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Re: black and white Archaeopteryx




--- Ronald Orenstein <ron.orenstein@rogers.com> schrieb am Mi, 12.6.2013:

> Von: Ronald Orenstein <ron.orenstein@rogers.com>
> Betreff: Re: black and white Archaeopteryx
> An: "rtravsky@uwyo.edu" <rtravsky@uwyo.edu>, "dinosaur@usc.edu" 
> <dinosaur@usc.edu>
> Datum: Mittwoch, 12. Juni, 2013 19:41 Uhr
> Melanin pigment may have a structural
> role rather than one relating to colour pattern.  It has
> been suggested that the dark tips on the wings of many
> otherwise white birds (e.g. many gulls) serve to strengthen
> the feather tips and resist wear.  Even if Archaeopteryx
> was not an active flyer a similar explanation might have
> been involved (e.g. protecting feather tips against abrasion
> through contact with vegetation, etc.). 

Even in passive flight, the flight feather tips experience high wear and are 
exposed to most significant forces.

Even "all-white" birds usually have black remex/rectrix tips. The only 
exceptions I remember spontaneously are High Arctic/Antarctic charadriiforms 
(Chionis and Pagophila - and in immature Pagophila, the flight feather tips are 
in fact black[*]).

While Neoaves have no bearing on character states in Archie, and while even 
powered flight obviously does not *mandate* melanin-strengthened feather tips, 
it is still very likely that in the absence of factors favoring hypomelanism 
(eg circannual snow/ice cover), remex tips in volant dinos will be blackish. It 
might not hold true for rectrices of "saururans", but this could perhaps be 
calculated.

One might even go as far as to say that BECAUSE Archie was for most purposes 
restricted to passive flight, hypermelanic remex tips were necessary: if one 
flies as badly as Archie, even the (absolutely) smallest improvement confers a 
(relatively) large increase in fitness.

That all nonwithstanding, the hypo-hypermelanism spectrum is one of the most 
trivial cases of variation. There are few terrestrial metazoans in which there 
isn't such variation present in the gene pool almost at a constant basis: it 
rarely gets fixed, but if very fa
tion face patterns in crown Aves).

So it is reasonable to assume that at least the remix tips of all volant 
theropods were hypermelanic. Finding them is not a surprise; it suggests, 
however, the methodology is reliable & can be used to determine contour plumage 
patterns too.


Regards,

Eike



[*] Obviously social/age-recognition pattern to decrease adult-offspring 
competition. It is remarkable because it is extremely minimalistic: 
http://birding.typepad.com/.a/6a00e5505da11788340120a6e5637e970b-800wi the 
camouflage is compromised as little as possible. Where does the black occur? On 
the belly? On the crown? On the rump? No. Only where it is most advantageous.