Re: Fate of Protoarchaeopteryx(Pygostyle origins?)

["Jaime A. Headden" <qilongia@yahoo.com>]

Bog moy! I wrote:

<Related ness of type of pygostyles depends on use; we can posit
that the tails of ankylosaurs and *Nomingia* are not comparable,
but can we posit the same for *Nomingia* and birds?>

Ekaterina Amalitzkaya (eamalitz@hotmail.com) wrote:

<What is the evidence that the classical avian pygostyle evolved
as a locomotor adaptation[?].>

  Pygostyles appear subsequent to the reducion of the _M.
caudofemoralis longus_ from the caudal vertebrae, in theropods
-- any taxon in this group with a pygostyle or comparable
stiffened tail (birds, dromaeosaurs, oviraptorosaurs, etc.) have
reduced caudofemoral musculature, as posited by Gatesy in
various publications. I'd need to dig into them, but maybe Steve
can provide a few relevant ones. I have read nearly all of them,
though, I'd just need to _find_ them all :). This only suggests
that pygostyles in theropods are related in some way to
locomotion, or after the tail was freed from the legs, which is
nearly the same thing in context to "bird" evolution. The tail
fan in *Archaeopteryx* is preserved on a stiffened tail that
lacks pygostyle fusion, but this does not mean it is not
analogous to the pygostyle, but that the tail acts as a
pygostyle for its length, as in dromaeosaurs. Oviraptorosaurs
have more flexible tails, but with distinct shortening and
specialization towards the distal end, and in *Nomingia* this
appears to be advanced to the point of fusion. Why? I suggest
that stress in aerodynamic utility is the point of pygal fusion
in *Nomingia*, and that later birds relocated the lateral
retrices away from direct contact to the pygostyle in relation
to the increase size of the retrices but shortening of the tail
as a whole. Why the tail shortened so much is another question.

<Currently this hypothsis has not been tested.>

  Not it hasn't. I am currently looking into it. The first step
has been taken (Gatesy) to relate caudal function. The next is
the development and actual function of the pygostyle (this has
also been done, in relating use and relationship of the
pygostyle to retrices). The third is the evolution of the
pygostyle, and this looks like its related to both feathers
(stress) and the locomotor module, which is the operating
thoery. Greg Paul and Scott Hartman have both offered display
and/or aerodynamic function as the leading development for the
arrangement of the feathers, Scott on the assumption that the
arrangement of feathers is to the distal ends of the limbs,
whereas Tom Hopp and Mark Orsen have put forward the theory that
they are brooding "umbrellas" which is equally advantageous, and
can work in both previous theories. This is not my point,
however, but the relationship of the fusion of vertebrae to cope
with increased stress. This suggests to me caudal fusion is
irrelevant to remigial development, but intrinsic to retricial
development as we see in *Archaeopteryx* (etc.)

<It is clear that though Archaeopteryx lacked a pygostyle it
could fly.>

  I didn't say the pygostyle is related to flight, but to
locomotion in an aerodynamic way. They are not exactly the same.

<Given that all current phylogenetic analysis strongly suggests
that origin of flight was merely an oppportunistic sideshow of
the insulation problem.>

  How so? We see in dromaeosaurs terrestriality with flight
related features. There's not a single Liaoning theropod over
7ft. in length. There are comparable theories that integument in
smaller animals is _required_ towards an ectothermic paradigm
because of increased heat loss with decreased surface area and
less distince between surface and body core. Insulation is
required, but whether this preceeded flight or was _lost_ in
dromaeosaurs proper and so forth has not been tested.
 
<Further two fairly distinct early forms like Protopteryx and
Confuciusornis show long tail feathers.>

  Very unsual, _solid_ long tail feathers, without
differentiated vanes, but frond-like formation. Secondary to
differentiated vanes, if we want to make a point of the current
placement of *Archaeopteryx* and *Caudipteryx* ....

<Thus an equally likely scenarios is that pygostyles had nothing
to do with flight to start with but with intraspecific display.>

  How so? Can you separate the stress-driven fusion of vertebrae
from the development of a series of fused caudals? Or better
yet, how do you explain the fusion of a pygostyle when a bird
like *Archaeopteryx* (whom we posit as a flier) can have a tail
fan [for flight] but no pygostyle? Or the abscence of one in a
non-flier with distinct tail fan [see *Protarchaeopteryx* and
*Caudipteryx*]?

<Looking a something as big as Unenlagia with all its bird like
features of its pectoral region does it even make sense that
flight was the principle selective force?>

  It seems to me that *Unenlagia* is an example of gigantism
when it's closest morphological relatives appear to be
*Bambiraptor,* *Rahonavis,* and *Sinornithosaurus*....

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

__________________________________________________
Do You Yahoo!?
Yahoo! Auctions - buy the things you want at great prices
http://auctions.yahoo.com/