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Re: Avian Ancestors, new book on theropods



-------- Original-Nachricht --------
> Datum: Fri, 1 Mar 2013 18:35:42 +1100
> Von: Tim Williams <tijawi@gmail.com>

> (3) The feather is just one part of the flight apparatus of birds.
> The osteology and the musculature have to be biomechanically competent
> to execute a thrust-generating flight stroke.  On this issue, there is
> some doubt over whether _Archaeopteryx_ could flap its wings.  One
> interpretation is that the shoulder joint orientation precluded
> elevation of the humerus higher than the back - so no recovery stroke,
> no powered flight.  Added to this was the extremely weak pectoral
> musculature (compared to modern birds).

Are you sure about that last point? As preserved (and that only in the Berlin 
specimen), the sternum was very small; but can we tell if the whole thing 
calcified?

And on the other side of the pectoral muscle, the deltopectoral crest is huge. 
This also allows large deltoid muscles for raising the wings -- bats use their 
deltoids for the upstroke.

> AFAIK, there is no widely-held belief that the asymmetrical feather
> evolved only once.

It's at present the most parsimonious option, though, isn't it?