Re: Feathered Dragons: Studies on the Transition from Dinosaurs to Birds

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

Scott Hartman (DinoBoyGraphics@aol.com) wrote:

<I have to comment on this:  There is no reason to think that the
rectrices on the hind limbs of Microraptor could not fold back against the
leg during terretrial locomotion:  If not, they would have been destroyed
during anything bu the most limited of arboeal locomotion as well.  Also,
Nick did not conlcude that the feathers on the hind limbs of Archaeoptery
were anywhere near as long as in Microraptor, although he speculated that
their presence might indicate that leg "wings" were primitive for the
group.>

  I would also like to say that unless there was a special novel muscular
anatomy of the legs not seen in any bird, croc, lizard, or other tetrapod
known today that would have been able to control such feather-moving
structures, this is one of the more unparsimonious arguments to assume
that these animals were particularly terrestrial _and_ capable of
maintaining leg-feather security.

<Unless and until someone can show that the the pelvis and/or femora of
sinornithosaurs were in some way diferent from other theropods (including
Archaeopteryx), then they would make poor arboreal scansors. I don't mean
that they couldn't climb, but they were not doing the squirrell or lemur
thing in trees.>

  Greg Paul only proposed (without direct evidence) that the femora could
laterally/dorsally extend to explain leg _flapping_, rather than
sprawl-legged climbing. Avian femoral orientation laterally from the belly
has been explained not as a climbing adaptation, or even particularly
arboreal, but as an accomodation of the visera beneath the pelvis and the
requisite widening of the thorax and pelvis ... the femora had to orient
laterally to accomodate. And they need not have been capable of being
squirrels or lemurs to still be at least halfway arboreal or scansorial,
or spending enough time in the trees to adapt their legs into "butt-fans,"
without any possible benefit on the ground (as to explain a terrestrial
locomotor module, they must apparently be "tucked away"); the feathers
also show the same increasing distal symmetry of their brachial remiges,
implying a direct aerodynamic connection, and likely for some form of
flight advantage, whether they were flapping or not.

  Tucking the legs up underneath the body preserves the inferred narrow
pelvis of basal deinonychosaurs (as in *Sinovenator* and *Microraptor*),
the short femoral neck of basal deinonychosaurs, and the arrangement of
the  leg feathers in *Microraptor* for aerodynamic purposes. To get to
such a posture, most likely, a leap from a tree would be best. To lead to
such an exaptation, many, many leaps would be required in its evolutionary
history, implying there had to be a significant amount of time spent in
high places, be they cliff or tree.

  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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