Re: On the Issue of Sprawling Dromaeosaurs (long)

[Dino Guy Ralph <ralph.miller@alumni.usc.edu>]

I don't know who to credit for the idea, but it has been pointed out that it
makes sense for a feathered gliding or flying animal to have asymmetrical
flight feathers, as this would prevent the feather vanes from twisting about
the rachides during forward motion, and thus this characteristic would serve
to preserve the integrity of the flight surface and maintain a smooth,
streamlined contour.

Except in the case of tail feathers which are modified for display, the
asymmetrical aspect of flight feathers is as pervasive in the rectrices as
in the remiges of extant flying birds, so flapping per se is not what
determines the location of asymmetrical feathers in modern birds, but rather
the position and function of the appendages with respect to the airstream.
And this is one reason why I would expect the lengthy hindlimb wing feathers
of little basal dromaeosaurs to serve some function in aerial activity, even
if we don't understand precisely how the hindlimbs would come into play.

The fact that a marsh wren can have much greater flexibility in its
hindlimbs than its close relatives suggests to me that some basal
dromaeosaur species may have likewise incorporated a small series of
hindlimb modifications to optimize climbing and flying.  The assertion that
their anatomy wouldn't have permitted them this additional flexibility via
the same adaptations as the marsh wren shouldn't preclude them from having
achieved the same end by a different set of character transformations.
Convergence happens.

Given that later dromaeosaurs possessed all the pectoral and forelimb
prerequisites essential to wing flapping, and that -- in addition to this -- 
_Microraptor_ / _Cryptovolans_ were equipped with large, ossified sterna, as
well as more bird-like manus than _Archaeopteryx_, it seems to me reasonable
to hypothesize that these "four winged dinosaurs" could  have used their
forelimbs to assist their progress through the air.  Are there any
osteological features which would falsify the hypothesis that these small,
early dromaeosaurs could have moved their arms during aerial locomotion?
--------
"Dino Guy" Ralph W. Miller III
Docent at the California Academy of Sciences
proud member of the Society of Vertebrate Paleontology