Re: Evolution of flight

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

Allan Edels wrote:
> 
> Dann (et al):
> 
>     My understanding of _Archaeopteryx_ being called the first bird is that
> it shares many other bird characters besides feathers, such as reduced
> number of teeth, arm structure, and the "wishbone".  (Also, the specific
> feathers found indicate that _Archaeopteryx_ could fly).
> 
>     Allan Edels
>

Yet isn't a reduce number of teeth one of the characteristics of
'advanced' theropods? The arm structure (more specifically the
scapula) of Unenlagia is said to be quite bird-like, and furculas
have been identified in other theropods (Oviraptor I believe).
Oviraptor had a greatly reduced number of teeth and a furcula. If
it also had a covering of feathers, would this make it a bird?
        Archaeopteryx was mistaken for a small compsognathus-like
theropod for a long time before anyone noticed the feather impressions.
I would assume that Aves was originally defined on the basis of
living animals only. If this is so then 'true' birds, by the strictest
definition, would include only those animals going back to the
most recent common anscestor of extant varieties. I'm not saying
that early flying theropods weren't bird-like or somehow related,
but calling them birds may be stretching the definition of Aves
somewhat (assuming the above definition is correct of course).
I think it says more about trying to define living (and extinct)
systems by ways of discretely defined units than anything else.
The real world is a continuum, and any descriptive units us mere
humans try to impose on the natural world will always have problems
in the 'grey' areas.
-- 
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        Dann Pigdon
        Melbourne, Australia

        Dinosaur Reconstructions:
        http://www.geocities.com/capecanaveral/4459/
        Australian Dinosaurs:
        http://www.alphalink.com.au/~dannj
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