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Re: New Jeholornis specimen



Greg Paul (GSP1954@aol.com) wrote:

<The shoulder glenoid of dromaeosaurs, troodonts, oviraptorosaurs shares
about the same degree of lateral orientation as Archaeopteryx, so it does
not provide evidence of relative grade of flight adaptation.>

  Based on?

  I am quite curious about this as it is not actually possible, given the
crappy means of preservation or flattening in anterior dorsals of most
known oviraptorosaurs and dromaeosaurids, not to mention that the only
complete shoulder for a troodontid is part of a juvenile skeleton or is
undescribed, this data appears to be presumptuous or based only on
external morphology of the scapulocoracoid girdle rather than the actual
nature and position it is in (just like you cannot actually tell what
orientation the shoulder of *Unenlagia* is in because the vertebrae and
ribs that allow you to articulate the scapulocoracoids are missing).

<As for the expanded finger base seen in all Jehol dromaeosaurs, no other
predator has evolved it. It is such a clear flight adaptation that all>

  ... other postulated pre-birds that would be secondarily flightless
don't have it. Or *Archaeopteryx*. So the thing must be either convergent
(if *Archaeopteryx* is basal to the dromaeosaurs as Paul [1988, 2001]
hypothesizes) or does not deal much in the actual nature of flight, but
just as a mechanical derivative as was actually considered by Tim Williams
whose relevance to flight was part of a suite, rather than by one or two
key features.

<other possibilities must be ranked as implausible unless really really
good evidence shows up indicating otherwise. Since basal dromaeosaurs had
much greater central finger flattening than Arch, and stiffening too, and
longer primaries relative to the hand, this is superb evidence of more,
advanced flight.>

  Except they didn't have the feathers, as in *Sinornithosaurus* TO fly
with, much less the sternal size, much less the other "flight-related
features" that *Archaeopteryx* shares with birds that are not present in
*Sinornithosaurus*.

<To argue otherwise is too dismiss powerful evidence on an arbitrary basis
and is not really scientific.>

  Let's not argue what is scientific, when the discussion in Paul, 2001,
as discussed earlier on this list, involves a great deal of _a priori_
assumptions of what the ürvogel really is, and what a flight related
character really is.

<There are so many advanced flight features in avepectoran dinosaurs that
far and away the best explanation is advanced relative to Arch flight,
it's way beyond mere parsimony.>

  I think Williams will agree here, given that this only argues about
flight performance and ability, not about avian origins, and the departure
of functional anatomy and phylogeny is one thing that needs to be
considered. Birds are not defined, nor should they be, by their ability to
fly, and the presence of feathers and so called "flight-related features"
in taxa that are not birds should attest to this. The possible multiple
origins of flight have not, I believe, ever been discussed in print.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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