trend we observe in living avians and 
>crocodilians holds true for all archosaurs.  Are there any large archosaurs 
>that are very colorful?
>
>I suppose in the end, if the current relationships between dinosaurs and 
>birds and crocs hold, we can be reasonably sure that dinosaurs were 
>primitively color-seeing animals.  What colors they were, or if the large 
>dinos were color-impaired, is at the moment beyond the reach of a direct 
>scientific inquiry.  While we're all waiting for cloning to bring back 
>dinosaurs (and Matt Wedel will agree with me that sauropods should be the 
>first to be cloned), maybe an area of investigation would be to study skin 
>coloration in large and small archosaurs and see if there is some 
>integumentary reason for the "color change" with size.
>
>Matt Bonnan
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