Re: Dinosaurs and birds

[Dann Pigdon <dannj@alphalink.com.au>]

David Marjanovic writes: 

> So the problem shifts: how do 
> you get a wing -- or half a wing -- as the result of selection for 
> something unrelated to locomotion? I can think of at least two proposals. 
>
> One is the idea that wings are for brooding (Hopp & Orsen 1998 -- 2004)... 

> The other is that wings evolved as display surfaces and similarly became 
> used in courtship fights that culminated in flight (Cowen & Lipps in Cowen 
> 1994): http://www.dinosauria.com/jdp/archie/feather.htm ...

The problem with both scenarios is that we have fossils of animals like 
*Saurornithosaurus* that are clearly juveniles, yet have fully-developed 
'wing' fans. Neither brooding nor display structures would be expected to 
form until an animal reaches adulthood. Certainly amongst extant animals, 
such biologically expensive features as lions' manes or gargantuan peacocks' 
tails don't develop until they're old enough to need them. They'd be 
down-right maladaptive on juveniles. 

Of course, Early Cretaceous dromaeosaurids may have been nothing like 
pre-flight avetheropods (of which we have zilch fossils). 

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Dann Pigdon
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://heretichides.soffiles.com
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