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Re: New Jeholornis specimen
Gregory S. Paul 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.
Or, I would say, it therefore does not provide direct evidence of flight at
all. In the context of the rest of _Archaeopteryx_'s anatomy, it's sensible
to regard the lateral glenoid as assisting in powered flight (i.e. execution
of flight stroke). Yet, even in this context the lateral glenoid (as
opposed to dorsolateral glenoid, as in more derived birds) precludes
elevation of the wing above the horizontal.
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 possibilities must be ranked as implausible unless really really good
evidence shows up indicating otherwise.
As I've heard historians lament: the future contaminates the past. Features
that incontrovertibly assist powered flight in modern birds may not
necessarily have performed this same function in non-flighted ancestors.
This is certainly true for the furcula; why not other pectoral and forelimb
What I find troubling is that, under your hypothesis, so many flight-related
features in birds are held to have evolved specifically *for* flight. This
leaves me to wonder what anatomical features pre-flight theropods had for
evolution to work on. What preadapted these critters to powered flight?
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. To argue otherwise is too
dismiss powerful evidence on an arbitrary basis and is not really
I have yet to hear an argument why such adaptations could not have been
employed for aerial gliding, rather than powered flight. For example, no
gliding dromie wanted the primaries to detach during the aerial phase
(especially if the long primaries "snagged" on branches during the glide) or
during prey handling on the ground. One hypothesis is that basal dromies
used the hands to wrestle with prey more so than _Archaeopteryx_. This
favored a firmer and broader base for attachment of the primaries.
As for the proportionately longer primaries, this was to reduce wing loading
in basal dromies - after all (with the exception of _Microraptor_) these
were bigger and heavier animals than _Archaeopteryx_.
These competing hypotheses, I think, are scientific.
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