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Re: Science feather strength debate



2010/11/3 Tim Williams <tijawi@gmail.com>:

> 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_).

All possibilities, but one can say, using the EPB, that these
considerations imply behaviours (and thus parts of soft anatomy) that
are not primitive for the two extant clades bracketing Archaeopteryx,
while flight is for one of these clades (and thus would lead, at least
for this behavior, to a more parsimonious character evolution
hypothesis). Of course EPB is not all there is in life, and you also
have mechanics, but then one can doubt, as one doubts of the flight
capabilities of Archaeopteryx, how good are the long stiff fingers of
Archaeopteryx in grasping prey, and, as you previously indicated in a
former discussion with me, that the general anatomy of Archaeopteryx
does not suggest it to be quite a climber (branch procuring for such a
small animal should be related to climbing and to the deficient
grasping capabiities of the hand).

> 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.

May be, although there is the development of the deltoid insertion
area Ruben (1991) indicated. Anyway, I think both are useful evidence
(perhaps intrinsically capable of generating different arguments) and
I do not see reasons by which to prefer one to the other except for
the possibly greater amount of mechanical data provided by the
skeleton and the inferred musculature. Of course, display and a
variety of non-adaptationist morphogenetic hypotheses can be also
raised. I just said the ostelogical features of Archaeopteryx may have
suggested (in a paralell world with an Archaeopteryx without feathers)
scientists it was a flier, not that it was the only one hypothesis it
could conceivably arise to these scientists.

> 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.

Yes, but as far as I know (and think you agree), these hypotheses are
not favoured nowadays by most studies and thus cannot be used to
dismiss the possibility of Archaeopteryx being a power flier.

> 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.

True, current phylogenies do not require Archaeopteryx to fly, but in
my viewpoint it is so because as one of the clades bracketing the EPB
does not fly and the other does, assuming each condition for
Archaeopteryx is equally parsimonious. And you are right in that
feathers do not make a flyer, as can be also seen in many Recent
birds.