Re: Science feather strength debate

[Tim Williams <tijawi@gmail.com>]

Augusto Haro <augustoharo@gmail.com> wrote:

> May the lenght of the forelimb coupled with the inferred phylogenetic
> allegiances of the material (with recent birds), still suggest so?


Length of forelimb:

Many coelurosaurs have elongated forelimbs, although those of
_Archaeopteryx_ are among the longest (outside Ornithothoraces).
However, there is no reason to automatically assume that forelimb
elongation in a feathered non-ornithithoracine theropod is
flight-related.  Longer forelimbs also improve reach - such as for
prey capture (e.g., dromaeosaurs), or procuring branches (e.g.,
therizinosaurs), or possibly climbing (e.g., _Yixiansaurus_,
_Epidendrosaurus_).


Having said that, the type and arrangement of feathers in
_Archaeopteryx_ does certainly indicate some form of aerial behavior.
But this returns me to my original point: it's the feathers that are
telling us this, not the skeleton.  Osteologically, there is nothing
about _Archaeopteryx_ that points to it being a flier.  We tend to
interpret the osteology of _Archaeopteryx_ through the prism of its
feathered plumage.  IMHO, it should be the other way round.


Inferred phylogenetic allegiances:

This depends entirely upon the phylogenetic position of
_Archaeopteryx_ vis-a-vis modern birds (crown Aves).  If
deinonychosaurs and/or oviraptorosaurs are found to be closer to crown
Aves than is _Archaeopteryx_, then the hypothesis that _Archaeopteryx_
was a powered flier is undermined even further.


Current phylogenies, in which _Archaeopteryx_ forms a clade with crown
Aves to the exclusion of deinonychosaurs and oviraptorosaurs, don't
actually point to _Archaeopteryx_ being a powered flier.  This is
because wings composed of closed pennaceous feathers occur outside
this clade, having been found in some deinonychosaurs.



Cheers

Tim